JP7679074B2 - Semiconductor light emitting device, method for fabricating semiconductor light emitting device, and contact structure - Google Patents

Description

The present invention relates to a semiconductor light-emitting device, a method for fabricating a semiconductor light-emitting device, and a contact structure.

Patent Document 1 discloses an optical semiconductor element. This optical semiconductor element includes a compositionally graded layer exposed by etching and an n-side electrode that is in direct contact with the compositionally graded layer.

Patent Document 2 discloses a nitride semiconductor light-emitting device that includes an n-contact layer, an Al _y Ga _1-y N material layer (0≦y≦0.5, fixed Al composition) provided on the n-contact layer, and an n-side electrode that is in direct contact with the Al _y Ga _1-y N material layer.

Patent Document 3 discloses a nitride semiconductor ultraviolet light emitting device. This nitride semiconductor ultraviolet light emitting device has an n-type contact layer that has a smaller AlN mole fraction than the n-type cladding layer and is provided between the n-type cladding layer and the n-electrode.

Patent document 4 discloses a p-type cladding layer with an Al composition that gradually decreases from the electron blocking layer to the p-type contact layer.

Patent Document 5 discloses a nitride semiconductor light-emitting device. This nitride semiconductor light-emitting device includes a compositionally graded layer having an Al composition y that decreases from the surface in contact with the carrier barrier layer toward the surface in contact with the second group III nitride semiconductor layer.

JP 2019-110168 A JP 2010-161311 A JP 2012-089754 A JP 2016-171127 A JP 2019-110195 A

In the blue and longer wavelength regions, semiconductor light-emitting devices using group III nitrides have an active layer including a GaN (gallium nitride) barrier layer and an InGaN well layer, and are fabricated on a GaN template layer on a sapphire substrate or a GaN substrate. In contrast, in the ultraviolet wavelength region, semiconductor light-emitting devices have an active layer including, for example, an AlGaN barrier layer and an AlGaN well layer, and are fabricated on an AlN (aluminum nitride) template layer on a sapphire substrate or an AlN substrate.

For example, when considering a blue semiconductor laser from an electrical perspective, the n-type semiconductor is provided with low resistance due to the silicon-doped GaN. On the other hand, the p-type semiconductor is provided with higher electrical resistance than the n-type semiconductor due to the use of magnesium dopants and AlGaN.

When considering a semiconductor light-emitting device that provides ultraviolet, e.g., deep ultraviolet, wavelength region light emission from an electrical perspective, magnesium is added to AlGaN with a large Al composition compared to the AlGaN of blue semiconductor lasers for the p-type semiconductor. Although silicon can still be used as a dopant for the n-type semiconductor, the base semiconductor is changed from GaN to AlGaN or AlN with a high Al composition due to the use of an AlN template layer or an AlN substrate.

Comparing blue light-emitting devices and ultraviolet light-emitting devices from the perspective of n-type semiconductors, in blue light-emitting devices, particularly semiconductor lasers, the Al composition is increased from the GaN semiconductor substrate toward the active layer to achieve carrier confinement. On the other hand, in ultraviolet light-emitting devices, such as deep ultraviolet light-emitting diodes, the Al composition is decreased from the AlN semiconductor substrate toward the active layer to achieve an Al composition that enables the emission wavelength of the active layer.

Thus, deep-ultraviolet semiconductor light-emitting devices are being developed in a different material environment than longer-wavelength blue light-emitting devices.

Patent Document 1 discloses the formation of an n-side metal electrode that makes direct contact with the compositionally graded layer. In the optical semiconductor element of Patent Document 1, the compositionally graded layer surface with which the n-side electrode makes contact is formed by etching. Manufacturing variations in the amount of etching cause the Al composition of the compositionally graded layer surface with which the n-side metal electrode makes contact to vary within the plane and from lot to lot.

Patent Document 2 discloses forming an n-side electrode in direct contact with an AlGaN material layer of fixed Al composition provided on an n-contact layer. Patent Document 3 discloses forming an n-side electrode in direct contact with an n-contact layer provided on an n-cladding layer and having a smaller AlN mole fraction than the n-cladding layer. Patent Document 4 teaches gradually decreasing the Al composition of the p-cladding layer to improve device life. None of Patent Documents 2 to 4 teach an n-side composition-graded layer.

In view of the above-mentioned problems, the present invention aims to provide a semiconductor light-emitting device having an n-side contact structure that can provide good electrical characteristics over a wide range of Al compositions, a method for fabricating a semiconductor light-emitting device, and a contact structure.

A first aspect of the present invention is a semiconductor light-emitting device comprising: an n-type semiconductor layer comprising a group III nitride semiconductor containing aluminum as a group III constituent element; a p-type semiconductor layer provided on the n-type semiconductor layer; an active layer comprising a group III nitride semiconductor and capable of generating deep ultraviolet light provided on the n-type semiconductor layer; an n-type contact layer of a group III nitride semiconductor containing gallium as a group III constituent element provided on the n-type semiconductor layer; an n-type intermediate region of a group III nitride semiconductor containing gallium and aluminum as group III constituent elements provided on the n-type semiconductor layer; and an n-electrode containing a metal, the n-type intermediate region being provided between the n-type contact layer and the n-type semiconductor layer. The n-type contact layer is provided between the n-type intermediate region and the n-electrode, the n-type intermediate region has an Al composition X that changes monotonically in the direction from the n-type semiconductor layer to the n-type contact layer (including changing in the same direction in a step-like manner), the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the Group III nitride semiconductor of the n-type contact layer, the Al composition Y of the n-type contact layer is equal to or greater than zero, the Al composition X of the n-type intermediate region is equal to or smaller than the Al composition Z of the n-type semiconductor layer, and the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are sequentially arranged in the direction of the axis from the n-type intermediate region to the n-electrode.

A second aspect of the present invention is a method for producing a semiconductor light-emitting device, the semiconductor light-emitting device including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, the active layer including a Group III nitride semiconductor capable of generating deep ultraviolet light, the method including: growing a first Group III nitride semiconductor layer for an n-type intermediate region containing gallium and aluminum as Group III constituent elements on a substrate; growing a second Group III nitride semiconductor layer for an n-type contact layer containing gallium as a Group III constituent element on the substrate after growing the first Group III nitride semiconductor layer; and forming an n-electrode including a metal on the substrate after growing the second Group III nitride semiconductor layer, the n-type semiconductor layer including aluminum as a Group III constituent element. The n-type intermediate region is provided between the n-type contact layer and the n-type semiconductor layer, the n-type contact layer is provided between the n-type intermediate region and the n-electrode, the n-type intermediate region has an Al composition X that changes monotonically in the direction from the n-type semiconductor layer to the n-type contact layer, the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the Group III nitride semiconductor of the n-type contact layer, the Al composition Y of the n-type contact layer is equal to or greater than zero, the Al composition X of the n-type intermediate region is equal to or smaller than the Al composition Z of the n-type semiconductor layer, and the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are sequentially arranged on the substrate in the direction of the axis from the n-type intermediate region to the n-electrode.

A third aspect of the present invention is a contact structure for a Group III nitride semiconductor device, the contact structure comprising: a substrate providing a Group III nitride primary surface containing aluminum as a Group III constituent element; a semiconductor region in contact with the Group III nitride primary surface and containing one or more Group III nitride semiconductor layers; an n-type semiconductor layer of a Group III nitride semiconductor in contact with the semiconductor region; an n-type contact layer of a Group III nitride semiconductor containing gallium as a Group III constituent element provided on the n-type semiconductor layer; an n-type intermediate region of a Group III nitride semiconductor containing gallium and aluminum as Group III constituent elements provided on the n-type semiconductor layer; and an n-electrode containing a metal, the Group III nitride semiconductor of the n-type semiconductor layer being I The n-type semiconductor layer contains aluminum as a group II constituent element, and is provided between the substrate and the n-type intermediate region, and the n-type intermediate region is provided between the n-type contact layer and the n-type semiconductor layer, and the n-type contact layer is provided between the n-type intermediate region and the n-electrode, and the group III nitride semiconductor of the n-type intermediate region has an Al composition X that changes monotonically in the direction from the n-type semiconductor layer to the n-electrode, and the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the group III nitride semiconductor of the n-type contact layer, the Al composition Y of the n-type contact layer is equal to or greater than zero, and the Al composition X of the n-type intermediate region is equal to or less than the Al composition Z of the n-type semiconductor layer.

The above aspects of the present invention provide a semiconductor light-emitting device having an n-side contact structure that can provide good electrical characteristics over a wide range of Al compositions, a method for fabricating a semiconductor light-emitting device, and a contact structure.

FIG. 1 is a diagram showing a schematic diagram of a nitride device according to an embodiment of the present invention. FIG. 2 is a diagram showing an example of a nitride device according to the present embodiment. FIG. 3 is a diagram showing a contact structure according to the present embodiment. FIG. 4 is a diagram showing the main steps of a method for fabricating a nitride device according to this embodiment. FIG. 5 is a diagram showing the main steps of a method for fabricating a nitride device according to this embodiment. FIG. 6 is a diagram showing the main steps of a method for fabricating a nitride device according to this embodiment. FIG. 7 is a diagram showing the main steps of a method for fabricating a nitride device according to this embodiment. Fig. 8A is a diagram showing a schematic diagram of an element structure (reference structure) having a contact structure of a direct contact structure, and Fig. 8B is a diagram showing a schematic diagram of a simulation model according to an experimental example. 9A and 9B are diagrams that diagrammatically show a simulation model according to an experimental example. 10A and 10B are graphs showing the results of calculations using the simulation model of FIG. 9A (Al composition of the n-type semiconductor layer: 75%). 11A and 11B are graphs showing the results of calculations using the simulation model of FIG. 8B (Al composition of the n-type semiconductor layer: 75%). 12(a) and 12(b) are graphs showing the voltage rise in an intermediate layer having a thickness of 50 nm in the simulations of FIGS. 10(a) and 10(b), respectively. 13(a) and 13(b) are graphs showing the voltage rise in an intermediate layer having a thickness of 50 nm in the simulations of FIGS. 11(a) and 11(b), respectively. Fig. 14(a) is a diagram showing the electron concentration in a contact structure including a 10 nm thick intermediate layer with graded Al composition, Fig. 14(b) is a diagram showing the electron concentration in a contact structure including a 20 nm thick intermediate layer with graded Al composition, Fig. 14(c) is a diagram showing the electron concentration in a contact structure including a 30 nm thick intermediate layer with graded Al composition, and Fig. 14(d) is a diagram showing the electron concentration in a contact structure including a 50 nm thick intermediate layer with graded Al composition. 15A and 15B are graphs showing the results of calculations using the simulation model of FIG. 9B (Al composition of the n-type semiconductor layer: 90%). 16A and 16B are graphs showing the results of calculations using the simulation model of FIG. 8B (Al composition of the n-type semiconductor layer: 90%). Figures 17(a) and 17(b) are diagrams showing the voltage rise in a 50 nm thick intermediate layer in the simulations of Figures 15(a) and 15(b), respectively. Figures 17(c) and 17(c) are diagrams showing the voltage rise in a 50 nm thick intermediate layer in the simulations of Figures 16(a) and 16(b), respectively. FIG. 18 is a graph showing the results of calculations using the simulation model of FIG. 19(a) and 19(b) are diagrams showing an epitaxial structure of a contact structure and a contact structure for electrical measurement, and FIG. 19(c) and FIG. 19(d) are diagrams showing a contact structure for electrical measurement. 20(a) and 20(b) are diagrams showing the results of electrical measurements of the contact structure shown in FIG. 19(b) (without the intermediate layer). 21(a) and 21(b) are diagrams showing the results of electrical measurements of the contact structure (with grooves) shown in FIG. 19(d). 22(a) and 22(b) are diagrams showing the results of electrical measurements of the contact structure (with intermediate layer) shown in FIG. 19(a). 23(a) and 23(b) are diagrams showing the results of electrical measurements of the contact structure (with grooves) shown in FIG. 19(c). FIG. 24 is a graph showing the dependence of the characteristic contact resistance on the Al composition of the graded Al composition intermediate layer for several intermediate layer thicknesses. FIG. 25 is a diagram showing the measurement results of X-ray diffraction reciprocal space mapping (XRD-RSM) of the epitaxial structure (not including electrodes) shown in FIG. 19(a). 26(a) to 26(f) are drawings showing differential interference contrast microscope images of the epitaxial structure shown in FIG. 19(a). FIG. 27 is a graph showing the current-voltage characteristics of a deep ultraviolet light-emitting diode.

Each embodiment of the present invention will be described below with reference to the drawings. Identical and similar parts are given the same or similar reference numerals, and redundant description will be omitted.

Figure 1 is a diagram showing a schematic diagram of a nitride device according to an embodiment of the present invention. Figure 2 is a diagram showing an example of a nitride device according to an embodiment of the present invention. In Figure 2, a cross-sectional line I-I is drawn, showing a cross section of the device in Figure 1. Figure 3 is a diagram showing a schematic diagram of a contact structure according to an embodiment of the present invention.

