JP3767660B2 - Multilayer structure and compound semiconductor device using the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a laminated structure including a group III nitride semiconductor layer laminated on a crystal substrate via a buffer layer.
[0002]
[Prior art]
Aluminum nitride / gallium mixed crystal (Al_xGa_yN: 0 ≦ x, y ≦ 1, x + y = 1) or gallium nitride / indium mixed crystal (Ga_xIn_yGroup III nitride semiconductors such as N: 0 ≦ x, y ≦ 1, x + y = 1) are short wavelength visible light emitting diodes (English abbreviation: LED), laser diodes (abbreviation: LD), or photodiodes such as blue (Abbreviation: PD) and the like are used as layers constituting Group III nitride semiconductor optical devices (see Mat. Res. Soc. Symp. Proc., Vol. 449 (1997), pages 509 to 518). Further, it is used to construct a group III nitride semiconductor electronic device such as a Schottky junction field effect transistor (English abbreviation: MESFET) (Proc. OF THE TOPICAL WORKSHOP ON III-V NITRIDES (21 -23. Sept. 1995) (PERGAMON PRESS), see pages 97-100.
[0003]
Conventionally, these compound semiconductor devices have been exclusively sapphire (α-Al) belonging to the hexagonal system.₂O_Three(Single crystal) as a substrate. The a-axis lattice constant of sapphire is 4.785４. The lattice constant of the a-axis of hexagonal gallium nitride (chemical formula: GaN), which is the main constituent material of the conventional laminated structure, is 3.180Å (written by Akazaki Isao, “III-V Group Compound Semiconductor” (1994) May 20, first edition, published by Baifukan Co., Ltd., Table 7.1 on page 148) Therefore, the degree of mismatch between gallium nitride and sapphire as a substrate takes into account the orientation of GaN on sapphire. However, the size reaches 13.8% (see “The Journal of Japanese Society for Crystal Growth”, Vol. 15, No. 3 & 4 (1988), pages 75 to 82).
The degree of lattice mismatch between indium nitride (chemical formula: InN) having a lattice constant of 3.533Å, which is one constituent material of the conventional laminated structure, and hexagonal gallium nitride also reaches about 11.1%. As described above, the conventional laminated structure for use in group III nitride semiconductor devices has a structure of a lattice mismatch system including a mismatch of about 10%.
[0004]
When the degree of lattice mismatch between the constituent layers of the substrate material and the laminated structure is large, it is extremely difficult to stack a continuous and good crystalline epitaxial thin film layer. Therefore, in a conventional laminated structure for a group III nitride semiconductor device, for example, a buffer layer is disposed for the purpose of relaxing lattice mismatch between the hexagonal sapphire substrate and the laminated structure constituting layer. It has become a common practice.
[0005]
The buffer layer is usually Al_XGa_YN (0.ltoreq.X, Y.ltoreq.1) mixed crystal (refer to Japanese Patent Laid-Open Nos. 2-229476 and 4-297023). Since the buffer layer is practically formed at a relatively low temperature of about 400 ° C. to about 600 ° C., it is called a low temperature buffer layer. Conventionally, an important requirement to be provided as a buffer layer is a hexagonal wurzite type amorphous crystal layer in which microcrystals are mixed (Japanese Patent Laid-Open No. Hei 2-229476). Refer to the book). That is, in the conventional laminate, a buffer layer made of a hexagonal group III nitride semiconductor is usually included on the surface of a hexagonal crystal substrate.
[0006]
By the way, there are the following peculiar problems that the conventional laminated structure is composed of the crystal layer mainly composed of hexagonal crystals as described above.
[0007]
That is, a hexagonal gallium nitride based semiconductor originally exhibits a piezo effect (piezoelectric effect). In a MODFET that requires high-speed response of electrons and a large-capacity power device, charge separation due to the piezoelectric effect deters normal operation of electrons. Therefore, in order to configure a device having excellent high-speed response, it is advantageous to configure it from a laminated structure that does not include polarization due to the piezoelectric effect.
[0008]
The strength of the piezoelectric effect varies depending on the crystal system even for the same group III nitride semiconductor. In cubic III-nitride semiconductors, the piezoelectric effect is unlikely to occur (1996 Lead Research Report NEDO-PR-9605, "Hard Electronics" (March 1997) (See New Functional Device Research and Development Association), page 75). This is a potential factor that is advantageous for obtaining a device that exhibits high-speed response of electrons.
[0009]
Also, in the cubic crystal, the band narrowing on the valence band side is not released (co-authored by Toshiaki Ikoma and Hideaki Ikoma, “Introduction to Basic Properties of Compound Semiconductors” (first edition on September 10, 1991, Baifukan Co., Ltd.) (See page 17), forming a low-resistance p-type conductive layer is easier than hexagonal crystals (see JP-A-2-275682). The characteristic of cubic that the p-type conductive layer can be easily formed is that each laminated structure for power electronic device diodes such as LED, LD, or abbreviated IGBT (insulated gate bipolar transistor) including a pn junction. It is an excellent quality that is important in building a stable.
[0010]
For this reason, recently, an attempt has been made to construct a laminated structure for device use with a cubic group III nitride semiconductor crystal layer. The conventional technology intended to form a stacked structure for a device from a cubic group III nitride semiconductor crystal layer is based on a single crystal silicon (Si) or gallium arsenide (GaAs) as a substrate crystal. . This is because, in order to grow a hexagonal crystal predominantly on the hexagonal crystal, a diamond structure type Si and zinc blende belonging to the cubic system is used. This is because it is inherently advantageous to use a zinc blend type GaAs as a substrate crystal.
[0011]
However, it is known that a cubic crystal phase and a hexagonal crystal phase are mixed inside a group III nitride semiconductor layer directly formed on a cubic substrate crystal. For example, in the example of a GaN growth layer formed on a GaAs substrate, it has been reported that hexagonal crystals are mixed at about 10% (1997). Collection No. 1 (Japan Society for Applied Physics, published on October 2, 1997), lecture number 3p-Q-15, see page 316).
[0012]
In view of this background, even when a stacked structure is formed using a cubic Si single crystal as a substrate, an operation of depositing each constituent layer of the stacked structure through a buffer layer is performed. As a constituent material of the buffer layer in this case, silicon carbide (SiC) is used, and this silicon carbide includes hexagonal silicon carbide (referred to as 6H—SiC) and cubic silicon carbide (3C). (Referred to as "SiC and related wide gap semiconductor study group 5th lecture proceedings" (hosted by the Japan Society of Applied Physics, October 31 to November 1, 1996), page 20. And Proc. TOPICAL MEETING WORKSHOP ON III-V NITRIDES (Sept. 21-23, 1995), PERGAMON PRESS, pages 335-338). And since a hexagonal group III nitride semiconductor layer grows predominantly on hexagonal 6H—SiC, it is not suitable for forming a cubic group III nitride semiconductor crystal layer.