A nitride device is a light-emitting device in which an active layer for emitting light comprises a group III nitride, such as a light-emitting diode (LED), a laser diode (LD), or a light source excited by an electron beam, and the n-type semiconductor layer may comprise a group III nitride, and further, if necessary, the p-type semiconductor layer may comprise a group III nitride. However, the nitride device is not limited to a light-emitting device, and may include electronic devices not related to light emission, such as a high electron mobility transistor (HEMT), a photodetector (PD), a surface acoustic wave element, and a piezoelectric element. Group III elements include aluminum (Al), gallium (Ga), and indium (In). Group III nitrides are compounds of one or more group III elements (at least one of Al, Ga, and In) and nitrogen (N).

In the following description, the nitride device 110 has the structure of a light emitting diode, by way of example and not limitation, and the light emitting diode operates as a semiconductor light emitting device.

The nitride device 110 has a contact structure 111, which includes an n-type semiconductor layer 125, an n-type contact layer 127, an n-type intermediate region 129, and an n-electrode 131.

The n-type semiconductor layer 125 includes a group III nitride semiconductor. The group III nitride semiconductor of the n-type semiconductor layer 125 includes aluminum as a group III constituent element. The n-type contact layer 127 is provided on the n-type semiconductor layer 125 and includes a group III nitride semiconductor including gallium as a group III constituent element. The n-type intermediate region 129 is provided on the n-type semiconductor layer 125 and includes a group III nitride semiconductor including gallium and aluminum as group III constituent elements. The n-electrode 131 includes a metal provided on the n-type semiconductor layer 125, the n-type intermediate region 129, and the n-type contact layer 127.

The n-type intermediate region 129 is provided between the n-type contact layer 127 and the n-type semiconductor layer 125. The n-type contact layer 127 is provided between the n-type intermediate region 129 and the n-electrode 131.

The group III nitride semiconductor of the n-type intermediate region 129 can have an Al composition X that varies monotonically in the direction of the axis Ax1 from the n-type semiconductor layer 125 to the n-electrode 131. The monotonically varying Al composition does not increase in the direction from the n-type semiconductor layer 125 to the n-type contact layer 127. The Al composition X of the n-type intermediate region 129 is equal to or greater than the Al composition Y of the group III nitride semiconductor of the n-type contact layer 127, and the Al composition Y of the n-type contact layer 127 is equal to or greater than zero. The Al composition X of the n-type intermediate region 129 is equal to or less than the Al composition Z of the n-type semiconductor layer 125.

In the nitride device 110, the n-type intermediate region 129 having an Al composition X that changes monotonically in the direction from the n-type semiconductor layer 125 to the n-electrode 131 provides good electrical characteristics to the contact structure 111 for providing carriers to the n-type semiconductor layer 125. In the contact structure 111, the n-type intermediate region 129, the n-type contact layer 127, and the n-electrode 131 are arranged in this order. The Al composition Y of the n-type contact layer 127 is equal to or less than the Al composition X of any area of the n-type intermediate region 129. In addition, the Al composition Z of the n-type semiconductor layer 125 is equal to or greater than the Al composition X of any area of the n-type intermediate region 129.

The n-type intermediate region 129 can have at least one of a graded composition GR and a stepwise composition ST, as shown in the Al composition profile Al-P in FIG. 1. The n-type intermediate region 129 may have an Al composition profile that combines the graded composition GR and the stepwise composition ST. In the graded composition GR and the stepwise composition ST, the Al composition X of the n-type intermediate region 129 decreases in the direction from the n-type semiconductor layer 125 to the n-type contact layer 127 in at least a portion of the n-type intermediate region 129. According to the nitride device 110, the graded composition GR and the stepwise composition ST provide a monotonically changing Al composition X in the n-type intermediate region 129.

By way of example and not limitation, the Al composition X of the n-type intermediate region 129 can decrease monotonically throughout the n-type intermediate region 129 in a direction from the n-type semiconductor layer 125 to the n-electrode 131.

Specifically, the n-type intermediate region 129 may include, for example, Al _x Ga _1-x N, and may further include indium as a group III constituent element. The Al composition X of the n-type intermediate region 129 decreases throughout the n-type intermediate region 129 in a direction from the n-type semiconductor layer 125 to the n-type contact layer 127. According to the nitride device 110, the n-type intermediate region 129 has an interface associated with the n-type semiconductor layer 125 and an interface associated with the n-type contact layer 127, and the Al composition X decreases from one of these interfaces to the other.

The Al composition X of the n-type intermediate region 129 has a terminating Al composition at the interface associated with the n-type contact layer 127. The terminating Al composition can be equal to or greater than the Al composition of the n-type contact layer 127 (including an Al composition of zero). By way of example and not limitation, an Al composition difference at this interface, e.g., a composition difference of 30% or less, is acceptable in that the voltage rise at the interface is kept to approximately zero. Also, the terminating Al composition of the n-type intermediate region 129 can be, for example, 20% or more.

The Al composition X of the n-type intermediate region 129 has a starting Al composition at the interface associated with the n-type semiconductor layer 125. The starting Al composition can be equal to or less than the Al composition of the n-type semiconductor layer 125. By way of example and not limitation, the starting Al composition of the n-type intermediate region 129 may be equal to the Al composition of the top surface of the n-type semiconductor layer 125, thereby reducing the change in electron concentration near the interface associated with the n-type semiconductor layer 125. By way of example and not limitation, an Al composition difference at this interface, for example a composition difference of 30% or less, is acceptable in that the voltage rise at the interface is suppressed to approximately zero. In the following description, even if the phrase "by way of example and not by way of limitation" is not used, the numerical values are generally allowed to be within a certain range, and are shown by way of example and not by way of limitation.

The n-type contact layer 127 may include at least one of n-type GaN, n-type AlGaN, and n-type InAlGaN. According to the nitride device 110, the n-type contact layer 127 may be provided with a gallium nitride-based semiconductor such as n-type GaN, n-type AlGaN, or n-type InAlGaN. In this embodiment, the n-type contact layer 127 may be n-type GaN and/or n-type AlGaN, and the Al composition may be 0% to 40%. By way of example and not limitation, the n-type contact layer 127 may have a thickness of, for example, 10 to 1000 nm.

The group III nitride semiconductor of the n-type semiconductor layer 125 may include at least one of AlN, AlGaN, and InAlGaN. According to the nitride device 110, AlN, AlGaN, or InAlGaN may be used as the underlayer of the n-type contact layer 127 and the n-type intermediate region 129. In this embodiment, the n-type semiconductor layer 125 includes n-type AlGaN, and the Al composition may be in the range of 60% to 90%. The Al composition of the upper surface of the n-type semiconductor layer 125 may be in the range of 60% to 90%. The n-type semiconductor layer 125 may have a thickness of, for example, 100 to 5000 nm.

By way of example and not limitation, the nitride device 110 may further include an active layer 114 and a p-type semiconductor layer 121. The active layer 114 and the p-type semiconductor layer 121 are disposed on the n-type semiconductor layer 125 and the substrate 133.

The active layer 114 is capable of generating deep ultraviolet light and includes a group III nitride semiconductor provided on a substrate 133. The wavelength of the deep ultraviolet light can be in the range of 285 nm or less, for example, 200 nm or more.

Specifically, the active layer 114 may consist of a single layer of AlGaN, or may have a single or multiple quantum well structure 114a. Specifically, the well layer 114b may include undoped AlGaN, and the barrier layer 114c may include undoped AlGaN. Either or both of the well layer 114b and the barrier layer 114c may be doped with Si. The AlGaN of the barrier layer 114c has a larger band gap than the AlGaN of the well layer 114b. The barrier layer 114c may include AlN, if desired.

According to the nitride device 110, for deep ultraviolet light with a wavelength of 285 nm or less, an active layer 114 with a high Al composition is required, and the current path to the active layer 114 is also formed by a group III nitride with a high Al composition. A good n-type contact structure 111 to the group III nitride with a high Al composition is provided by the combination of the n-type intermediate region 129, the n-type contact layer 127, and the n-electrode 131.

The n-type intermediate region 129, which has an Al composition X that changes monotonically in the direction from the n-type semiconductor layer 125 to the active layer 114, provides good electrical characteristics to the contact structure 111 for providing carriers to the active layer 114 via the n-type semiconductor layer 125. The Al composition Y of the n-type contact layer 127 is equal to or less than the Al composition X of any area of the n-type intermediate region 129. The Al composition Z of the n-type semiconductor layer 125 is equal to or greater than the Al composition X of any area of the n-type intermediate region 129.

Optionally, the nitride device 110 further comprises a substrate 133 providing a III-nitride primary surface 133a including aluminum as a group III constituent element. The n-type semiconductor layer 125 is disposed between the substrate 133 and the n-type intermediate region 129.

The n-type semiconductor layer 125 may have at least one of a graded composition (structure identical or similar to GR) and a stepwise composition (structure identical or similar to ST) that changes monotonically in the direction from the substrate 133 to the n-type contact layer 127 (or from the n-type contact layer 127 to the n-electrode 131). According to the contact structure 111, the n-type semiconductor layer 125 may have a monotonically changing Al composition, and the monotonically changing Al composition does not increase in the direction from the substrate 133 to the n-type contact layer 127. Also, the monotonically changing Al composition is provided by a graded composition and a stepwise composition in the n-type semiconductor layer 125 having an Al composition equal to or greater than the maximum value of the Al composition X. By way of example and not limitation, the n-type semiconductor layer 125 may have an Al composition that decreases monotonically in the direction from the substrate 133 to the n-type contact layer 127 (or from the n-type contact layer 127 to the n-electrode 131).

By way of example and not limitation, the contact structure 111 can allow the n-type semiconductor layer 125 to have a single Al composition. The technical meaning of "single Al composition" in this case should be determined taking into account the measurement variability of the Al composition, which can be 5% or less, for example, by Auger electron spectroscopy. Alternatively, the nitride device 110 can include a semiconductor region 135 including one or more Group III nitride semiconductor layers, the semiconductor region 135 making contact with the Group III nitride primary surface 133a. The Group III nitride semiconductor of the n-type semiconductor layer 125 makes contact with the primary surface 135a of the semiconductor region 135.

According to the nitride device 110, the active layer 114 is provided on the substrate 133 as described above. The n-type semiconductor layer 125, the active layer 114, and the p-type semiconductor layer 121 are sequentially arranged in the axial direction from the n-type intermediate region 129 to the n-electrode 131.

The substrate 133, the n-type semiconductor layer 125, the active layer 114, and the p-type semiconductor layer 121 are arranged in order along the axis Ax1 extending from the n-type contact layer 127 to the n-electrode 131. In the contact structure 111, the n-type intermediate region 129, the n-type contact layer 127, and the n-electrode 131 are arranged in this order. The contact structure 111 provides good electrical characteristics to the nitride device 110 having the n-type semiconductor layer 125 that is closer to the substrate 133 than the p-type semiconductor layer 121.

The substrate 133 is equipped with an n-type semiconductor layer 125, an active layer 114, a p-type semiconductor layer 121, an n-type contact layer 127, and an n-type intermediate region 129.

In the nitride device 110, the n-type contact layer 127 can have an in-plane lattice constant equal to or greater than the in-plane lattice constant of the n-type intermediate region 129. According to this nitride device 110, the n-type contact layer 127 is provided with a group III nitride that is lattice-relaxed with respect to the n-type intermediate region 129. In addition, the n-type contact layer 127 that is lattice-relaxed with respect to the n-type intermediate region 129 can reduce the electrical resistance at the interface between the n-type contact layer 127 and the n-type intermediate region 129.

When the lattice constant in the in-plane direction of the n-type contact layer 127 is larger than the lattice constant in the in-plane direction of the n-type intermediate region 129, the carrier concentration at the interface between the n-type contact layer 127 and the n-type intermediate region 129 changes. More strictly, in the in-plane direction perpendicular to the axis from the n-type intermediate region 129 to the n-electrode 131, the lattice constant of the n-type contact layer 127 is larger than the lattice constant of the n-type intermediate region 129.

The n-type contact layer 127 can have a lattice relaxation rate of 0.5 or more (50% or more) relative to the n-type semiconductor layer 125. According to the nitride device 110, the n-type contact layer 127 can be provided with a group III nitride having a lattice relaxation rate of 0.5 or more relative to the n-type semiconductor layer 125. The magnitude of the lattice relaxation rate of the n-type contact layer 127 can change the carrier concentration at the interface between the n-type contact layer 127 and the n-type intermediate region 129. In addition, the lattice relaxation rate of the n-type contact layer 127 relative to the n-type semiconductor layer 125 may be greater than the lattice relaxation rate of the n-type intermediate region 129 relative to the n-type semiconductor layer 125.

The substrate 133 may be a substrate containing a group III nitride containing aluminum as a group III constituent element, and may be, for example, a single crystal aluminum nitride substrate. Alternatively, the substrate 133 may include a support 118 and a template layer 120. The support 118 has a main surface 118a made of a material different from the group III nitride. The template layer 120 is made of a group III nitride and is provided on the main surface 118a of the support 118. The template layer 120 may be, for example, an AlN template layer or an AlGaN template layer. The template layer 120 may cover the main surface 118a of the support 118 and may contain compressive strain. This compressive strain may be a source of strain applied to the contact structure 111. The template layer 120 may be, for example, 2000 nm or less, for example, 500 nm.

By way of example and not limitation, the support 118 may include at least one of the following materials: silicon, carbon, boron nitride (BN), aluminum oxide (sapphire), ceramic, silicon carbide, refractory metals, zirconia, tantalum carbide (TaC), ScAlMgO _4. For example, the support 118 may have a hexagonal crystal structure.

The active layer 114 is provided on the substrate 133 so as to generate light having a peak wavelength in the deep ultraviolet wavelength region of 285 nm or less, and may contain AlGaN containing compressive strain.

The nitride device 110 may further include a nitride semiconductor region 116. The nitride semiconductor region 116 is provided between the substrate 133 and the active layer 114, and includes Al as a group III constituent element. The nitride semiconductor region 116 may include one or more n-type group III nitride semiconductor layers, and specifically includes an n-type semiconductor layer 125.

In this embodiment, the nitride semiconductor region 116 may include a first n-type semiconductor layer 122 and a second n-type semiconductor layer 124. The first n-type semiconductor layer 122 is provided between the substrate 133 and the active layer 114, and the second n-type semiconductor layer 124 is provided between the first n-type semiconductor layer 122 and the active layer 114. The n-type semiconductor layer 125 may be either the first n-type semiconductor layer 122 or the second n-type semiconductor layer 124, or both the first n-type semiconductor layer 122 and the second n-type semiconductor layer 124. For example, the first n-type semiconductor layer 122 may be provided between the substrate 133 and the n-type contact layer 127, and the first n-type semiconductor layer 122 may be provided between the substrate 133 and the n-type intermediate region 129.

By way of example and not limitation, the first n-type semiconductor layer 122 can include a Group III nitride such as AlGaN or InAlGaN, and the second n-type semiconductor layer 124 can include a Group III nitride such as AlGaN or InAlGaN.

By way of example and not limitation, the first n-type semiconductor layer 122 can have a first Al composition that is substantially equal to the second Al composition of the second n-type semiconductor layer 124. Alternatively, the first n-type semiconductor layer 122 can have a first Al composition that is greater than the second Al composition of the second n-type semiconductor layer 124.

By way of example and not limitation, the thickness of the first n-type semiconductor layer 122 may be greater than the thickness of the second n-type semiconductor layer 124. The thickness of the nitride semiconductor region 116 may be, for example, 200 to 3000 nm. The thickness of the second n-type semiconductor layer 124 may be 10 to 200 nm, and preferably 50 to 150 nm.

The nitride device 110 has a lower III-nitride stack 113 located between the active layer 114 and the substrate 133, and an upper III-nitride stack 115 located above the active layer 114.

In this embodiment, the lower group III nitride stack 113 forms a bond 119a with the substrate 133 and can contain compressive strain due to both or at least one of the compressive strain contained in the group III nitride of the substrate 133 and the lattice constant difference between the group III nitride of the substrate 133 and the lower group III nitride stack 113. The lower group III nitride stack 113 also forms a bond 119b with the active layer 114. The active layer 114 can contain compressive strain due to both or at least one of the compressive strain contained in the group III nitride of the substrate 133 and the lattice constant difference between the group III nitride of the substrate 133 and the active layer 114. Meanwhile, a part or all of the upper group III nitride stack 115 may be lattice-relaxed. The upper group III nitride stack 115 is provided on the active layer 114 and supplies carriers to the active layer 114.

The lower III-nitride stack 113 may include one or more III-nitride semiconductor layers in addition to the nitride semiconductor region 116. Specifically, the lower III-nitride stack 113 may include a semiconductor region 135. The semiconductor region 135 may include an underlayer, specifically an Al _U Ga _1-U N layer 130 (where U is greater than zero and equal to or greater than X and equal to or less than 1). The _{Al U} Ga _1- U N layer 130 may be, for example, undoped, and may be provided to cover the substrate 133.

The lower III-nitride stack 113 (and the semiconductor region 135) may include another underlayer, specifically, another _{Al.sub.VGa.sub.1 -VN} layer 132 (where V is less than 1 and greater than 0.8, and V is less than U). The _{Al.sub.VGa.sub.1 -} VN layer 132 may be, for example, undoped, and may be provided on the _{Al.sub.UGa.sub.1 -UN} layer 130.

In this embodiment, the nitride semiconductor region 116 forms a junction 119c with the Al _V Ga _1-V N layer 132 (primary surface 135a of the semiconductor region 135). The Al _V Ga _1-V N layer 132 forms a junction 119d with the Al _U Ga _1-U N layer 130. In addition to the nitride semiconductor region 116, the lower group III nitride stack 113 is provided with an Al _U Ga _1-U N layer 130 and an Al _V Ga _1-V N layer 132. The nitride semiconductor region 116 has an Al composition smaller than the Al composition of the Al _V Ga 1- _V N layer 132 and larger than the Al composition of the well layer 114b.

The lower group III nitride stack 113 has an Al composition profile Al-P that changes monotonically in the direction from the substrate 133 to the n-electrode 131. The monotonically changing Al composition profile Al-P means that when the Al composition of the primary surface of the substrate 133 is greater than the Al composition of the well layer 114b, the Al composition of the lower group III nitride stack 113 does not increase from the substrate 133 to the active layer 114.

Next, the upper III-nitride stack 115 will be described. The upper III-nitride stack 115 may include, for example, an electron block layer 134, a p-type graded composition layer 136, and a p-type contact layer 138. The electron block layer 134, the p-type graded composition layer 136, and the p-type contact layer 138 (138a, 138b) may be provided in order on the active layer 114. When the electron block layer 134 is undoped, the p-type graded composition layer 136 and the p-type contact layer 138 function as the p-type semiconductor layer 121.

By way of example and not limitation, the upper III-nitride stack 115 may have the following configuration:
Electron blocking layer 134: undoped or Mg-doped AlN, thickness 7 nm.
p-type graded composition layer 136: undoped or Mg-doped graded composition AlGaN (Al composition: 0.9 to 0.4), thickness 15 nm.
P-type contact layer 138a (first layer): Mg-doped GaN, thickness 120 nm.
p-type contact layer 138b (second layer): Highly Mg-doped GaN, thickness 30 nm.

The nitride device 110 has an etched region 142. The etched region 142 can include the upper group III nitride stack 115, the active layer 114, and the upper side of the nitride semiconductor region 116 (specifically, the upper side of the second n-type semiconductor layer 124 or the upper sides of the second n-type semiconductor layer 124 and the first n-type semiconductor layer 122). In this embodiment, as shown in FIG. 2, the upper surface of the etched region 142 can have a comb shape.

The nitride device 110 may further include a passivation film 144, which covers the etched region 142 and the nitride semiconductor region 116. The passivation film 144 has a first opening 144a located on the upper surface of the etched region 142 and a second opening 144b located on the upper surface of the n-type contact layer 127. The passivation film 144 may include, for example, _aluminum oxide ( _Al2O3 ), AlSiO, or a silicon-based inorganic insulator. The silicon-based inorganic insulator may include, for example, _silicon oxide (e.g., _SiO2 ), silicon nitride (e.g., _Si3N4 ), or silicon oxynitride (e.g., SiON).

The nitride device 110 can have a p-electrode 146. The p-electrode 146 is disposed within the first opening 144a, and the n-electrode 131 is disposed within the second opening 144b. The p-electrode 146 makes contact with an upper surface of the p-contact layer 138. The n-electrode 131 makes contact with an upper surface of the n-contact layer 127. By way of example and not limitation, the n-electrode 131 can include Ti/Al/Ni/Au (meaning that Ti, Al, Ni, and Au are stacked in this order), and the p-electrode 146 can include Ni/Au (meaning that Au is stacked on Ni). In this embodiment, as shown in FIG. 2, the upper surface of the n-electrode 131 can have an interdigitated shape, and the upper surface of the p-electrode 146 can have an interdigitated shape.

The n-type semiconductor layer 125 includes a first region 125a and a second region 125b. The first region 125a and the second region 125b are arranged along a reference plane Ref that intersects with an axis Ax1 from the n-type intermediate region 129 to the n-type contact layer 127. The active layer 114 and the p-type semiconductor layer 121 are provided on the second region 125b, not on the first region 125a. The n-electrode 131, the n-type contact layer 127, and the n-type intermediate region 129 are provided on a part of the first region 125a, not on the second region 125b. According to the nitride device 110, the n-type contact layer 127 and the n-type intermediate region 129 are selectively provided on the first region 125a, and the n-type contact layer 127 and the n-type intermediate region 129 are used to contact the n-electrode 131.

Figures 4(a), 4(b), 5(a), 5(b), 6(a), 6(b), 7(a), and 7(b) are diagrams showing the main steps of a method for fabricating a nitride device 110 according to this embodiment. In the following description of the fabrication method, a light-emitting diode structure is fabricated as the nitride device 110. The light-emitting diode structure of the nitride device 110 includes an n-type semiconductor layer 125, an active layer 114, and a p-type semiconductor layer 121, and the active layer 114 includes a group III nitride semiconductor capable of generating deep ultraviolet light. The n-type semiconductor layer 125, the active layer 114, and the p-type semiconductor layer 121 are sequentially arranged on the substrate 133 in the direction of the axis Ax from the n-type intermediate region 129 toward the n-electrode 131.

As shown in the process of FIG. 4(a), an epitaxial wafer 162 is prepared. Preparing the epitaxial wafer 162 includes, for example, fabricating the epitaxial wafer 162 or obtaining the epitaxial wafer 162 by a method other than fabrication.

Fabricating the epitaxial wafer 162 can include the following steps:

In the process of FIG. 4A, an epitaxial wafer 162 is fabricated. A substrate 150 for fabricating the epitaxial wafer 162 is prepared. The substrate 150 can be, for example, an AlN template including a 2-inch sapphire substrate. To fabricate the epitaxial wafer 162, a III-nitride stack 164 including a plurality of III-nitride films is grown on the substrate 150. This growth can be performed by, for example, a metalorganic vapor phase epitaxy (MOVPE) method or a molecular beam epitaxy (MBE) method. In the following description, an MOVPE reactor 155a is employed, and trimethylgallium (TMGa) and trimethylaluminum (TMAl) are used as the gallium precursor and the aluminum precursor, respectively. _NH3 is used as the nitrogen source.

The III-nitride stack 164 includes a semiconductor film for the lower III-nitride stack 113 and the active layer 114. Specifically, the III-nitride stack 164 has a nitride semiconductor region 166 and an active layer 168.

A nitride semiconductor region 166 is grown on the substrate 150. The nitride semiconductor region 166 includes a group III nitride semiconductor containing compressive strain. Specifically, a first n-type semiconductor layer 165 is grown on the substrate 150, and a second n-type semiconductor layer 167 is grown on the first n-type semiconductor layer 165. Each of the first n-type semiconductor layer 165 and the second n-type semiconductor layer 167 includes an n-type dopant (e.g., silicon) in this embodiment. In this embodiment, the first n-type semiconductor layer 165 is prepared as a semiconductor film for the n-type semiconductor layer 125.

After growth of the nitride semiconductor region 166, the active layer 168 is grown. Specifically, the active layer 168 can include AlGaN. The active layer 168 can be configured to generate light having a peak wavelength in the deep ultraviolet wavelength region of 285 nm or less. By way of example and not limitation, the active layer 168 can generate light, for example, in the deep ultraviolet wavelength region up to about 200 nm. By way of example and not limitation, the active layer 168 can include InAlGaN, which can generate light in the deep ultraviolet wavelength region.

A nitride semiconductor region 166 and an active layer 168 are grown on the substrate 150 to form the following structure. The nitride semiconductor region 166 includes a first n-type semiconductor layer 165 and a second n-type semiconductor layer 167. The first n-type semiconductor layer 165 is disposed between the substrate 150 and the active layer 168, and the second n-type semiconductor layer 167 is disposed between the first n-type semiconductor layer 165 and the active layer 168. By way of example and not limitation, the second n-type semiconductor layer 167 may have a thickness less than the thickness of the first n-type semiconductor layer 165.

The active layer 168 may have a quantum well structure 168a, as previously described. The quantum well structure 168a of the active layer 168 includes one or more well layers 168b and one or more barrier layers 168c.

The active layer 168 is grown on the nitride semiconductor region 166. Specifically, the active layer 168 has a structure including an AlGaN well layer 168b and an AlGaN barrier layer 168c that are alternately stacked. The AlGaN well layer 168b and the AlGaN barrier layer 168c each contain AlGaN having an Al composition. Specifically, the Al composition of the AlGaN well layer 168b is smaller than the Al composition of the AlGaN barrier layer 168c. The thickness of the AlGaN well layer 168b may be 0.5 to 3.0 nm, and more preferably 1.0 to 2.5 nm. The number of layers of the AlGaN well layer 168b may be, for example, three. The top layer of the active layer 168 may be the AlGaN well layer 168b, and therefore an electron block layer 174 may be in contact with the active layer 168. The AlGaN well layers 168b may have the same thickness and Al composition, or may have different thicknesses and Al compositions. For example, the top AlGaN well layer 168b of the active layer 168 is in contact with the electron block layer 174, and this AlGaN well layer 168b may have a smaller thickness than the other AlGaN well layers 168b. The emission wavelength of the active layer 168 may be 200 to 285 nm, and more preferably 255 to 285 nm. The AlGaN well layer 168b may have a thickness of 2 nm, an Al composition of 0.42, and a Si dopant concentration of 3×10 ¹⁷ cm ⁻³ . The AlGaN barrier layer 168c may have a thickness of 3 nm, an Al composition of 0.66, and a Si dopant concentration of 5×10 ¹⁷ cm ⁻³ .
Examples of growth conditions for AlGaN in the active layer 168:
Growth pressure: 40 kPa
Substrate temperature: 1050 degrees Celsius

By way of example and not limitation, the thickness of the first n-type semiconductor layer 165 can be 800 nm or more, and the thickness of the second n-type semiconductor layer 167 can be less than 200 nm. The nitride semiconductor region 166 provides the growth of the active layer 168 with low dislocation density and good planarity derived from the substrate 150.