[0013]
On the other hand, if the buffer layer is composed of cubic 3C-SiC, it is expected that a cubic group III nitride semiconductor layer can be overlaid, but the hexagonal and cubic crystal phases are actually formed on the buffer layer. A crystal layer containing a mixture of nuclei is formed (Preliminary Proceedings of the 58th JSAP Autumn Meeting, 1997 (Heisei 9), Japan Society of Applied Physics, published on October 2, 1997) , Lecture number 3p-Q-19, pages 317)). Taking gallium nitride (GaN) as an example of a group III nitride semiconductor to be stacked, the band gap of hexagonal GaN at room temperature is 3.39 electron volts (eV), and that of cubic is 3.29 eV. is there. In addition, the lattice constant of the a axis is 3.18Å in the hexagonal crystal, whereas it is greatly different from 4.51Å in the cubic crystal. That is, mixing different crystal systems in the same growth layer means that the layer is a mixture of semiconductor materials having different band gaps and lattice constants. As a result, in a light-emitting device in which such a crystal system layer is used as a light-emitting layer, problems such as non-uniformity of the emission wavelength result. Not only in light emitting devices but also in other devices, the occurrence of inadvertent lattice distortion due to the difference in lattice constant at the hexagonal / cubic interface is an obstacle to the formation of a homogeneous semiconductor functional layer. It is obvious.
[0014]
Thus, when cubic 3C-SiC is used for the buffer layer, the upper layer stack is inhomogeneous in which hexagonal crystals and cubic crystals are mixed, and thus a growth layer having a uniform crystal form is obtained. Above, cubic 3C-SiC is not necessarily suitable for the buffer layer.
[0015]
There are also conventional examples using phosphorous boron (chemical formula: BP) as a buffer layer material on a Si substrate (Japanese Patent Laid-Open Nos. 2-275682, 2-88381 and 2-288388). Refer to the book). It is already known that a BP single crystal film can be formed on a Si crystal (Naoya Shibusawa, Kazutaka Terashima, 28th Annual Meeting of the Japanese Society for Crystal Growth, No. 28aB11 (Journal of Japanese Society for Crystal Growth, Vol. 24, No. 24). 2 (1997), page 150)). The advantage of using the BP layer is that the lattice constant of cubic BP (4.538 mm) (written by Akazaki Isao, “III-V group compound semiconductor” (May 20, 1994, first edition, published by Baifukan Co., Ltd.), 148 Table 7.1 on page) and the degree of mismatch between cubic gallium nitride (lattice constant = 4.510Å) are only 0.6%. Due to the small degree of lattice mismatch with respect to cubic gallium nitride, recently BP is a material constituting a side block layer surrounding an active (light emitting) layer for unifying the oscillation mode of laser light. (See Japanese Patent Laid-Open No. 9-232685).
[0016]
[Problems to be solved by the invention]
However, although BP and cubic GaN have good lattice matching, they do not have a perfect lattice matching relationship, and a slight lattice mismatch remains. Then, when stacking with this degree of lattice mismatch remaining, misfit dislocations caused by this lattice mismatch cause the crystal defect density in the stack constituting layer to be further expanded. As a result, various device characteristics are hindered. For this reason, it has been found that it is extremely important that the lattice matching with the buffer layer is almost perfect.
[0017]
The present invention has been proposed in view of the above, and provides a laminated structure having a buffer layer capable of almost perfecting the consistency with a cubic group III nitride semiconductor layer laminated on the upper surface thereof. For the purpose.
[0018]
[Means for Solving the Problems]
  In order to achieve the above object, according to a first aspect of the present invention, there is provided a stacked structure formed on a substrate, a cubic crystal substrate, and a boron gallium phosphide mixed crystal formed on the crystal substrate ( B_xGa_1-xA buffer layer composed of P: 0 ≦ x ≦ 1) and having a gradient in the composition of the Group III element, and a general structural formula mainly composed of cubic crystals formed on the buffer layer and having a general structural formula of GaN_qAs_1-qA group III nitride semiconductor layer represented by (0 <q <1),Above mismatch rate of 0.1% or less III The lattice constant of the group nitride semiconductor layer substantially matches the lattice constant of the surface composition of the buffer layer,It is characterized by that.
[0019]
  According to a second aspect of the present invention, there is provided a stacked structure formed on a substrate, a cubic crystal substrate, and a boron phosphide mixed crystal (BN) formed on the crystal substrate._zP_1-z: A buffer layer composed of 0 ≦ z ≦ 1) and having a gradient in the composition of the group V element, and a general structural formula mainly composed of cubic crystals formed on the buffer layer and having a general structural formula of GaN_qAs_1-qA group III nitride semiconductor layer represented by (0 <q <1),Above mismatch rate of 0.1% or less III The lattice constant of the group nitride semiconductor layer substantially matches the lattice constant of the surface composition of the buffer layer,It is characterized by that.
[0020]
  The invention according to claim 3 is the above-described claim.2In addition to the configuration of the invention described in (2), the buffer layer is formed by stacking layers having different composition ratios of the group V elements constituting the buffer layer.By adding a gradient to the compositionIt is characterized by.
[0021]
  According to a fourth aspect of the present invention, there is provided a stacked structure formed on a substrate, a cubic crystal substrate, and a boron gallium phosphide mixed crystal (B) on the crystal substrate._xGa_1-xP: 0 ≦ x ≦ 1)First III Gradient composition of group elementsA first buffer layer and a boron phosphide boron nitride mixed crystal (BN)_zP_1-z: A second buffer layer composed of 0 ≦ z ≦ 1) and having a gradient in the composition of the group V elementSequentiallyA buffer layer formed by stacking layers, and a general structural formula mainly composed of cubic crystals formed on the buffer layer is GaN._qAs_1-qA group III nitride semiconductor layer represented by (0 <q <1),Above mismatch rate of 0.1% or less III The lattice constant of the group nitride semiconductor layer substantially matches the lattice constant of the surface composition of the second buffer layer;It is characterized by that.
[0022]
  The invention according to claim 5It is a compound semiconductor device, Comprising: It provided on the said buffer layer using the laminated structure in any one of Claim 1 to 4. III Group nitride semiconductor is GaN _q As _1-q (0 <q <1) is the lower cladding layer, GaInN is the light emitting layer, and GaN _q As _1-q A double heterojunction light-emitting structure with an upper cladding layer of (0 <q <1),It is characterized by that.
[0025]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
1 and 2 are diagrams schematically showing a configuration of a laminated structure according to the present invention. In FIG. 1, a laminated structure (epitaxial wafer) 10a of the present invention includes a cubic crystal substrate 1 and a boron gallium phosphide mixed crystal (B) formed on the crystal substrate 1._xGa_1-xA buffer layer 21 composed of P: 0 ≦ x ≦ 1), and a general structural formula mainly composed of cubic crystals formed on the buffer layer 21 is Al._pGa_qIn_rN_sM_1-sA group III nitride semiconductor layer 3 represented by a layer (0 ≦ p, q, r ≦ 1, p + q + r = 1, 0 <s ≦ 1, and symbol M represents a group V element other than nitrogen); It is a laminated structure provided.
[0026]
As shown in FIG. 2, the laminated structure 10b according to the present invention includes boron phosphide nitride on the crystal substrate 1 instead of the buffer layer 21 made of a gallium phosphide mixed crystal in the laminated structure 10a shown in FIG. Mixed crystal (BN_zP_1-z: Buffer layer 22 composed of 0 ≦ z ≦ 1).
[0027]
First, the crystal substrate 1 in the laminated structures 10a and 10b will be described. As described above, the crystal substrate 1 is a substrate having a cubic crystal system. This is because the crystal system of the semiconductor layer 3 overlaid on the substrate 1 is made cubic dominant by using a cubic material from the base layer. Typical examples of the crystal structure of the cubic semiconductor of the crystal substrate 1 include a diamond type structure having a face centered cubic lattice and a zinc blend type structure. Silicon (Si) is a diamond-type semiconductor crystal. III-V group compound semiconductors such as gallium phosphide (chemical formula: GaP), gallium arsenide (chemical formula: GaAs), indium phosphide (chemical formula: InP), and indium arsenide (chemical formula: InAs) are zinc blende type semiconductor crystals. is there.
[0028]
Other cubic crystals that can be used as the crystal substrate 1 include rock salts such as magnesium oxide (chemical formula: MgO), manganese oxide (chemical formula: MnO), nickel oxide (chemical formula: NiO), and cobalt oxide (chemical formula: CoO). There are structural type oxides. Perovskite type lithium niobate (chemical formula: LiNbO_Three) And lithium tantalate (chemical formula: LiTaO)_ThreeOxide crystals such as) can also be used. In addition, LiGaO₂And LiAlO₂Such oxide crystals are also cubic crystals and can be used as the substrate 1.
An equiaxed cubic lattice metal crystal such as nickel (element symbol: Ni) can also be used as the substrate 1.
[0029]
Since the above oxide crystals are not cleaved or do not show clear cleaving properties ("SiC and related wide gap semiconductor research group 5th lecture (October 31 to November 1, 1996)" (Refer to Lecture No. IV-3, pages 20 to 21), it may be difficult to fabricate the resonant surface of the laser diode, possessing cleavage properties, substrate surface polishing technology, cleaning technology and large-diameter single crystal Judging from the viewpoint of practical technical level such as manufacturing technology, diamond (Si) having a diamond structure, zinc blende gallium arsenide (GaAs), gallium phosphide (GaP) and indium phosphide A semiconductor crystal such as (InP) is practically usable as the cubic substrate 1 according to the present invention.
A structure having a structure in which a cubic semiconductor layer is stacked on such face-centered cubic crystal can also be used as the substrate 1.
[0030]
A Si or GaAs crystal on which a drive circuit for driving a device, a circuit for controlling signal input / output, and the like are drawn can also be used as the substrate 1. If a cubic semiconductor crystal substrate 1 having such a drawing circuit is used, a composite device can be formed on the same substrate. As an example of this composite device, there is a device in which an LD and a PD, elements for driving and controlling them, a memory element for recording and storing an operation state, and the like are formed on a Si substrate.
[0031]
The conductivity type and conductivity (resistivity) of the material of the substrate 1 are not particularly limited. For example, a p-type silicon single crystal doped with boron (element symbol: B) or an n-type silicon single crystal doped with arsenic can be used as the substrate 1.
[0032]
For electronic devices such as MODFETs that require the need to electrically insulate the conductive active layer from the substrate crystal, a high resistance with a specific resistance (resistivity) of about several Ω · cm or more is required. Undoped silicon single crystal substrate and about 10^FiveA semi-insulating gallium arsenide single crystal exceeding Ω · cm can also be used as the substrate 1.
[0033]
There is no particular limitation on the plane orientation of the crystal surface used as the substrate 1. For example, conductive single crystal silicon to which boron, arsenic, or phosphorus having a {001} plane with an inclination angle in the [011] direction within ± 10 degrees can be used as the substrate 1. A zinc-doped p-type or silicon-doped n-type gallium arsenide single crystal is also suitable as the substrate 1.
[0034]
Next, the buffer layers 21 and 22 will be described. As described above, the buffer layer 21 includes the gallium borohydride mixed crystal (B_xGa_1-xP: 0 ≦ x ≦ 1), and the buffer layer 22 is composed of boron phosphide boron nitride mixed crystal (BN)_zP_1-z: 0 ≦ z ≦ 1).
[0035]
The first advantage of constructing the buffer layer 21 from the gallium phosphide mixed crystal and the buffer layer 22 from the phosphide boron nitride mixed crystal is that the gallium phosphide mixed crystal and the boron phosphide mixed nitride crystal are cubic crystals. In particular, it depends on the zinc-blende type crystal material. That is, from the viewpoint of the crystal type, the group III nitride semiconductor layer 3 stacked on the buffer layers 21 and 22 has an advantageous effect on the structure mainly composed of cubic crystals. Here, having a cubic crystal as a main component means that the volume ratio of the cubic crystal phase occupied in the growth layer is substantially over 95%.
[0036]
The second advantage is that the lattice constant of the buffer layer 21 can be arbitrarily controlled by adjusting the composition ratio of gallium and boron, which are group III constituent elements, in the gallium borohydride mixed crystal. In the phosphide boron nitride mixed crystal, the lattice constant of the buffer layer 22 can be arbitrarily controlled by adjusting the composition ratio of nitrogen and phosphorus which are Group V constituent elements. Therefore, for example, if the composition ratio is adjusted so that the lattice constants of these buffer layers 21 and 22 are matched with the lattice constants of the group III nitride semiconductor layer 3 stacked thereon, the buffer layers 21 and 22 and III The lattice matching with the group nitride semiconductor layer 3 can be made almost perfect.
If the composition ratio is adjusted so that the lattice constants of these buffer layers 21 and 22 match the lattice constants of the substrate 1, the lattice matching between the substrate 1 and the buffer layers 21 and 22 is almost complete. Can be.
[0037]
Next, the lattice constant control in the buffer layers 21 and 22 will be described in detail.
[0038]
First, the lattice constant of the buffer layer 21 will be described. The boron gallium phosphide mixed crystal (B_XGa_1-XBoron phosphide (BP) corresponding to the case where the boron composition ratio x = 1 in P) is a zinc blende type cubic crystal, and its lattice constant is 4.538%. B_XGa_1-XSimilarly, the gallium phosphide (GaP) corresponding to the boron composition ratio x = 0 in the P mixed crystal is a zinc blende type cubic crystal, and its lattice constant is 5.4495%. Therefore, B_XGa_1-XAs shown in FIG. 3, the range of the lattice constant L1 that the P (0 ≦ x ≦ 1) mixed crystal can take is 4.538 to 5.449, and the lattice constant L1 is less than the composition ratio x. It changes linearly.
[0039]
On the other hand, the lattice constant of the Si substrate 1 is 5.4309. Therefore, the above B_XGa_1-XP (0 ≦ X ≦ 1) is in the range of the lattice constant that the mixed crystal can take. This means that B_XGa_1-XThis means that the P mixed crystal can adopt a lattice constant that matches that of the Si substrate 1 depending on the composition ratio x of boron or the composition ratio (1-x) of gallium, that is, the composition ratio of the group III constituent elements. B with a boron composition ratio x of 0.02 (2%)_0.02Ga_0.98The lattice constant of the N mixed crystal is 5.4309Å when calculated from simple linear interpolation based on the Vegard law. Therefore, specifically, by setting the boron composition ratio x to 0.02, the BGaP buffer layer 21 that achieves lattice matching with the Si substrate 1 can be obtained. If the boron composition ratio x is 0 (zero), it naturally matches with GaP. That is, the buffer layer 21 is made B_XGa_1-XWhen composed of P (0 ≦ X ≦ 1) mixed crystal, there is an advantage that a buffer layer having a lattice matching relationship with Si or GaP practical as a cubic substrate material can be obtained.