In this embodiment, one or more Group III nitride semiconductor layers can be grown prior to the growth of the nitride semiconductor region 166 and the active layer 168. In the Group III nitride stack 164, specifically, the semiconductor region 171 for the lower Group III nitride stack 113 can include the following semiconductor layers in addition to the nitride semiconductor region 166:

Specifically, an Al _U Ga _1-U N layer 170 (where U is greater than zero and equal to or greater than X and equal to or less than 1) may be grown to cover the substrate 150. The _{Al U} Ga _1-U N layer 170 has an Al composition greater than the Al composition of the nitride semiconductor region 166. By way of example and not limitation, the Al _U Ga _1-U N layer 170 may be undoped. Additionally, the Al _U Ga _1-U N layer 170 may include compressive strain.

Specifically, another _{Al.sub.V Ga.sub.1 -V} N layer 172 (V is less than 1 and greater than 0.8; V is less than U) can be grown on the Al.sub.U _Ga.sub.1-U N layer 170. The _Al.sub.V Ga.sub.1 _-V N layer 172 has an Al composition greater than the Al composition of the nitride semiconductor region 166. The _Al.sub.V Ga.sub.1 _-V N layer 172 can include compressive strain.

The III-nitride stack 164 may include, in addition to the nitride semiconductor region 166 and the active layer 168 , an undoped Al _U Ga _1-U N layer 170 and an undoped Al _V Ga _1-V N layer 172 .

Subsequently, a plurality of III-nitride semiconductor layers 163 for the upper III-nitride stack 115 are grown on the active layer 168. Specifically, an electron block layer 174, a p-type graded composition layer 176, and a p-type contact layer 178 can be grown, in order, on the active layer 168. The III-nitride stack 164 can include the electron block layer 174, the p-type graded composition layer 176, and the p-type contact layer 178.

By this growth, epitaxial wafer 162 was produced.

In the step of FIG. 4(b), if necessary, a groove 180a that defines the outer edge of the element of the light-emitting device is formed in the epitaxial wafer 162 by photolithography and etching. Etching is performed from the upper surface of the group III nitride stack 164 to the substrate 150, forming the groove 180a.

5(a), an etching process region 182 is formed in the epitaxial wafer 162 by photolithography and etching to produce a substrate product SP1. Etching is performed from the upper surface of the III-nitride stack 164 to reach the nitride semiconductor region 166 (n-type semiconductor layer 125, or the first n-type semiconductor layer 165, or the second n-type semiconductor layer 167) so as to separate the active layer 168. The etching process region 182 is defined by a groove 180b. The groove 180b separates the multiple III-nitride semiconductor layers 163 and the active layer 168 for the upper III-nitride stack 115. By way of example and not limitation, the first n-type semiconductor layer 165 may appear at the bottom of the groove 180b. The second n-type semiconductor layer 167 may appear at the bottom of the groove 180b instead of the first n-type semiconductor layer 165.

In this embodiment, a group III nitride semiconductor film for the n-type intermediate region 169 and the n-type contact layer 171 is grown on the first n-type semiconductor layer 165 or the second n-type semiconductor layer 167. Specifically, the group III nitride semiconductor films for the n-type intermediate region 169 and the n-type contact layer 171 are formed by selective growth. In the following explanation, crystal growth using the MOVPE reactor 155b is adopted.

In the step of FIG. 5B, a hard mask 173 for selective growth is formed on the substrate product SP1. The hard mask 173 includes a dielectric film, which is formed by a deposition method such as plasma CVD, thermal CVD, or sputtering. The dielectric film includes aluminum oxide (Al ₂ O ₃ ), AlSiO, or a silicon-based inorganic insulator. The silicon-based inorganic insulator may include, for example, silicon oxide (e.g., SiO ₂ ), silicon nitride (e.g., Si ₃ N ₄ ), or silicon oxynitride (e.g., SiON). The hard mask 173 has an opening 173a located at the bottom of the groove 180b. For example, the hard mask 173 is fabricated by depositing an inorganic film and processing the inorganic film by photolithography and etching.

5(b), after forming the hard mask 173, the substrate product SP1 is placed in the MOVPE reactor 155b to grow the n-type intermediate region 169 with a graded Al composition. The n-type intermediate region 169 is deposited on the III-nitride surface at the opening 173a of the hard mask 173. This deposition causes the n-type intermediate region 169 to bond to the underlying first n-type semiconductor layer 165 or second n-type semiconductor layer 167. In this growth, the supply amounts of the gallium precursor and the aluminum precursor are changed. Specifically, the gallium precursor, for example, trimethylgallium, is gradually increased; the aluminum precursor, for example, trimethylaluminum, is gradually decreased; or both. The Al composition of the n-type intermediate region 169 decreases in the direction from the nitride semiconductor region 166 to the active layer 168 (the direction of the axis Ax1 shown in FIG. 1). An n-type dopant is added during the growth.

6(a), after forming the hard mask 173, in this embodiment, the growth of the n-type contact layer 171 is performed consecutively to the growth of the n-type intermediate region 169. The n-type contact layer 171 is deposited on the n-type intermediate region 169 in the opening 173a of the hard mask 173. This deposition causes the n-type contact layer 171 to bond to the n-type intermediate region 169. The n-type contact layer 171 is typically n-type GaN or n-type AlGaN. The Al composition of the n-type contact layer 171 is equal to or greater than zero and equal to or less than the minimum Al composition of the n-type intermediate region 169. An n-type dopant is added during the growth.

6(b), the selective growth of the n-type intermediate region 169 and the n-type contact layer 171 is completed, and then the substrate is removed from the MOVPE reactor 155b. The hard mask 173 is removed by wet etching. A stack 175 of the n-type intermediate region 169 and the n-type contact layer 171 is left at the bottom of the groove 180b. This stack 175 is separated from the etching region 182, and forms a junction J1 with the first n-type semiconductor layer 165 or the second n-type semiconductor layer 167. Within the stack 175, the n-type contact layer 171 forms a junction J2 with the n-type intermediate region 169.

7(a), if necessary, a passivation film 184 is formed by a deposition method such as plasma CVD, thermal CVD, or sputtering. The passivation film 184 is produced by depositing an inorganic film and processing the inorganic film by photolithography and etching. The passivation film 184 has a first opening 184a located on the upper surface of the processed region 182 by etching, and a second opening 184b located on the upper surface of the stack 175 of the n-type intermediate region 169 and the n-type contact layer 171, i.e., on the upper surface of the n-type contact layer 171. The passivation film 184 can include, for example, a silicon-based inorganic insulator.

7B, after selective growth, electrodes, specifically, a p-electrode 186 and an n-electrode 188 are formed. The p-electrode 186 is formed in the first opening 184a, and a heat treatment is performed after the formation. The n-electrode 188 is formed in the second opening 184b, and a heat treatment is performed after the formation. The n-electrode 188 can be formed following the formation of the p-electrode 186, or the p-electrode 186 can be formed following the formation of the n-electrode 188. The n-electrode 188 is in contact with the upper surface of the stack 175 of the n-type intermediate region 169 and the n-type contact layer 171, that is, the n-type contact layer 171. The n-electrode 188 can include a stack structure such as Ti/Au, Ti/Al/Ti/Au, Ti/Al/Ni/Au, V/Al/V/Au, or V/Al/Ni/Au. The p-electrode can include materials such as Ni/Au and ITO.

These steps produce an example of a nitride device 110.

According to this fabrication method, the n-type intermediate region 169 having a monotonically changing Al composition X provides good electrical characteristics to the contact structure for providing carriers to the active layer 168 via the nitride semiconductor region 166 for the n-type semiconductor layer 125.

The Al composition Y of the n-type contact layer 171 is equal to or less than the Al composition X of any area of the n-type intermediate region 169. The Al composition Z of the nitride semiconductor region 166 for the n-type semiconductor layer 125 is equal to or greater than the Al composition X of any area of the n-type intermediate region 169.

Example 1
A simulation relating to the contact structure 111 will be described.

Figure 8(a) is a diagram that shows a schematic of an element structure (reference structure) having a contact structure with a direct contact structure. Figure 8(b) is a diagram that shows a schematic of a simulation model related to an experimental example. Figure 9(a) is a diagram that shows a schematic of a simulation model related to an experimental example. The simulation model related to the experimental example shown in Figure 9(a) differs from the simulation model in Figure 9(b) in that the n-type contact layer is GaN.

The element structure of the simulation model in FIG. 9(a) differs from the element structure shown in FIG. 8(a) in that a contact layer (n-GaN) and an intermediate layer with graded Al composition (n-AlGaN, Al composition: 0%-75% or 0%-90%) are placed between the n-electrode and the underlying n-type AlGaN (Al composition: 75% or 90%). The element structure of the simulation model in FIG. 8(b) differs from the element structure shown in FIG. 9(a) in that an intermediate layer with a constant Al composition (n-AlGaN, Al composition: 0%-70% or 0%-80%) is placed instead of the intermediate layer with graded Al composition (n-AlGaN, Al composition: 0%-75% or 0%-90%). The intermediate layer with graded Al composition has a starting Al composition value at the interface with the underlying n-type AlGaN and a terminal Al composition value at the interface with the contact layer. The graded Al composition of this intermediate layer decreases linearly from the starting Al composition value to the terminal Al composition value. In the element structure of the simulation model in FIG. 9(a), the n-electrode makes contact with the contact layer (n-GaN). This contact layer makes contact with an intermediate layer with graded Al composition (n-type AlGaN, Al composition: 0% to 75% or 0% to 90%). This intermediate layer makes contact with the underlying n-type AlGaN (Al composition: 75% or 90%).

The results shown subsequently are the voltage difference between the voltage required to pass a current of 100 A/cm2 between the n-electrode and the p-electrode of the device structure of each simulation model shown in Figures 8(b), 9(a), and 9(b) and the voltage required to pass a current of 100 A/cm2 between the n-electrode and the p-electrode of the device structure (reference structure) having the contact structure of the direct contact structure shown in Figure 8(a). In the device structure (reference structure) having the contact structure of the direct contact structure shown in Figure 8(a), the current is injected from the p-electrode and flows into the n-electrode through the p-type layer, the active layer, and the underlying n-type AlGaN. In the device structures of each simulation model shown in Figures 8(b), 9(a), and 9(b), the current is injected from the p-electrode and flows into the n-electrode through the p-type layer, the active layer, the underlying n-type AlGaN, and further through the intermediate layer and the contact layer having a graded Al composition or a constant Al composition. Therefore, in the element structures of the simulation models shown in FIG. 8(b), FIG. 9(a), and FIG. 9(b), the voltage required to pass a current of 100 A/cm 2 between the n-electrode and the p-electrode is higher than that of the element structure (reference structure) having the direct contact structure shown in FIG. 8(a) due to the presence of the contact resistance at the interface between the underlying n-type AlGaN and the intermediate layer of graded Al composition or constant Al composition, the resistance in the intermediate layer of graded Al composition or constant Al composition, the contact resistance at the interface between the intermediate layer ^of graded Al composition or constant Al composition and the contact layer, and the resistance in the contact layer. This voltage increase is the voltage difference shown as the calculation result of the simulation model. In both the reference structure and the element structure of the simulation model, the contact resistance between the n-electrode and the underlying n-type AlGaN, the contact resistance between the n-electrode and the contact layer, and the contact resistance between the p-electrode and the p-type layer are set to zero.

Figures 10(a) and 10(b) are graphs showing the calculation results of the simulation model of Figure 9(a). The Al composition of the underlying n-type AlGaN is 75%. Figures 11(a) and 11(b) are graphs showing the calculation results of the simulation model of Figure 8(b). The Al composition of the underlying n-type AlGaN is 75%. The simulations of Figures 10(a) and 11(a) use a model in which the intermediate layer is grown coherently with respect to the underlying n-type AlGaN. The simulations of Figures 10(b) and 11(b) use a model in which the intermediate layer is grown with complete relaxation (lattice relaxation rate 100%) with respect to the underlying n-type AlGaN. In Figures 10(a) and 10(b), the vertical axis of the graph indicates the terminal Al composition value of the intermediate layer, and the horizontal axis indicates the film thickness of the intermediate layer. In the simulation model, the starting Al composition value is 75%. In Figures 11(a) and 11(b), the vertical axis of the graph indicates the constant Al composition of the intermediate layer, and the horizontal axis indicates the film thickness of the intermediate layer. The graphs in Figures 10(a) to 11(b) show multiple solid lines with numbers. The numbers represent the voltage difference.

Comparing Figures 10(a) and 10(b) with Figures 11(a) and 11(b), the contact structure according to the embodiment in which the intermediate layer has a graded Al composition shows a low voltage rise when the terminal Al composition of the graded Al composition intermediate layer is from zero to a wide Al composition range. Specifically, in the result of Figure 11(a), no area with a voltage of 0.5 volts or less occurs. In the result of Figure 11(b), the area with a voltage of 0.5 volts or less occurs only in a narrow Al composition range where the intermediate layer with a constant Al composition is thin in thickness.

According to FIG. 10(a), which shows a structure in which the intermediate layer with graded Al composition grows coherently with respect to the underlying n-type AlGaN, in a structure in which the contact layer is n-GaN, the contact structure according to the embodiment shows a low voltage rise in a wide range of Al composition from zero for the terminal Al composition of the intermediate layer with graded Al composition. By way of example and not limitation, the range of voltage rise of 3.0 volts or less is for the thickness of the intermediate layer of 15 nm or more. Also, the terminal value of the Al composition of the intermediate layer is in the range of zero to 60%. The range of voltage rise of 0.5 volts or less is for the thickness of the intermediate layer of 30 nm or more. Also, the terminal value of the Al composition of the intermediate layer is in the range of zero to 40%.

According to FIG. 10(b), which shows a structure in which the intermediate layer with graded Al composition is grown with complete relaxation relative to the underlying n-type AlGaN, similarly, in a structure in which the contact layer is n-GaN, the contact structure according to the embodiment shows a low voltage rise in a wide range of Al composition from zero for the terminal Al composition of the intermediate layer with graded Al composition. By way of example and not limitation, the range of voltage rise of 3.0 volts or less is for the thickness of the intermediate layer of 5 nm or more. Also, the terminal value of the Al composition of the intermediate layer is in the range of zero to 45%. The range of voltage rise of 0.5 volts or less is for the thickness of the intermediate layer of 20 nm or more. Also, the terminal value of the Al composition of the intermediate layer is in the range of zero to 20%.

Figures 12(a) and 12(b) show the voltage rise in a 50 nm thick intermediate layer in the simulations of Figures 10(a) and 10(b), respectively. Figures 13(a) and 13(b) show the voltage rise in a 50 nm thick intermediate layer in the simulations of Figures 11(a) and 11(b), respectively. In Figures 12(a) and 12(b), the vertical axis of the graph shows the voltage rise value, and the horizontal axis shows the terminal Al composition value of the graded Al composition intermediate layer. In Figures 13(a) and 13(b), the vertical axis of the graph shows the voltage rise value, and the horizontal axis shows the constant Al composition of the intermediate layer.

In Figures 12(a) and 12(b), the minimum voltage rise is 0.014 volts and 0.015 volts, respectively, and is almost constant in the range of low termination Al composition values (40% or less in Figure 12(a) and 20% or less in Figure 12(b)). On the other hand, in Figures 13(a) and 13(b), the minimum voltage rise is 0.788 volts and 0.767 volts, respectively. For an intermediate layer with a constant Al composition, the voltage rise graph has a downward convex shape.

14(a), 14(b), 14(c) and 14(d) are diagrams showing carrier (electron) concentrations in contact structures including intermediate layers with graded Al composition of 10 nm, 20 nm, 30 nm and 50 nm thickness in the model of FIG. 10(a), respectively. The externally applied voltage is zero, and therefore the current flowing between the n-electrode and the p-electrode is 0 A/cm ^2. In each graph, the terminal value of the Al composition is zero. In FIG. 14(a), in the region of the intermediate layer with graded Al composition, electron depletion occurs corresponding to about 1.3 eV in terms of energy. In FIG. 14(b), in the region of the intermediate layer with graded Al composition, electron depletion occurs corresponding to about 0.8 eV in terms of energy. In FIG. 14(c), slight electron depletion occurs in the region of the intermediate layer with graded Al composition. In FIG. 14(d), substantially no electron depletion occurs in the region of the intermediate layer with graded Al composition.

Figures 15(a) and 15(b) are graphs showing the calculation results of the simulation model of Figure 9(a). The Al composition of the underlying n-type AlGaN is 90%. Figures 16(a) and 16(b) are graphs showing the calculation results of the simulation model of Figure 8(b). The Al composition of the underlying n-type AlGaN is 90%. The simulations of Figures 15(a) and 16(a) use a model in which the intermediate layer is grown coherently with respect to the underlying n-type AlGaN. The simulations of Figures 15(b) and 16(b) use a model in which the intermediate layer is grown with complete relaxation (lattice relaxation rate 100%) with respect to the underlying n-type AlGaN. In Figures 15(a) and 15(b), the vertical axis of the graph indicates the terminal Al composition value of the intermediate layer, and the horizontal axis indicates the film thickness of the intermediate layer. In the simulation model, the starting Al composition value is 90%. In Figures 16(a) and 16(b), the vertical axis of the graph indicates the constant Al composition of the intermediate layer, and the horizontal axis indicates the film thickness of the intermediate layer. The graphs in Figures 15(a) to 16(b) show multiple solid lines with numbers. The numbers represent the voltage difference.

Comparing Figures 15(a) and 15(b) with Figures 16(a) and 16(b), respectively, the contact structure according to the embodiment shows a low voltage rise over a wide range of Al compositions from zero. Specifically, in the results of Figure 16(a), there is no area where the voltage rise is below 2.5 volts. In the results of Figure 16(b), the area where the voltage is below 2.5 volts occurs only in a narrow range of Al compositions where the intermediate layer with a constant Al composition is thin in thickness.

According to FIG. 15(a), which shows a structure in which the intermediate layer with graded Al composition grows coherently with respect to the underlying n-type AlGaN, in a structure in which the contact layer is n-GaN, the contact structure according to the embodiment shows a low voltage rise in a wide range of Al compositions from zero for the terminal Al composition of the intermediate layer with graded Al composition. By way of example and not limitation, the range of voltage rise of 3.0 volts or less is for the thickness of the intermediate layer of 30 nm or more, and the terminal value of the Al composition of the intermediate layer is in the range of zero% to 55%. The range of voltage rise of 1.0 volts or less is for the thickness of the intermediate layer of 35 nm or more, and the terminal value of the Al composition of the intermediate layer is in the range of zero% to 45%.

According to FIG. 15(b), which shows a structure in which the intermediate layer with graded Al composition is grown completely relaxed with respect to the underlying n-type AlGaN, similarly, in a structure in which the contact layer is n-GaN, the contact structure according to the embodiment shows a low voltage rise in a wide range of Al composition from zero for the terminal Al composition of the intermediate layer with graded Al composition. By way of example and not limitation, the range of voltage rise of 3.0 volts or less is 10 nm or more for the film thickness of the intermediate layer. Also, the terminal value of the Al composition of the intermediate layer is in the range of zero% to 30%. The range of voltage rise of 1.0 volts or less is 25 nm or more for the film thickness of the intermediate layer. Also, the terminal value of the Al composition of the intermediate layer is in the range of zero% to 20%.

The carrier concentration (not shown) of the contact structure (coherent growth) at several film thicknesses on the graph shown in Figure 10 (a) was investigated. In the contact structure including an intermediate layer with a thickness of 20 nm and a graded Al composition of 0% at the end, a decrease in the electron concentration occurs in the region of the intermediate layer with the graded Al composition, which corresponds to a value exceeding 0.8 eV in terms of energy. In the contact structure including an intermediate layer with a thickness of 20 nm and a graded Al composition of 20% at the end, a slight decrease in the electron concentration occurs in the region of the intermediate layer with the graded Al composition, which corresponds to about 0.4 eV in terms of energy.

The carrier concentration (not shown) of the contact structure (fully relaxed growth) at several film thicknesses on the graph shown in Figure 10 (b) was investigated. In the contact structure including an intermediate layer with a thickness of 20 nm and a graded Al composition of 0% at the end, the change in electron concentration in the region of the intermediate layer with the graded Al composition corresponds to about 0.2 eV in terms of energy, and there is essentially no decrease in the electron concentration (almost no electron depletion). In the contact structure including an intermediate layer with a thickness of 20 nm and a graded Al composition of 20% at the end, there is slight electron depletion in the region of the intermediate layer with the graded Al composition, corresponding to about 0.4 eV in terms of energy.

Figures 17(a) and 17(b) show the voltage rise in a 50 nm thick intermediate layer in the simulations of Figures 15(a) and 15(b), respectively. Figures 17(c) and 17(d) show the voltage rise in a 50 nm thick intermediate layer in the simulations of Figures 16(a) and 16(b), respectively. In Figures 17(a) and 17(b), the vertical axis of the graph shows the voltage rise value, and the horizontal axis shows the terminal Al composition value of the graded Al composition intermediate layer. In Figures 17(c) and 17(d), the vertical axis of the graph shows the voltage rise value, and the horizontal axis shows the constant Al composition of the intermediate layer.

In Figures 17(a) and 17(b), the minimum values of the voltage rise are both 0 volts, and are almost constant in the range of low termination Al composition values (40% or less in Figure 17(a) and 20% or less in Figure 17(b)). On the other hand, in Figures 17(c) and 17(d), the minimum values of the voltage rise are 2.70 volts and 2.52 volts, respectively. For intermediate layers with constant Al composition, the voltage rise graph has a downward convex shape.

Figure 9(b) is a schematic diagram of a simulation model according to an experimental example. The device structure of the simulation model in Figure 9(b) differs from the device structure shown in Figure 9(a) in that the contact layer is AlGaN. In response to this replacement, the intermediate layer (n-type AlGaN) with a graded Al composition has an Al composition range of 40% to 75%. The graded Al composition of this intermediate layer decreases linearly from the starting Al composition value to the ending Al composition value. The Al composition of the contact layer is 40%. In the device structure of the simulation model in Figure 9(b), the n-electrode makes contact with the contact layer (n-AlGaN). This contact layer makes contact with the intermediate layer with a graded Al composition. This intermediate layer makes contact with the underlying n-type AlGaN (Al composition: 75%).

Figure 18 is a graph showing the calculation results of the simulation model of Figure 9 (b). The simulation of Figure 18 uses a model in which the intermediate layer and contact layer are grown coherently with respect to the underlying n-type AlGaN. In Figure 18, the vertical axis of the graph shows the end value of the Al composition of the intermediate layer, and the horizontal axis shows the film thickness of the intermediate layer. The graph of Figure 18 shows multiple solid lines with numbers. The numbers represent voltage differences. In the simulation model, the starting Al composition value is 75%. The Al composition of the underlying n-type AlGaN is 75%.

According to the graph of FIG. 18 showing a structure in which the intermediate layer with graded Al composition grows coherently with respect to the underlying n-type AlGaN, in a structure in which the contact layer is n-AlGaN, the contact structure according to the embodiment shows a low voltage rise in a wide Al composition range from 40% Al composition. By way of example and not limitation, the range in which the voltage rise is 1 volt or less is 3 nm or more for the film thickness of the intermediate layer. Also, the terminal value of the Al composition of the intermediate layer is in the range of 40% to 60%. When the thickness of the intermediate layer with graded composition is 15 nm or more, the voltage upper layer is almost zero. As a reference value, in a structure in which an AlGaN contact layer with 40% Al composition grows coherently with the underlying n-type AlGaN with 75% Al composition to form a direct bond, a voltage rise of about 1.3 volts occurs. By way of example and not limitation, in a structure in which the contact layer is n-type AlGaN, the terminal value of the Al composition of the intermediate layer can be the same value as the Al composition value of the contact layer and can be a value greater than the Al composition value of the contact layer. In addition, the starting value of the Al composition of the intermediate layer can be the same as the Al composition value of the underlying n-type AlGaN, or can be a smaller Al composition value than the Al composition value of the underlying n-type AlGaN.

In the simulation model structure of Figure 9(b), the emission wavelength of the active layer is, for example, 280 nm. The n-electrode uses a structure in which Al, which has a high reflectivity for deep ultraviolet light, is in direct contact with the contact layer. Since the Al composition of the contact layer is 40%, the contact layer is transparent to light with a wavelength of 280 nm. A portion of the deep ultraviolet light emitted from the active layer passes through the contact layer and is reflected by the n-electrode. This reflected light is extracted to the outside of the device. This structure exhibits high external quantum efficiency.

The results shown in Figures 10, 12, 14, 15, 17(a), 17(b), and 18 are essentially the same even if the Al composition of the graded Al composition intermediate layer in the simulation model shown in Figures 9(a) and 9(b) changes stepwise rather than linearly, as long as the discontinuity in the Al composition within the intermediate layer is sufficiently small.

Example 2
Measurement results relating to the contact structure will now be described. Fig. 19 is a diagram showing a device structure for an experiment relating to the contact structure.

19(a) and 19(b) show the epitaxial structure of the contact structure and the contact structure for electrical measurement. The epitaxial structure is fabricated by the following procedure. By MOVPE, the n-type AlGaN underlayer, the graded Al composition intermediate layer (n-type AlGaN), and the n-GaN contact layer are grown in sequence on the AlN template (not shown). The Al composition of the n-type AlGaN underlayer is 75%, and the film thickness is 500 nm. The starting Al composition of the graded Al composition intermediate layer is 75% (fixed), and the termination Al composition is 0%, 20%, and 40% to fabricate three types of epitaxial structures. In addition, the film thickness of the graded Al composition intermediate layer is 20 nm and 50 nm to fabricate two types of epitaxial structures. In both epitaxial structures, the film thickness of the contact layer is 200 nm. The epitaxial structure for reference does not include a graded Al composition intermediate layer, but includes an n-GaN contact layer grown directly on the underlying n-type AlGaN, as shown in FIG. 19(b).