[0040]
Next, the lattice constant of the buffer layer 22 will be described.boronMixed crystal layer (BN_zP_1-zAs described above, boron phosphide (BP) corresponding to the case where the nitrogen composition ratio z = 0 in (0 ≦ z ≦ 1)) is a zinc blende type cubic crystal, and its lattice constant is 4 .538cm. BN_zP_1-zBoron nitride (BN) corresponding to the case where the nitrogen composition ratio z = 1 in the mixed crystal is cubic and its lattice constant is 3.615%. Therefore, BN_zP_1-zAs shown in FIG. 4, the range of the lattice constant L2 that the (0 ≦ z ≦ 1) mixed crystal can take is 3.615 to 4.538 and the lattice constant L2 is linear with respect to the composition ratio z. Will change.
[0041]
BN mentioned above_zP_1-zWithin the range of lattice constants that (0 ≦ z ≦ 1) can be obtained, cubic GaN (lattice constant = 4.51 定 数) and zinc blende-type cubic BP (lattice constant = 4.538Å) , Cubic BN (lattice constant = 3.615Å), etc., and these GaN, BP, and BN can be used as the substrate 1. This means that BN_zP_1-zThe mixed crystal means that lattice matching with the cubic substrate 1 can be performed almost completely depending on the nitrogen composition ratio z or the phosphorus composition ratio (1-z). For example, BN with a nitrogen composition ratio z of 0.03 (3%)_0.03P_0.97The lattice constant of the mixed crystal is 4.51Å, so BN_0.03P_0.97The mixed crystal can be used as a constituent material of a buffer layer lattice-matched to the substrate 1 made of cubic GaN.
[0042]
In the embodiment according to the present invention, the buffer layers 21 and 22 may be formed as composition gradient layers. That is, in the buffer layer 21, the composition ratio x of boron, which is a Group III constituent element, is set to a layer thickness t from the substrate 1 to the Group III nitride semiconductor layer 3, as shown in FIG. A gradient is applied to form a composition gradient layer. Further, in the buffer layer 22, the composition ratio z of nitrogen that is the Group V constituent element is set as shown in FIG. 6 with respect to the layer thickness t from the substrate 1 toward the Group III nitride semiconductor layer 3. A gradient is applied to form a composition gradient layer. In this way, by providing the composition gradient, the buffer layers 21 and 22 that can fulfill the lattice matching relationship at the junction interface between the substrate 1 and the group III nitride semiconductor layer 3 can be obtained.
[0043]
As an example, GaN is formed on a substrate 1 made of Si single crystal._0.87As_0.13A case where the group III nitride semiconductor layer 3 made of a mixed crystal is laminated will be described. In this case, the boron composition ratio x is 0.02 at the bonding interface side with the substrate 1 and the boron composition ratio x is 0.13 at the bonding interface with the group III nitride semiconductor layer 3 B_xGa_1-xThe P (0 ≦ x ≦ 1) composition gradient layer is composed of Si substrate 1 and GaN._0.87As_0.13It can be preferably used as a buffer layer lattice-matched with both the group III nitride semiconductor layer 3 made of a mixed crystal.
[0044]
Further, B is obtained by increasing the boron composition ratio x on the substrate 1 made of GaP single crystal from 0 to 1 in the increasing direction of the layer thickness t._XGa_1-XThe P (0 ≦ X ≦ 1) composition gradient layer includes the substrate 1 and GaN_0.02As_0.98  It can be used as a buffer layer having a lattice matching relationship at the junction interface with both the group III nitride semiconductor layer 3 made of a mixed crystal.
[0045]
Further, BN obtained by increasing the nitrogen composition ratio z from 0 in the increasing direction of the layer thickness on the crystal made of BP having a lattice constant of 4.538Å._zP_1-zThe (0 ≦ z ≦ 1) composition gradient layer is used as a buffer layer that lattice-matches at the junction interface between the BP crystal layer and the group III nitride semiconductor layer made of cubic AIN (lattice constant = 4.38 cm). it can.
[0046]
In the above description, the composition gradient in the buffer layers 21 and 22 has been described as monotonically increasing with respect to the increasing direction of the layer thickness t, but this composition gradient is basically the substrate 1 and the group III nitride semiconductor layer 3. Therefore, it is not limited to a configuration that increases monotonously. For example, the buffer layers 21 and 22 may be configured to monotonously decrease in the increasing direction of the layer thickness t.
Further, the composition ratio x of the group III constituent elements in the buffer layer 21 is increased or decreased stepwise, and layers 21a, 21b,... Having different composition ratios x are stacked as shown in FIG. The laminated structure 10c may be configured by 21a, 21b,. Similarly, the composition ratio z of the group V constituent elements in the buffer layer 22 is increased or decreased stepwise, and layers 22a, 22b,... Having different composition ratios z are stacked as shown in FIG. The laminated structure 10d may be configured by the layers 22a, 22b,.
[0047]
In the embodiment according to the present invention, a new buffer layer can be configured by combining the buffer layers 21 and 22 having the composition gradient. For example, as shown in FIG. 9, the boron composition ratio x at the bonding surface with the substrate 1a is 0.02 (2%) on the surface of the substrate 1a made of Si single crystal, and the boron composition ratio at the surface layer surface. B where x is 1_XGa_1-XA first buffer layer 21m having a composition gradient made of P mixed crystal is deposited. Next, BN with a nitrogen composition ratio z of 0 at the joint surface with the first buffer layer 21m and a nitrogen composition ratio z of 0.03 at the surface layer surface_XP_1-XA second buffer layer 22m having a composition gradient composed of (0 ≦ X ≦ 1) mixed crystal is overlaid. By forming the buffer layers 21m and 22m having such a composition gradient, the lattice constant at the bonding surface with the Si substrate 1a becomes 5.4309Å, which matches the lattice constant of the Si substrate 1a. The lattice constant is 4.5100 mm, which matches the lattice constant of the cubic GaN layer 3a as the group III nitride semiconductor layer laminated thereon, and the laminated structure 10e having almost perfect lattice matching as a whole. Can be configured.
[0048]
As described above, the buffer layers 21m and 22m made of different materials are stacked to form a new buffer layer 23, whereby the range of selection of materials for the substrate 1 and the group III nitride semiconductor 3 can be expanded. For example, in the above example, B is formed on the Si single crystal substrate 1a._XGa_1-XEven if a single buffer layer made of P 2 mixed crystal is provided, a buffer layer that lattice-matches with cubic GaN (lattice constant = 4.51Å) cannot be formed. B_XGa_1-XThis is because the minimum lattice constant that P (0 ≦ x ≦ 1) can take is 4.538４．５ (the lattice constant of BP). However, as in the example above, BN_XP_1-XWhen buffer layers made of mixed crystals are stacked, a buffer layer lattice-matched with both Si as the substrate 1a and cubic GaN as the group III nitride semiconductor layer 3a is obtained. That is, even when single crystal Si is employed as the substrate, there is an advantage that the number of types of group III nitride semiconductor layers that can be stacked on the Si substrate while maintaining the lattice matching relationship can be increased.