As shown in Figures 19(a) and 19(b), electrodes are formed on the surface of the epitaxial structure by vacuum deposition. Metal films for electrodes of Ti/Al/Ni/Au (thickness: 30/100/70/150 nm) are deposited on the epitaxial structure. After depositing these metal films, a heat treatment is performed at 800 degrees Celsius for 2 minutes in a _N2 atmosphere.

To evaluate the contact resistance between the electrode and the contact layer, the electrodes include a circular electrode (inner electrode) and an annular electrode (outer electrode) surrounding it. The inner electrode and the outer electrode are formed so that the distance between them is several values in the range of 2 to 48 μm. Electrical measurements were performed using the circular transfer length method (cTLM).

19(c) and 19(d) show the contact structure for electrical measurement. In the electrode epitaxial structure having an inner electrode and an outer electrode, a groove is formed in the area between the inner electrode and the outer electrode by dry etching to reach the underlying n-type AlGaN.

20(a) and 20(b) show the results of electrical measurements of the contact structure shown in FIG. 19(b). FIG. 20(a) shows the current-voltage (IV) characteristics between two terminals, the inner electrode and the outer electrode, of the contact structure shown in FIG. 19(b). Since the IV curve is close to a straight line, it can be seen that the electrodes and the contact layer form good ohmic contact. FIG. 20(b) is a graph in which the resistance value between the two terminals obtained from FIG. 20(a) is plotted against the electrode spacing. The black dots (Experiment) in the graph show the measured values, and the dashed line (Fitting) shows the fitting curve obtained by least squares approximation from the experimental values using the following formula (1).
Formula (1): R=Rsh/2π{ln(r1/r2)+Lt(1/r1+1/r2)}
R: resistance value between two terminals r1: radius of inner electrode r2: radius of outer electrode Rsh: sheet resistance of semiconductor layer Lt: transmission length ln: natural logarithm Rsh and Lt are fitting parameters.
The characteristic contact resistance ρc between the electrode and the contact layer is calculated by the following formula (2).
Formula (2): ρc=Rsh×Lt ²
The characteristic contact resistance ρc derived by fitting is ρc=2.2×10 ⁻⁴ Ω·cm ² , and this experiment shows that the contact resistance between the electrode and the contact layer is low.

21(a) and 21(b) show the results of electrical measurements of the contact structure shown in FIG. 19(d). FIG. 21(a) shows the IV characteristic between two terminals, the inner electrode and the outer electrode, of the contact structure shown in FIG. 19(d). FIG. 21(b) is a graph in which the resistance between the two terminals obtained from FIG. 21(a) is plotted against the electrode spacing. The IV characteristic in FIG. 21(a) shows rectification. Comparing this with the linear IV characteristic shown in FIG. 20(a), it is presumed that this rectification characteristic occurs at the interface between the contact layer and the underlying n-type AlGaN. The dashed line shown in FIG. 21(b) was calculated using formula (1). The resistance value (vertical axis) shown in FIG. 21(b) is the resistance value at a current between the two terminals of 10 mA. The contact resistance derived from this graph using formula (2) is ρc=6.9×10 ⁻² Ω·cm ² . This characteristic contact resistance ρc is presumed to be the sum of the contact resistance at the electrode-contact layer interface, the resistance of the contact layer, and the contact resistance at the contact layer-underlying n-type AlGaN interface.

As already explained, the contact resistance at the electrode-contact layer interface is small. The resistance of the contact layer is also small. Therefore, the magnitude of the characteristic contact resistance ρc indicates that the contact resistance at the contact layer-underlying n-type AlGaN interface is large. A large contact resistance at the contact layer-underlying n-type AlGaN interface means that the voltage rise at the contact layer-underlying n-type AlGaN interface is large.

22(a) and 22(b) show the results of electrical measurements of the contact structure shown in FIG. 19(a). In this contact structure, the film thickness of the graded Al composition intermediate layer is 50 nm, and the terminal Al composition is 0%. FIG. 22(a) shows the IV characteristic between two terminals, the inner electrode and the outer electrode, of the contact structure shown in FIG. 19(a). Since the IV curve is linear, the IV characteristic in FIG. 22(a) shows good ohmic contact. FIG. 21(b) shows the resistance between the two terminals obtained from FIG. 22(a) plotted against the electrode spacing. The dashed line is derived by fitting. The characteristic contact resistance ρc by fitting is ρc=2.6×10 ⁻⁴ Ω·cm ² , which indicates that the contact resistance between the electrode and the contact layer is low.

23(a) and 23(b) show the results of electrical measurements of the contact structure shown in FIG. 19(c). In this contact structure, the thickness of the graded Al composition intermediate layer is 50 nm, and the termination Al composition is 0%. FIG. 23(a) shows the IV characteristic between two terminals, the inner electrode and the outer electrode, of the contact structure shown in FIG. 19(c). Since the IV curve is linear, the IV characteristic in FIG. 23(a) does not show rectification. FIG. 23(b) shows a graph in which the resistance between the two terminals obtained from FIG. 23(a) is plotted against the electrode spacing. The dashed line is derived by fitting. The characteristic contact resistance ρc by fitting is ρc=2.9×10 ⁻⁴ Ω·cm ² . This characteristic contact resistance ρc is presumed to be the sum of the contact resistance at the electrode-contact layer interface, the resistance of the contact layer, the contact resistance at the interface between the contact layer and the intermediate layer with graded Al composition, the resistance of the intermediate layer with graded Al composition, and the contact resistance at the interface between the intermediate layer with graded Al composition and the underlying n-type AlGaN. The contact resistance at the electrode-contact layer interface shown in FIG. 22(b) and the sum of the contact resistance at the electrode-contact layer interface shown in FIG. 23(b) and the contact resistance at each layer and each interface of the contact layer-underlying n-type AlGaN are very close, so the contact resistance at each layer and each interface of the contact layer-underlying n-type AlGaN is small. In other words, when the intermediate layer with graded Al composition is introduced, the voltage rise that occurs when a current flows from the contact layer to the underlying n-type AlGaN is very small.

Figure 24 is a graph showing the dependence of the characteristic contact resistance on the Al composition of the intermediate layer with graded Al composition for several film thicknesses. The vertical axis shows the characteristic contact resistance, and the horizontal axis shows the Al composition of the intermediate layer with graded Al composition. The characteristic contact resistance refers to the sum of the contact resistance of the electrode-contact layer interface and the contact layer-underlying n-type AlGaN layers and interfaces. Since all contact structures having the characteristics shown in the graph have substantially the same contact resistance of the electrode-contact layer interface, the resistance of the contact layer, and the resistance of the graded Al composition intermediate layer, the difference in the characteristic contact resistance in the graph is considered to reflect the difference in the sum of the contact resistance of the contact layer-graded Al composition intermediate layer interface and the contact resistance of the graded Al composition intermediate layer-underlying n-type AlGaN interface. The small contact resistance of these interfaces means that the voltage rise that occurs when current flows from the contact layer to the underlying n-type AlGaN is small.

The results in FIG. 24 show the following. First, a thicker film thickness (50 nm) of the intermediate layer with graded Al composition can contribute to reducing the characteristic contact resistance more than a thin film thickness (20 nm) of the intermediate layer with graded Al composition. Next, when the film thickness is thin (20 nm), the characteristic contact resistance becomes more dependent on the Al composition, and reaches a minimum value when the terminal Al composition of the intermediate layer with graded Al composition is 20%. Also, when the film thickness is thick (50 nm), the characteristic contact resistance becomes less dependent on the Al composition, and reaches a minimum value when the terminal Al composition of the intermediate layer with graded Al composition is 20%. These trends are similar to the results derived by simulation in the structure shown in FIG. 10(a) in which the intermediate layer with graded Al composition grows coherently with the underlying n-type AlGaN.

The experiment in Example 2 supports the results of the simulation in Example 1.

Example 3
FIG. 25 is a diagram showing the measurement results of X-ray diffraction reciprocal space mapping (XRD-RSM) of the epitaxial structure (not including electrodes) shown in FIG. 19(a). The epitaxial structure includes a starting Al composition of 75%, a terminal Al composition of 20%, and an intermediate layer of graded Al composition with a thickness of 50 nm. The XRD-RSM measurement was performed with (10-15) diffraction. From this mapping measurement, the lattice constants in the in-plane direction and the lattice constants perpendicular to the in-plane direction of each semiconductor layer in the epitaxial structure are derived. The peaks qc and qm corresponding to each semiconductor layer correspond to the reciprocal of the lattice constant in the c-axis direction and the reciprocal of the lattice constant in the m-axis direction, respectively. For example, the AlN and AlGaN buffer layers are omitted in FIG. 19(a), and the underlying n-type AlGaN is grown on these as the underlying in the epitaxial structure. The peak qc values of the AlN and AlGaN buffer layer are larger than the peak qc value of the underlying n-type AlGaN, so the lattice constants in the c-axis direction of the AlN homo-epilayer and the AlGaN buffer layer are smaller than the lattice constant in the c-axis direction of the underlying n-type AlGaN. On the other hand, the AlN, AlGaN buffer layer, and underlying n-AlGaN all have approximately equal peak qm values, so the lattice constants in the in-plane directions of these layers are approximately equal. This indicates that the AlN, AlGaN buffer layer, and underlying n-type AlGaN are growing coherently.

In FIG. 25, the qm of the peak corresponding to the intermediate layer with graded Al composition remains almost constant and is almost the same as the qm of the peak corresponding to the underlying n-type AlGaN. This indicates that the intermediate layer with graded Al composition grows coherently with the underlying n-type AlGaN. On the other hand, the peak corresponding to the intermediate layer with graded Al composition is shown as a measurement value that spreads in the qc direction at the same position as the peak qm value of the underlying n-type AlGaN. This reflects the continuous change in the lattice constant in the c-axis direction as the Al composition of the intermediate layer with graded Al composition changes continuously from 75% to 20%.

The absolute value of qm of the peak corresponding to the contact layer (n-GaN) is smaller than the absolute values of qm of AlN, the AlGaN buffer layer, the underlying n-type AlGaN, and the intermediate layer with graded Al composition. This indicates that the in-plane lattice constant of the contact layer (n-GaN) is larger than the in-plane lattice constants of the other semiconductor layers, and the contact layer (n-GaN) is lattice relaxed. In Figure 25, the lattice relaxation rate is estimated to be approximately 80%.

Example 4
26(a) to 26(f) are drawings showing differential interference microscope images of the surface of the epitaxial structure shown in FIG. 19(a). Specifically, FIGS. 26(a) to 26(c) show the surface morphology of a contact structure having a 20 nm thick graded Al composition intermediate layer, and FIGS. 26(d) to 26(f) show the surface morphology of a contact structure having a 50 nm thick graded Al composition intermediate layer. FIGS. 26(a) and 26(d) show the surface morphology of a contact structure having a graded Al composition intermediate layer with starting and ending Al compositions of 75% and 0%, respectively. FIGS. 26(b) and 26(e) show the surface morphology of a contact structure having a graded Al composition intermediate layer with starting and ending Al compositions of 75% and 20%, respectively. 26(c) and 26(f) show the surface morphology of the contact structure with a graded Al composition intermediate layer with starting and ending Al compositions of 75% and 40%, respectively.

The surface morphologies of Figures 26(b), 26(c), 26(e) and 26(f) are flatter than those of Figures 26(a) and 26(d). This suggests that lattice relaxation of the graded Al composition intermediate layer is suppressed in the growth of AlGaN with an Al composition of 20% or more. Good surface flatness of the contact layer is favorable for electrode formation thereon and other processes. For this reason, it is desirable for the terminal Al composition value of the graded Al composition intermediate layer to be 20% or more, which can provide good surface flatness.

FIG. 27 is a drawing showing the IV characteristics of a deep ultraviolet light emitting diode. The dashed line "Reference" shows the characteristics of the structure shown in FIG. 8(a), and the solid line "Novel" shows the characteristics of the structure shown in FIG. 9(a), that is, the structure of FIG. 8(a) in which a selectively grown stack including an n-type AlGaN intermediate layer with graded Al composition and an n-type GaN contact layer is provided between the n-electrode and the underlying n-type AlGaN. The starting Al composition of the n-type AlGaN intermediate layer with graded Al composition is 75%, and the ending Al composition is 20%. The thickness of the graded Al composition n-type AlGaN intermediate layer is 50 nm. The Al composition of the underlying n-type AlGaN is 75%. The contact structure using the contact layer and the intermediate layer with graded Al composition has a low resistance from the n-electrode to the underlying n-type AlGaN. Comparing the "Reference" with the "Novel", the operating voltage is reduced by about 4 V at 100 A/cm ² .

Example 5
The technical background of the contact structure will be described below. The Al composition of the n-type AlGaN base for a deep ultraviolet light emitting diode requires the following technical items.

First, deep ultraviolet light from the active layer can be transmitted through the underlying n-type AlGaN.
Specifically, if the emission wavelength is 285 nm, the underlying n-type AlGaN is required to have an Al composition of 40% or more, if the emission wavelength is 265 nm, the underlying n-type AlGaN is required to have an Al composition of 60% or more, and if the emission wavelength is 220 nm, the underlying n-type AlGaN is required to have an Al composition of 90% or more.