[0049]
Conversely, when it is determined that the group III nitride semiconductor layer stacked on the buffer layer is made of cubic GaN, in the above example, not only the Si single crystal substrate 1a but also a substrate made of GaP is used. A buffer layer that matches the lattice can be formed. That is, the selection range of the substrate material can be expanded.
[0050]
In the above example, the composition gradient is applied to each layer of the buffer layer 23. However, the composition gradient may be applied to only at least one layer, or the layers may be stacked without applying the composition gradient. A configuration may be used, and the point is that any configuration that lattice-matches both the substrate 1 and the group III nitride semiconductor layer 3 may be used.
Further, although the buffer layer 23 is formed of two layers, it can be formed in a multilayer structure having more than that.
[0051]
Returning to FIGS. 1 and 2, the layer thickness of the buffer layers 21 and 22 will be described. There is no strict definition for the mechanical configuration such as the layer thickness of the buffer layers 21 and 22. If the buffer layers 21 and 22 are used as growth layers for inducing the growth of the group III nitride semiconductor layer 3 mainly composed of cubic crystals, the buffer layers 21 and 22 may be a monoatomic layer of several tens of meters. The effect can be demonstrated.
[0052]
Conversely, a relatively thick film of about several μm can also be used as the buffer layers 21 and 22. The reason why the buffer layers 21 and 22 can be thickened is as follows. That is, the buffer layers 21 and 22 of the present invention can be lattice-matched with the cubic substrate 1 by changing the composition of Group III or Group V constituent elements, and gradually increase the lattice constant. Can be changed. Therefore, as compared with the buffer layer having a single composition, the buffer layer inevitably has cracks due to lattice mismatch with the substrate 1 or the group III nitride semiconductor layer 3. This is because it is possible to suppress the situation that occurs.
[0053]
For example, even in the buffer layers 21 and 22 grown to a thickness of about several hundreds of μm by the halogen or hydride VPE method that can grow a relatively thick semiconductor layer, almost no cracks are observed on the surface. I can't. The buffer layers 21 and 22 of the present invention that achieve lattice matching with the substrate 1 and have almost no cracks on the surface even when the layer thickness is large are advantageous in forming a so-called high-luminance light-emitting device as described below.
[0054]
First, buffer layers 21 and 22 having a thickness of several tens to several hundreds of μm are formed on a substrate 1 made of Si single crystal. Since this Si single crystal has a small forbidden band width of about 1.1 electron volts (eV), it is a material that is opaque to visible short wavelength light. Next, the group III nitride semiconductor layer 3 that lattice-matches with the buffer layers 21 and 22 is stacked on the surfaces of the buffer layers 21 and 22 to complete the stacked structures 10a and 10b. Thereafter, the substrate 1 is removed by means such as chemical dissolution. In the present invention, since the buffer layers 21 and 22 can be made thick without causing cracks, the laminated structure 10a can be formed even if the substrate 1 is removed and the thick buffer layers 21 and 22 themselves are used as a supporting base. Therefore, the laminated structure 10a and 10b can be supported by the buffer layers 21 and 22 without causing any trouble in supporting 10b. This means that the so-called “substrate removal method” is used to remove the substrate material, which is a light-absorbing absorber, and to obtain an advantage of obtaining a high-luminance light-emitting device.
[0055]
Next, the conductivity of the buffer layers 21 and 22 will be described. The conductivity of the buffer layers 21 and 22 is not particularly specified, and may be determined in view of the function of the device and the direction of current flow for driving the device. Layers having n-type conductivity or p-type conductivity in which donor impurities or acceptor impurities are intentionally added (doping) can be used as the buffer layers 21 and 22. n-type conductive buffer layer, for example n-type BN_xP_1-xThe mixed crystal (0 ≦ x ≦ 1) 22 is a group IV impurity such as Si or tin (element symbol: Sn), selenium (element symbol: Se), sulfur (element symbol: S) or the like VI during film formation. It can be obtained by doping a group impurity. Also, a p-type conductive buffer layer such as p-type BN_xP_1-xThe mixed crystal 22 is obtained by doping Group II impurities such as zinc (element symbol: Zn), magnesium (element symbol: Mg), or group IV carbon (element symbol: C). These impurities have a carrier concentration which is an index of conductivity of about 1 × 10.¹⁷cm^-3Roughly 10¹⁹cm^-3It is preferable to dope so as to be within a range exceeding the range.
[0056]
The n-type or p-type buffer layers 21 and 22 are formed even if activation annealing is performed after the above-described impurities are implanted by the ion implantation method after the film formation instead of doping at the time of film formation. . For example, implantation of Si ions having a mass number of 28 or 29 and a valence of monovalent or divalent can be used to obtain the n-type buffer layers 21 and 22. Zn ion implantation can be used to obtain the p-type buffer layers 21 and 22. In the case of using the ion implantation method, the carrier concentration can be adjusted by the amount of ions implanted, the so-called dose amount. The range of doses that can be preferably used is usually approximately 1 × 10¹¹cm^-2~ 5x10¹³cm^-2The range of the degree. The distribution state of the carrier concentration in the depth direction (layer thickness direction) can be controlled by the ion acceleration voltage. An acceleration voltage of about 30 kilovolts (KV) to about 400 KV is commonly used. If the acceleration voltage is limited, the acceleration voltage can be reduced to half that of monovalent ions by selecting a method in which divalent ions of the same element are implanted instead of monovalent ions. If the acceleration energy given by the product of the valence of ions and the acceleration voltage is the same, the difference in distribution of the implanted atoms in the depth direction is not consequential.
[0057]
In the device in which the conductive material is the substrate 1 with the intention of laying electrodes on the back side of the substrate 1, the buffer layers 21 and 22 are also made of a conductive material.
[0058]
Depending on the device, high resistance layers doped with impurities so as to be undoped or electrically compensated for impurities are used as the buffer layers 21 and 22. The buffer layers 21 and 22 having high resistance can be obtained even by doping with transition metals such as iron (element symbol: Fe), chromium (element symbol: Cr), and vanadium (element symbol: V). After film formation, hydrogen ions (H⁺) (Proton) or the like can be injected to form a high-resistance buffer layer. It is desirable to use high resistance or insulating buffer layers 21 and 22 for a device that requires the isolation between the substrate 1 and the laminated layer 3. In a microwave device such as a field effect transistor (abbreviation: FET), the buffer layers 21 and 22 have about 10^FourA high resistivity exceeding Ω · cm is desirable.
[0059]
Next, the group III nitride semiconductor layer 3 will be described. On the buffer layers 21 and 22, as described above, Al is mainly composed of cubic crystals._pGa_qIn_rN_sM_1-sA group III nitride semiconductor layer 3 is laminated by stacking layers (0 ≦ p, q, r ≦ 1, p + q + r = 1, 0 <s ≦ 1 and the symbol M represents a group V element other than nitrogen). The bodies 10a and 10b are formed. Here, having a cubic crystal as a main component means that the volume ratio of the cubic crystal phase occupied in one crystal layer generally exceeds 95%.
[0060]
The material forming the group III nitride semiconductor layer 3 is a binary crystal (bielement crystal) such as GaN mainly composed of cubic crystals, aluminum nitride (chemical formula: AlN), indium nitride (chemical formula: InN), and the like. . Also, aluminum nitride / gallium mixed crystal (Al_aGa_bN: 0 ≦ a, b ≦ 1, a + b = 1), and a gallium nitride / indium mixed crystal mainly composed of cubic crystals (Ga_bIn_cN: 0 ≦ b, c ≦ 1, b + c = 1), and aluminum nitride / indium mixed crystal (Al_aIn_cN: 0 ≦ a, c ≦ 1, a + c = 1). Aluminum nitride, gallium, indium mixed crystals (Al_aGa_bIn_cN: 0 ≦ a, b, c ≦ 1, a + b + c = 1). Further, gallium arsenide mixed crystals (chemical formula: GaAsN), aluminum phosphide mixed nitride crystals (chemical formula: AlNP), and the like. That is, in the present invention, the general formula Al_pGa_qIn_rN_sM_1-s(0 ≦ p, q, r ≦ 1, p + q + r = 1, 0 <s ≦ 1, and the symbol M represents a Group V element other than nitrogen). In mixed crystals containing indium, the indium composition ratio may be uniform and difficult to form a compositionally homogeneous mixed crystal layer due to indium condensation due to heat, etc. Regardless of the degree of homogeneity, it is referred to as a mixed crystal layer for convenience.
[0061]
Each layer constituting the group III nitride semiconductor layer 3 may be n-type, p-type, or high-resistance i-type. For example, a group II element such as magnesium (element symbol: Mg), zinc (element symbol: Zn) or beryllium (element symbol: Be) is doped or diffused, or calcium (element symbol: Ca) is ion-implanted. P-type Al_pGa_qIn_rN_sM_1-sN-type Al formed by doping or ion implantation of a mixed crystal layer and a Group IV element such as Si, or a Group VI element such as selenium (element symbol: Se) or sulfur (element symbol: S)_pGa_qIn_rN_sM_1-sIf the mixed crystal layer is used as a constituent layer, it is possible to construct the laminated structures 10a and 10b for light-emitting devices or high-power thyristors that include a pn junction configuration.
[0062]
Both the substrate 1 and the buffer layer 21 or 22 are made to have high resistance._pGa_qIn_rN_sM_1-sThe stacked structures 10a and 10b formed by stacking an n-type channel layer and an n-type contact layer made of a mixed crystal can be used for Schottky junction field effect transistor (MESFET) applications. Al is further interposed between the n-type channel layer (electron transit layer) and the n-type contact layer._pGa_qIn_rN_sM_1-sAmong the MESFETs, the stacked structures 10a and 10b formed by arranging n-type electron supply layers made of can be preferably used particularly for two-dimensional electron gas FET (TEGFET) applications.
[0063]
A compound semiconductor device is formed by laying input / output electrodes for device operation power supply after processing or surface treatment for device fabrication is performed on the laminated structures 10a and 10b including the substrate 1 Form. Among these compound semiconductor devices, FET-based devices such as MESFET and MODFET (TEGFET) are subjected to recess processing for arranging a Schottky junction gate electrode by a general wet or plasma etching method, and then the source. It can be formed by arranging n-type ohmic electrodes forming source and drain electrodes. Further, in a light emitting device such as an LED or an LD, a mesa process is performed in which a light emitting portion made of a pn junction is left in a mesa type, and both p-type and n-type ohmic electrodes are provided.
[0064]
In the present invention, since the substrate 1 is cubic, a conductive material can be used for the substrate 1. If the conductive substrate 1 is used in the light emitting device such as the LED or LD, one ohmic electrode can be laid on the back side of the substrate 1. In conventional LEDs and LDs that use sapphire, which is an electrical insulator, as a substrate, one electrode (mostly n-side electrode) is formed because it is necessary to install both p-type and n-type electrodes on the same main surface. It was necessary to delete the area required for the light emitting layer (see Jpn. J. Appl. Phys., 34 (1995), pages L1332 to L1335). In this embodiment, since either one of the n-side electrode and the p-side electrode can be laid on the back side of the substrate 1, it is not necessary to delete the light emitting area (pn junction area). Reduction can be avoided, and a light emitting device having a large light emitting area can be manufactured with the same chip size.
[0065]
The p-type ohmic electrode includes nickel (Ni), palladium (element symbol: Pd), silver (element symbol: Ag), platinum (element symbol: Pt), gold (element symbol: Au), gold / zinc (Au. It can be composed of a Zn) alloy, a gold / beryllium (Au / Be) alloy, or the like. The n-type ohmic electrode can be made of a metal material such as aluminum (element symbol: Al), titanium (element symbol: Ti), chromium (element symbol: Cr), or indium (element symbol: In).
[0066]
In order to construct the laminated structures 10a and 10b according to the present invention, the buffer layer 21 is formed on the surface of the substrate 1 made of a cubic crystal material by the epitaxial film forming means described in the following (a) to (e). (22) and the group III nitride semiconductor layer 3 is grown.
(A) Phosphine (chemical formula: PH_Three), Ammonia (chemical formula: NH_Three) And diborane (chemical formula: B₂H₆) And the like as raw materials for Group V elements, trimethylgallium (chemical formula: (CH_Three)_ThreeAtmospheric pressure (atmospheric pressure) or reduced pressure organometallic pyrolysis vapor deposition (MOCVD) method (also referred to as MOVPE method or OMVPE method) using an organometallic compound such as Ga) as a group III element material.
(B) Arsenic trichloride (chemical formula: AsCl_Three) And boron trichloride (chemical formula: BCl_Three) And other group V element chlorides and metal gallium (element symbol: Ga) as raw materials, halide vapor phase epitaxy (VPE) method.
(C) Hydride VPE method using hydrides of Group V elements such as arsine, ammonia, diborane and metal gallium as raw materials
(D) Molecular beam epitaxial growth (MBE) method using metal gallium and arsenic as raw materials
(E) Gas-source MBE method using a gaseous raw material such as ammonia or hydrazine and a metal raw material.
[0067]
As described above, in the embodiment according to the present invention, the laminated structure 10a laminated on the substrate 1 includes the cubic crystal substrate 1 and the boron gallium phosphide mixed crystal formed on the crystal substrate 1. And the group III nitride semiconductor layer 3 formed on the buffer layer 21, the buffer layer 21 has a lattice defect between the substrate 1 and the group III nitride semiconductor layer 3. It has a function of relaxing the consistency and actively making the crystal system of the group III nitride semiconductor layer 3 a layer mainly composed of cubic crystals. Therefore, the entire laminated structure 10a is lattice-matched. It can be set as the structure which has a favorable cubic crystal.