Second, the underlying n-type AlGaN must be grown coherently with respect to the underlying semiconductor.
When the underlying n-type AlGaN undergoes lattice relaxation and misfit dislocations occur, the crystal quality of the active layer is degraded, and the light emission efficiency is reduced. In order to suppress the lattice relaxation of the underlying n-type AlGaN, the underlying n-type AlGaN is grown coherently on the underlying AlN template or AlN substrate. For this purpose, typically, the Al composition of the underlying n-type AlGaN is desirably 50% or more, and more desirably 60% or more. From the viewpoint of coherent growth on AlN, it is preferable that the underlying n-type AlGaN has a larger Al composition. When the AlN template contains compressive strain, the range of the Al composition of the underlying n-type AlGaN that can be coherently grown on the AlN template is limited to a narrower range, i.e., a higher Al composition, than when the AlN template contains no strain or tensile strain.

Thirdly, electrons can be caused to drift in the in-plane direction in the underlying n-type AlGaN and spread out.
The n-type AlGaN underlayer is required to have high electrical conductivity in order to spread electrons from the electrode over the entire surface. If the Al composition of the n-type AlGaN underlayer exceeds 80%, its electrical conductivity drops sharply. It is desirable for the Al composition of the n-type AlGaN underlayer to be 80% or less. From the viewpoint of spreading electrons over the entire surface, it is preferable for the Al composition of the n-type AlGaN underlayer to be low.

Fourth, the junction between the n-type AlGaN underlayer and the n-electrode has a low contact resistance that exhibits ohmic properties.
When the contact between the n-type AlGaN underlayer and the n-electrode exhibits high contact resistance or exhibits Schottky characteristics, the voltage drop at this contact increases, causing a decrease in wall plug efficiency and an increase in heat generation. If the Al composition of the n-type AlGaN underlayer is high, the contact resistance increases and it becomes difficult to form an ohmic contact. For this reason, the Al composition of the n-type AlGaN underlayer is desirably 60% or less. From the viewpoint of good contact characteristics, it is better for the n-type AlGaN underlayer to have a low Al composition.

The Al composition of the n-type AlGaN substrate that satisfies the second and fourth items above is limited to a very narrow range. Therefore, it is difficult to form an n-type AlGaN substrate that can achieve low contact resistance with the n-electrode while suppressing the decrease in luminous efficiency that accompanies a decrease in the crystal quality of the active layer. In addition, in devices with short emission wavelengths, the first item imposes stricter requirements on the Al composition of the n-type AlGaN substrate than the second item. In this case, the first item becomes related to the contact characteristics.

The deep ultraviolet light emitting diode shown in FIG. 27 includes a template layer 120 made of AlN and an n-type semiconductor layer 125 made of AlGaN. The (0002) rocking curve full width at half maximum (XRC-FWHM) of the template layer 120 made of AlN evaluated by X-ray diffraction measurement is 29 arcsec, and the (10-12) XRC-FWHM is 262 arcsec. The (0002) XRC-FWHM of the n-type semiconductor layer 125 made of AlGaN is 49 arcsec, and the (10-12) XRC-FWHM is 251 arcsec.

A typical example of this embodiment is shown below.

A first embodiment of the present invention is a semiconductor light-emitting device comprising: an n-type semiconductor layer including a group III nitride semiconductor containing aluminum as a group III constituent element; a p-type semiconductor layer provided on the n-type semiconductor layer; an active layer including a group III nitride semiconductor and capable of generating deep ultraviolet light provided on the n-type semiconductor layer; an n-type contact layer of a group III nitride semiconductor containing gallium as a group III constituent element provided on the n-type semiconductor layer; an n-type intermediate region of a group III nitride semiconductor containing gallium and aluminum as group III constituent elements provided on the n-type semiconductor layer; and an n-electrode containing a metal, the n-type intermediate region being provided between the n-type contact layer and the n-type semiconductor layer, and the n-type contact layer being disposed between the n-type intermediate region and the p-type semiconductor layer. and the n-electrode, the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the n-type contact layer, the Al composition Y of the n-type contact layer is equal to or greater than zero, the Al composition X of the n-type intermediate region is equal to or less than the Al composition Z of the n-type semiconductor layer, the Al composition X of the n-type intermediate region changes monotonically in the direction from the n-type semiconductor layer to the n-type contact layer, the n-type intermediate region has at least one of a graded composition and a step composition in which the Al composition X of the n-type intermediate region decreases in the direction from the n-type semiconductor layer to the n-type contact layer in at least a portion of the n-type intermediate region, and the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are arranged in order in the direction of the axis from the n-type intermediate region to the n-electrode.

In the semiconductor light-emitting device, the n-type intermediate region having an Al composition X that changes monotonically in the direction from the n-type semiconductor layer to the n-type contact layer provides good electrical characteristics to the contact structure for providing carriers to the active layer via the n-type semiconductor layer.

The Al composition Y of the n-type contact layer is equal to or less than the Al composition X of any area of the n-type intermediate region. The Al composition Z of the n-type semiconductor layer is equal to or greater than the Al composition X of any area of the n-type intermediate region.

In the semiconductor light-emitting device according to the first embodiment, the n-type intermediate region has at least one of a graded composition and a step composition in which the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer in at least a portion of the n-type intermediate region.

In semiconductor light-emitting devices, the monotonically changing Al composition in the n-type intermediate region is provided by a graded composition and a step composition.

In the semiconductor light emitting device according to the first aspect, the n-type intermediate region comprises Al _x Ga _1-xN , and the Al composition X of the n-type intermediate region decreases throughout the n-type intermediate region in a direction from the n-type semiconductor layer to the n-type contact layer.

In the semiconductor light-emitting device, the n-type intermediate region has an interface associated with the n-type semiconductor layer and an interface associated with the n-type contact layer, and the Al composition X decreases from one interface to the other interface.

In the semiconductor light-emitting device according to the first embodiment, the n-type contact layer includes one of n-type GaN, n-type AlGaN, or n-type InAlGaN.

In the semiconductor light-emitting device, the n-type contact layer can be provided with a gallium nitride-based semiconductor such as n-type GaN, n-type AlGaN, or n-type InAlGaN.

In the semiconductor light-emitting device according to the first embodiment, the in-plane lattice constant of the n-type contact layer is equal to or greater than the in-plane lattice constant of the n-type intermediate region.

In the semiconductor light-emitting device, the n-type contact layer is provided with a group III nitride that is lattice-relaxed relative to the n-type intermediate region. The n-type contact layer that is lattice-relaxed relative to the n-type intermediate region can reduce the electrical resistance at the interface between the n-type contact layer and the n-type intermediate region.

In the semiconductor light-emitting device according to the first embodiment, the n-type contact layer has a lattice relaxation rate of 0.5 or more relative to the n-type semiconductor layer.

In the semiconductor light-emitting device, the n-type contact layer can be provided with a Group III nitride having a lattice relaxation rate of 0.5 or more relative to the n-type semiconductor layer.

In the semiconductor light-emitting device according to the first embodiment, the Group III nitride semiconductor of the n-type semiconductor layer includes either AlN or AlGaN.

In a semiconductor light-emitting device, AlN or AlGaN can be used as the base for the n-type contact layer and the n-type intermediate region.

In the semiconductor light-emitting device according to the first embodiment, the wavelength of the deep ultraviolet light is in the range of 285 nm or less.

In semiconductor light-emitting devices, deep ultraviolet light with a wavelength of 285 nm or less requires an active layer with a high Al composition, and the current path to the active layer is also formed by a group III nitride with a high Al composition. A good n-side contact structure to the group III nitride with a high Al composition is provided by a combination of an n-type intermediate region, an n-type contact layer, and an n-electrode.

The semiconductor light-emitting device according to the first embodiment further comprises a substrate providing a Group III nitride primary surface containing aluminum as a Group III constituent element, the substrate being equipped with the n-type semiconductor layer, the active layer, the p-type semiconductor layer, the n-type contact layer, and the n-type intermediate region, the substrate being a substrate containing Group III nitride containing aluminum as a Group III constituent element, or a substrate including a support made of a material different from Group III nitride, and an AlN template layer or an AlGaN template layer provided on the primary surface of the support.

In a semiconductor light-emitting device, an active layer is provided on a substrate such as the one described above.

In the semiconductor light-emitting device according to the first embodiment, the difference between the Al composition Y of the n-type contact layer and the Al composition X of the n-type intermediate region can be 0.3 or less at the interface between the n-type contact layer and the n-type intermediate region, and the difference between the Al composition X of the n-type intermediate region and the Al composition Z of the n-type semiconductor layer can be 0.3 or less at the interface between the n-type intermediate region and the n-type semiconductor layer.

In a semiconductor light-emitting device, the above-mentioned Al composition difference can provide the semiconductor light-emitting device with good electrical characteristics.

A second aspect of the embodiment is a method for producing a semiconductor light-emitting device, the semiconductor light-emitting device including an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, the active layer including a Group III nitride semiconductor capable of generating deep ultraviolet light, the method including: growing a first Group III nitride semiconductor layer for an n-type intermediate region including gallium and aluminum as Group III constituent elements on a substrate; growing a second Group III nitride semiconductor layer for an n-type contact layer including gallium as a Group III constituent element on the substrate after growing the first Group III nitride semiconductor layer; and forming an n-electrode including a metal on the substrate after growing the second Group III nitride semiconductor layer, the n-type semiconductor layer including aluminum as a Group III constituent element, the n-type intermediate region including a metal between the n-type contact layer and the n-type semiconductor layer. The n-type contact layer is provided between the n-type intermediate region and the n-electrode, the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the n-type contact layer, the Al composition Y of the n-type contact layer is equal to or greater than zero, the Al composition X of the n-type intermediate region is equal to or less than the Al composition Z of the n-type semiconductor layer, the Al composition X of the n-type intermediate region changes monotonically in the direction from the n-type semiconductor layer to the n-type contact layer, the n-type intermediate region has at least one of a graded composition and a step composition in which the Al composition X of the n-type intermediate region decreases in at least a portion of the n-type intermediate region in the direction from the n-type semiconductor layer to the n-type contact layer, and the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are sequentially arranged on the substrate in the direction of the axis from the n-type intermediate region to the n-electrode.

According to this manufacturing method, the n-type intermediate region having an Al composition X that changes monotonically in the direction from the n-type semiconductor layer to the n-type contact layer provides good electrical characteristics to the contact structure for providing carriers to the active layer via the n-type semiconductor layer. The Al composition Y of the n-type contact layer is equal to or less than the Al composition X of any area of the n-type intermediate region. The Al composition Z of the n-type semiconductor layer is equal to or greater than the Al composition X of any area of the n-type intermediate region.

In a method of fabricating a semiconductor light emitting device according to a second aspect, the n-type intermediate region comprises Al _x Ga _1-x N, and the Al composition X of the n-type intermediate region decreases throughout the n-type intermediate region in a direction from the n-type semiconductor layer to the n-type contact layer.

According to this manufacturing method, the n-type intermediate region has an interface associated with the n-type semiconductor layer and an interface associated with the n-type contact layer, and the Al composition X decreases from one of these interfaces toward the other.

In the method for producing a semiconductor light-emitting device according to the second embodiment, the in-plane lattice constant of the n-type contact layer is equal to or greater than the in-plane lattice constant of the n-type intermediate region.

This fabrication method allows the n-type contact layer to be provided with a group III nitride that is lattice-relaxed relative to the n-type intermediate region.

In the method for producing a semiconductor light-emitting device according to the second embodiment, the n-type contact layer has a lattice relaxation rate of 0.5 or more relative to the n-type semiconductor layer.

According to this manufacturing method, the n-type contact layer can be provided with a group III nitride having a lattice relaxation rate of 0.5 or more relative to the n-type semiconductor layer.

In the method for producing a semiconductor light-emitting device according to the second embodiment, the n-type contact layer includes one of n-type GaN, n-type AlGaN, or n-type InAlGaN.

According to this manufacturing method, the n-type contact layer can be provided with gallium nitride semiconductors such as n-type GaN, n-type AlGaN, or n-type InAlGaN.

In the method for producing a semiconductor light-emitting device according to the second embodiment, the n-type intermediate region has a graded composition and a step structure in which the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer in at least a portion of the n-type intermediate region.

According to the manufacturing method, the monotonically changing Al composition in the n-type intermediate region is provided by a graded composition and a step structure.

In the method for producing a semiconductor light-emitting device according to the second embodiment, the wavelength of the deep ultraviolet light is in the range of 285 nm or less.

According to the manufacturing method, for deep ultraviolet light with a wavelength of 285 nm or less, an active layer with a high Al composition is required, and the current path to the active layer is also formed by a group III nitride with a high Al composition. A good n-side contact structure to the group III nitride with a high Al composition is provided by the combination of an n-type intermediate region, an n-type contact layer, and an n-electrode.

In the method for producing a semiconductor light-emitting device according to the second embodiment, the substrate provides a Group III nitride primary surface containing aluminum as a Group III constituent element, and the substrate is equipped with the n-type semiconductor layer, the active layer, the p-type semiconductor layer, the n-type contact layer, and the n-type intermediate region, and the substrate is a substrate containing Group III nitride containing aluminum as a Group III constituent element, or a substrate including a support made of a material different from Group III nitride, and an AlN template layer or an AlGaN template layer provided on the primary surface of the support.