[0068]
And since the whole can be comprised with a cubic crystal, it becomes difficult to generate | occur | produce a piezoelectric effect, and when forming a device from this laminated structure 10a, it can contribute greatly in ensuring the high-speed responsiveness as the device. .
[0069]
Further, since it is cubic, a low-resistance p-type conductive layer can be easily formed, and thus an pn junction structure is required, for example, an optical device such as an LED or LD, or an electronic device such as a high-power thyristor. Can be formed easily.
[0070]
Further, since the buffer layer 21 is composed of a gallium boron phosphide mixed crystal, the lattice constant can be arbitrarily controlled by adjusting the boron composition ratio x. Therefore, the group III nitride laminated thereon is provided. Almost complete lattice matching with the semiconductor layer 3 can be obtained, and a laminated structure 10a having a high-quality active layer such as an active layer with few crystal defects is provided, and various characteristics as a device are greatly improved. Can be improved. For example, in a light emitting device, a light emitting device having excellent light emission characteristics such as light emission intensity can be obtained, and in an FET device, high mobility is caused by the improvement in crystallinity of a channel layer as an active layer. Expressed and transconductance (so-called g_m) And other important characteristics can be improved.
[0071]
Further, since the composition ratio x of boron constituting the buffer layer 21 is given a gradient, the buffer layer 21 has almost perfect lattice matching not only with the group III nitride semiconductor layer 3 but also with the substrate 1 side. Therefore, the entire laminated structure 10a can be constructed with almost perfect lattice matching.
[0072]
Further, since the buffer layer 21 is formed by stacking layers 21a, 21b,... Having different boron composition ratios x constituting the buffer layer 21, the buffer layer 21 is formed by stacking layers having different lattice constants. Accordingly, crystal strains having different lattice constants are included therein, and therefore, crystal defects such as dislocations can be prevented from propagating to the upper group III nitride semiconductor layer 3, and the group III nitride semiconductor layer 3 having excellent crystallinity can be prevented. Can be laminated.
[0073]
In the embodiment according to the present invention, the laminated structure 10b formed on the substrate 1 is divided into a cubic crystal substrate 1 and a buffer layer made of boron phosphide mixed crystal formed on the crystal substrate 1. 22 and the group III nitride semiconductor layer 3 formed on the buffer layer 22, the buffer layer 22 relaxes the lattice mismatch between the substrate 1 and the group III nitride semiconductor layer 3. In addition, it has an effect of making the crystal system of the group III nitride semiconductor layer 3 a layer mainly composed of cubic crystals. Therefore, the entire laminated structure 10b is composed mainly of cubic crystals. It can be.
[0074]
And since the whole can be comprised with a cubic crystal, there exists an effect similar to the case of said laminated structure 10a.
[0075]
That is, the piezoelectric effect hardly occurs, and when a device is formed from the laminated structure 10b, it can greatly contribute to securing high-speed response as the device.
Further, since it is cubic, a low-resistance p-type conductive layer can be easily formed, and thus an pn junction structure is required, for example, an optical device such as an LED or LD, or an electronic device such as a high-power thyristor. Can be formed easily.
[0076]
Further, since the buffer layer 22 is composed of a phosphide boron nitride mixed crystal, the lattice constant can be arbitrarily controlled by adjusting the nitrogen composition ratio z, and therefore, the group III nitride laminated thereon is provided. Almost complete lattice matching with the semiconductor layer 3 can be obtained, resulting in a laminated structure 10b having a functional layer such as a high-quality active layer with few crystal defects, and various characteristics as a device are greatly improved. Can be improved. For example, in a light emitting device, a light emitting device having excellent light emission characteristics such as light emission intensity can be obtained, and in an FET device, high mobility is caused by the improvement in crystallinity of a channel layer as an active layer. Expressed and transconductance (so-called g_m) And other important characteristics can be improved. Various characteristics as a device can be greatly improved.
[0077]
In addition, since the composition ratio z of nitrogen constituting the buffer layer 22 is given a gradient, the buffer layer 22 exhibits almost perfect lattice matching not only with the group III nitride semiconductor layer 3 but also with the substrate 1 side. Therefore, the entire laminated structure 10b can be constructed with almost perfect lattice matching.
[0078]
Further, since the buffer layer 22 is formed by stacking layers 22a, 22b... Having different nitrogen composition ratios z constituting the buffer layer 22, the buffer layer 22 is formed by stacking layers having different lattice constants. Accordingly, crystal strains having different lattice constants are included therein, and therefore, crystal defects such as dislocations can be prevented from propagating to the upper group III nitride semiconductor layer 3, and the group III nitride semiconductor layer 3 having excellent crystallinity can be prevented. Can be laminated.
[0079]
In the embodiment according to the present invention, since the buffer layers 21 and 22 are stacked to form a new buffer layer 23, the buffer layer 23 can have a wider lattice constant. Therefore, even if the substrate 1 and the group III nitride semiconductor 3 to be joined above and below are selected from various materials, they can be joined under almost perfect lattice matching.
[0080]
In the above description, the group III nitride semiconductor layer 3 is directly stacked on the buffer layer 21 (or 22). However, as shown in FIG. B having almost the same composition_XGa_1-XP mixed crystal (or BN)_zP_1-zThe group III nitride semiconductor layer 3 can be laminated via the underlayer 41 (42) made of a mixed crystal, thereby forming the laminated structure 10f. According to this configuration, since the buffer layer / underlying layer becomes a pseudo homo junction, the occurrence of crystal defects such as dislocations due to misfit at the joining interface of both layers can be further suppressed. 41 (42) has a very small crystal defect density and is remarkably excellent in crystallinity. On such a foundation layer 41 (42), functional layers such as a cladding layer and an active (light-emitting) layer, which have inherited the high quality of the foundation layer 41 (42) and have further fewer crystal defects and a higher quality. Can be formed.
[0081]
Next, the laminated structure of the present invention and the compound semiconductor device formed from the laminated structure will be described with more specific examples.
[0082]
【Example】
In each of the following examples, a laminated structure having a heterojunction structure including a pn junction was first formed, and then an LED was formed from the laminated structure.
[0083]
(First embodiment)
FIG. 11 is a diagram showing a cross-sectional structure of the laminated structure in the first embodiment. In this embodiment, the buffer layer is B_xGa_1-xIt forms with P mixed crystal. In the figure, the laminated structure 100 is configured by being laminated on a substrate 101. The substrate 101 has a zinc blende type crystal structure, a resistivity of about 2 milliohm · centimeter (mΩ · cm), and a {100} 2 ° off gallium phosphide (GaP) single crystal. Using.