According to the manufacturing method, an active layer is provided on the substrate as described above.

A third aspect of the embodiment is a contact structure for a Group III nitride semiconductor device, comprising: a substrate providing a Group III nitride primary surface containing aluminum as a Group III constituent element; a semiconductor region in contact with the Group III nitride primary surface and containing one or more Group III nitride semiconductor layers; an n-type semiconductor layer of Group III nitride semiconductor in contact with the semiconductor region; an n-type contact layer of Group III nitride semiconductor provided on the n-type semiconductor layer and containing gallium as a Group III constituent element; an n-type intermediate region of Group III nitride semiconductor provided on the n-type semiconductor layer and containing gallium and aluminum as Group III constituent elements; and an n-electrode containing a metal, wherein the Group III nitride semiconductor of the n-type semiconductor layer contains aluminum as a Group III constituent element, and the n-type semiconductor The layer is provided between the substrate and the n-type intermediate region, the n-type intermediate region is provided between the n-type contact layer and the n-type semiconductor layer, the n-type contact layer is provided between the n-type intermediate region and the n-electrode, the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the n-type contact layer, the Al composition Y of the n-type contact layer is equal to or greater than zero, the Al composition X of the n-type intermediate region is equal to or less than the Al composition Z of the n-type semiconductor layer, the Al composition X of the n-type intermediate region changes monotonically in the direction from the n-type semiconductor layer to the n-type contact layer, and the n-type intermediate region has at least one of a graded composition and a step composition in which the Al composition X of the n-type intermediate region decreases in at least a portion of the n-type intermediate region in the direction from the n-type semiconductor layer to the n-type contact layer.

According to the contact structure, the n-type intermediate region having an Al composition X that changes monotonically in the direction from the n-type semiconductor layer to the n-electrode provides the contact structure with good electrical characteristics for providing carriers to the n-type semiconductor layer. In the contact structure, the n-type intermediate region, the n-type contact layer, and the n-electrode are arranged in this order. The Al composition Y of the n-type contact layer is equal to or less than the Al composition X of any area of the n-type intermediate region. Also, the Al composition Z of the n-type semiconductor layer is equal to or greater than the Al composition X of any area of the n-type intermediate region.

The contact structure according to the third embodiment further comprises a p-type semiconductor layer provided on the substrate, and an active layer including a Group III nitride semiconductor provided on the substrate and capable of generating deep ultraviolet light, and the substrate, the n-type semiconductor layer, the active layer, and the p-type semiconductor layer are sequentially arranged in the direction of an axis extending from the n-type contact layer to the n-electrode.

The contact structure provides good electrical characteristics to a semiconductor device having an n-type semiconductor layer closer to the substrate than the p-type semiconductor layer. In the contact structure, the n-type intermediate region, the n-type contact layer, and the n-electrode are arranged in that order.

In the contact structure according to the third embodiment, the n-type semiconductor layer has at least one of a graded composition that changes monotonically in the direction from the substrate to the n-type contact layer and a step structure.

According to the contact structure, the n-type semiconductor layer can have a monotonically varying Al composition, and the monotonically varying Al composition is provided by a graded composition and step structure having an Al composition less than or equal to the maximum value of the Al composition X.

In the contact structure according to the third embodiment, the n-type semiconductor layer has a single Al composition.

According to the contact structure, the n-type semiconductor layer can have a single Al composition. The technical meaning of "single Al composition" is determined taking into account the measurement variability of the Al composition.

The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. All such modifications are included in the technical concept of the present invention.

110: nitride device, 111: contact structure, 113: lower III-nitride stack, 114: active layer, 114a: quantum well structure, 114b: well layer, 114c: barrier layer, 115: upper III-nitride stack, 116: nitride semiconductor region, 118: support, 118a: primary surface, 119a, 119b, 119c, 119d: junction, 120: template layer, 121: p-type semiconductor layer, 122: first n-type semiconductor layer, 124: second n-type semiconductor layer, 125: n-type semiconductor layer, 125a: first region, 125b: second region, 127: n-type contact layer, 129: n-type intermediate region, 130: Al _U Ga _1-U N layer, 131: n-electrode, 132: Al _V Ga _1-V N layer, 133...substrate, 133a...III-nitride main surface, 134...electron block layer, 135...semiconductor region, 135a...main surface, 136...p-type gradient composition layer, 138, 138a, 138b...p-type contact layer, 142...etched region, 144...passivation film, 144a, 144b...opening, 146...p-electrode, 150...substrate, 155a, 155b...MOVPE reactor, 162...epitaxial wafer, 163...group III nitride semiconductor layer, 164...group III nitride stack, 165...first n-type semiconductor layer, 166...nitride semiconductor region, 167...second n-type semiconductor layer, 168...active layer, 168a...quantum well structure, 168b...well layer, 168c...barrier layer, 169...n-type intermediate region, 170...Al _U Ga _1-U N layer, 171 . . . n-type contact layer, 172 . . . Al _V Ga _1-V N layer, 173 . . . hard mask, 173a . . . opening, 174 . . . electron blocking layer, 175 . . . contact stack, 176 . . . p-type graded composition layer, 178 . . . p-type contact layer, 180a, 180b . . . groove, 182 . . . processed region by etching, 184 . . . passivation film, 184a, 184b . . . opening, 186 . . . p-electrode, 188 . . . n-electrode, ρc . . . characteristic contact resistance.

Claims (12)

1. A semiconductor light emitting device, comprising:
an n-type semiconductor layer including a Group III nitride semiconductor containing aluminum as a Group III constituent element;
a p-type semiconductor layer provided on the n-type semiconductor layer;
an active layer including a group III nitride semiconductor provided on the n-type semiconductor layer and capable of generating deep ultraviolet light;
an n-type contact layer made of a Group III nitride semiconductor containing gallium as a Group III constituent element provided on the n-type semiconductor layer;
an n-type intermediate region of a Group III nitride semiconductor including gallium and aluminum as Group III constituent elements provided on the n-type semiconductor layer;
an n-electrode comprising a metal;
Equipped with
the n-type intermediate region is provided between the n-type contact layer and the n-type semiconductor layer,
the n-type contact layer is provided between the n-type intermediate region and the n-electrode,
the n-type contact layer has an in-plane lattice constant equal to or larger than the in-plane lattice constant of the n-type intermediate region;
the n-type contact layer has a lattice relaxation rate of 0.5 or more with respect to the n-type semiconductor layer,
the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the n-type contact layer, and the Al composition Y of the n-type contact layer is equal to or greater than zero;
the Al composition X of the n-type intermediate region is equal to or smaller than the Al composition Z of the n-type semiconductor layer;
the Al composition X of the n-type intermediate region changes monotonically in a direction from the n-type semiconductor layer to the n-type contact layer,
the n-type intermediate region has at least one of a graded composition and a step composition in which the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer in at least a portion of the n-type intermediate region,
The n-type semiconductor layer, the active layer, and the p-type semiconductor layer are sequentially arranged in the direction of an axis from the n-type intermediate region toward the n-electrode.
Semiconductor light emitting device. the n-type intermediate region comprises Al _x Ga _1-x N;
the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer throughout the n-type intermediate region;
10. The semiconductor light emitting device of claim 1. The n-type contact layer includes any one of n-type GaN, n-type AlGaN, and n-type InAlGaN.
3. A semiconductor light emitting device according to claim 1 or 2. The wavelength of the deep ultraviolet light is in the range of 285 nm or less.
A semiconductor light emitting device according to any one of claims 1 to 3 . The semiconductor device further includes a substrate providing a Group III nitride primary surface including aluminum as a Group III constituent element,
the substrate includes the n-type semiconductor layer, the active layer, the p-type semiconductor layer, the n-type contact layer, and the n-type intermediate region;
The substrate is a substrate including a Group III nitride having aluminum as a Group III constituent element, or a substrate including a support made of a material other than Group III nitride, and an AlN template layer or an AlGaN template layer provided on a primary surface of the support.
A semiconductor light emitting device according to any one of claims 1 to 4 . a difference between the Al composition Y of the n-type contact layer and the Al composition X of the n-type intermediate region is 0.3 or less at an interface between the n-type contact layer and the n-type intermediate region,
a difference between the Al composition X of the n-type intermediate region and the Al composition Z of the n-type semiconductor layer is 0.3 or less at an interface between the n-type intermediate region and the n-type semiconductor layer;
A semiconductor light emitting device according to any one of claims 1 to 5 . 1. A method of fabricating a semiconductor light emitting device, the semiconductor light emitting device comprising an n-type semiconductor layer, an active layer, and a p-type semiconductor layer, the active layer comprising a Group III nitride semiconductor capable of generating deep ultraviolet light, the method comprising:
growing a first Group III nitride semiconductor layer for an n-type intermediate region on the substrate, the first Group III nitride semiconductor layer including gallium and aluminum as Group III constituent elements;
growing, on the substrate, a second Group III nitride semiconductor layer for an n-type contact layer, the second Group III nitride semiconductor layer containing gallium as a Group III constituent element, after growing the first Group III nitride semiconductor layer;
forming an n-electrode containing a metal on the substrate after growing the second Group III nitride semiconductor layer;
Equipped with
the n-type semiconductor layer contains aluminum as a group III constituent element,
the n-type intermediate region is provided between the n-type contact layer and the n-type semiconductor layer,
the n-type contact layer is provided between the n-type intermediate region and the n-electrode,
the n-type contact layer has an in-plane lattice constant equal to or larger than the in-plane lattice constant of the n-type intermediate region;
the n-type contact layer has a lattice relaxation rate of 0.5 or more with respect to the n-type semiconductor layer,
the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the n-type contact layer, and the Al composition Y of the n-type contact layer is equal to or greater than zero;
the Al composition X of the n-type intermediate region is equal to or smaller than the Al composition Z of the n-type semiconductor layer;
the Al composition X of the n-type intermediate region changes monotonically in a direction from the n-type semiconductor layer to the n-type contact layer,
the n-type intermediate region has at least one of a graded composition and a step composition in which the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer in at least a portion of the n-type intermediate region,
The n-type semiconductor layer, the active layer, and the p-type semiconductor layer are sequentially arranged on the substrate in the direction of an axis from the n-type intermediate region to the n-electrode.
A method for making a semiconductor light emitting device. the n-type intermediate region comprises Al _x Ga _1-x N;
the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer throughout the n-type intermediate region;
A method for making the semiconductor light emitting device of claim 7 . The n-type contact layer includes any one of n-type GaN, n-type AlGaN, and n-type InAlGaN;
A method for making a semiconductor light emitting device according to claim 7 or claim 8 . The wavelength of the deep ultraviolet light is in the range of 285 nm or less.
A method for making a semiconductor light emitting device according to any one of claims 7 to 9 . the substrate provides a Group III nitride primary surface containing aluminum as a Group III constituent element;
the substrate includes the n-type semiconductor layer, the active layer, the p-type semiconductor layer, the n-type contact layer, and the n-type intermediate region;
The substrate includes a substrate including a group III nitride including aluminum as a group III constituent element, or a substrate including a support body made of a material different from group III nitride, and an AlN template layer or an AlGaN template layer provided on a primary surface of the support body.
A method for making a semiconductor light emitting device according to any one of claims 7 to 10 . 1. A contact structure for a Group III nitride semiconductor device, comprising:
a substrate providing a Group III nitride primary surface containing aluminum as a Group III constituent element;
a semiconductor region in contact with the Group III nitride primary surface and including one or more Group III nitride semiconductor layers;
an n-type semiconductor layer of a Group III nitride semiconductor in contact with the semiconductor region;
an n-type contact layer made of a Group III nitride semiconductor containing gallium as a Group III constituent element provided on the n-type semiconductor layer;
an n-type intermediate region of a Group III nitride semiconductor including gallium and aluminum as Group III constituent elements provided on the n-type semiconductor layer;
an n-electrode comprising a metal;
Equipped with
the Group III nitride semiconductor of the n-type semiconductor layer contains aluminum as a Group III constituent element,
the n-type semiconductor layer is provided between the substrate and the n-type intermediate region,
the n-type intermediate region is provided between the n-type contact layer and the n-type semiconductor layer,
the n-type contact layer is provided between the n-type intermediate region and the n-electrode,
the n-type contact layer has an in-plane lattice constant equal to or larger than the in-plane lattice constant of the n-type intermediate region;
the n-type contact layer has a lattice relaxation rate of 0.5 or more with respect to the n-type semiconductor layer,
the Al composition X of the n-type intermediate region is equal to or greater than the Al composition Y of the n-type contact layer, and the Al composition Y of the n-type contact layer is equal to or greater than zero;
the Al composition X of the n-type intermediate region is equal to or smaller than the Al composition Z of the n-type semiconductor layer;
the Al composition X of the n-type intermediate region changes monotonically in a direction from the n-type semiconductor layer to the n-type contact layer,
the n-type intermediate region has at least one of a graded composition and a step composition in which the Al composition X of the n-type intermediate region decreases in a direction from the n-type semiconductor layer to the n-type contact layer in at least a portion of the n-type intermediate region;
Contact structure.