[0084]
On one main surface of the low-resistance and conductive substrate 101, B in a hydrogen stream at 750 ° C. by a general atmospheric pressure (atmospheric pressure) MOCVD method._xGa_1-xA low temperature buffer layer 121 made of P mixed crystal was deposited. B constituting the buffer layer 121_xGa_1-xThe boron (B) composition ratio x of the P (0 ≦ x ≦ 1) mixed crystal was set to 0 (zero) at the bonding interface with the substrate 101. That is, the buffer layer 121 in contact with the surface of the substrate 101 is made of the same GaP as the substrate 101. Diborane (Chemical formula: B₂H₆) / Phosphine (chemical formula: PH)_Three) / Trimethylgallium (chemical formula: (CH_Three)_ThreeUsing the MOCVD reaction system consisting of Ga)), the film formation was continued for 20 minutes, and the buffer layer 121 having a layer thickness of about 2000 mm was formed. Trimethylgallium ((CH) as a gallium (Ga) source to be supplied to the MOCVD reaction system during a film formation period of 20 minutes._Three)_ThreeBoron source diborane gas (10 vol% B) for Ga)₂H₆-90% by volume H₂) Supply ratio was reduced uniformly over time. At the end of the formation of the buffer layer 121, the supply of trimethylgallium to the MOCVD reaction system is stopped, the gallium composition ratio (1-x) is set to 0 (zero), and the boron composition ratio x is set to 1.0. did. By changing the supply flow rate of the Group III constituent element, the surface of the buffer layer 121 was changed to boron phosphide (BP). In 20 minutes required for the formation of the buffer layer 121, phosphine gas (10 vol% PH_Three-90% volume H₂) And disilane gas supplied to the MOCVD reaction system were not changed and kept constant. In addition, during the film formation period, about 5 ppm of disilane (chemical formula: Si₂H₆The buffer layer 121 having a composition gradient in which the boron composition ratio x is increased from 0 to 1.0 in the increasing direction of the layer thickness is doped with silicon (Si) using a disilane-hydrogen mixed gas containing) as a doping gas. By this Si doping operation, n-type conductivity was imparted to the buffer layer 121.
[0085]
Next, group III nitride semiconductor layers 131, 132, and 133 mainly composed of cubic crystals were sequentially stacked on the buffer layer 121. That is, after the film formation of the buffer layer 121 is completed, the arsenic (As) composition ratio is set to 0 in a hydrogen stream on the buffer layer 121 that is BP on the surface while the temperature of the substrate 101 is maintained at 750 ° C. 0.02 cubic n-doped Si-doped gallium arsenide nitride mixed crystal layer (GaN)_0.98As_0.02) As a lower cladding layer 131. The lattice constant of the lower clad layer 131 is 4.533 、, which substantially coincides with the lattice constant of 4.538Å of the BP forming the buffer layer 121. Arsine (AsH) is used as the arsenic (As) raw material when the lower cladding layer 131 is deposited._Three) Mixed gas (10 vol% AsH_Three-90% volume% hydrogen) was utilized. The above disilane-hydrogen mixed gas was used as a Si doping source. The thickness of the lower cladding layer 131 is about 1.5 μm, and the carrier concentration is about 2 × 10.¹⁸cm^-3It was.
[0086]
Next, an Si-doped gallium nitride / indium mixed crystal (Ga) having an indium composition ratio of 0.06 (6%) on the lower cladding layer 131 at 750 ° C._0.94In_0.06N) as the n-type light emitting layer 132, trimethylindium (chemical formula: (CH_Three)_ThreeLamination was performed by an atmospheric pressure MOCVD method using In) as an indium (In) source. Ga_0.94In_0.06The layer thickness of the N light emitting layer 132 is about 70 mm, and the carrier concentration is about 1 × 10 6.¹⁸cm^-3It was.
[0087]
Furthermore, a p-type gallium arsenide nitride mixed crystal (GaN) doped with Mg having a layer thickness of about 1000 mm by an atmospheric pressure MOCVD method at 750 ° C._0.98As_0.02) As the upper cladding layer 133 on the light emitting layer 132 made of an n-type gallium nitride / indium mixed crystal. P-type GaN forming the upper cladding layer 133_0.98As_0.02  Since the mixed crystal layer is mainly composed of cubic crystals, the hole concentration is also about 1 × 10.¹⁸cm^-3A high concentration of was easily reached.
[0088]
On the upper cladding layer 133, a contact layer 105 made of p-type boron phosphide (BP) doped with zinc (Zn) was laminated. Zinc is diethyl zinc (chemical formula: (C₂H_Five)₂A mixture of diethyl zinc and hydrogen containing about 100 ppm of Zn) 2 by volume was doped as a doping source. The thickness of the Zn-doped p-type BP contact layer 105 is about 500 mm, and the hole concentration is about 2 × 10.¹⁸cm^-3It was. Since BP is originally a zinc blende type cubic crystal, 10¹⁸cm^-3The p-type layer was a low-resistance layer exceeding 1.
[0089]
Through the above stacking operation, the lattice matching with the single crystal material constituting the substrate 101 and the lattice matching with the lower clad layer 131 are performed on the cubic GaP single crystal substrate 101 and between the substrate 101 and the lower clad layer 131. Of a pn junction type DH (double hetero) structure for LED use, which is provided with a buffer layer 121 that is effective in alleviating the lattice mismatch of the LED and is laminated on the buffer layer 121 while maintaining the lattice matching relationship. A structure 100 was formed.
[0090]
An LED that emits short-wavelength visible light was manufactured using the laminated structure 100 as a base material.
FIG. 12 is a diagram showing a cross-sectional structure of the LED in the first embodiment. In the figure, the LED 101 was formed by the following procedure. First, a metal film composed of three layers of gold (Au) / germanium (Ge) alloy (Au 95 wt%: Ge 5 wt%) / Ni / Au is sequentially formed on the back side of the GaP single crystal serving as the substrate 101. The n-type ohmic electrode 109 was formed by depositing by vacuum vapor deposition and performing an alloy treatment at 450 ° C. for 10 minutes in a hydrogen atmosphere.
[0091]
Next, a gold (Au) / zinc (Zn) alloy having a thickness of about 2000 mm (Au 97 wt%: Zn 3) is formed on the surface of the contact layer 105 made of p-type boron phosphide, which is the outermost layer of the laminated structure 100. % By weight) film, a nickel (Ni) film of about 1000 mm, and a gold (Au) film of about 1 μm were sequentially deposited by a normal vacuum deposition method. A metal film having an Au.Zn / Ni / Au three-layer multilayer structure was left in a circular shape having a diameter of 120 .mu.m at a constant pitch (interval) of 370 .mu.m by patterning using a general photolithography technique.
[0092]
Thereafter, an alloying process was performed for 2 minutes at 450 ° C. in a hydrogen atmosphere with the metal film left in a circular shape on the contact layer 105. By this alloy process, a p-type ohmic electrode 108 formed by laminating three metal layers was formed.
[0093]
On the surface of the contact layer 105, a lattice-like stripe (band-like groove) having a pitch (interval) between center lines of 370 μm and a width of 20 μm is drawn using patterning by a general photolithography technique and a wet etching method. did. The stripes orthogonal to the lattice were provided in parallel to the [011] direction in which GaP cleaves. The stripe was provided so that the circular p-type ohmic electrode 108 was positioned at the center of a square lattice defined by them.
[0094]
A cutter with a diamond cutting blade was run along the stripe line and separated into square chips each having a side of about 350 μm by scribing. Originally, a zinc blende type equiaxed cubic GaP crystal having a cleavage property in the [011] direction was used as a substrate, and the stacked constituent layer was also composed of a cubic crystal layer. In addition, it was easy to cut the laminated structure 100 so as not to cause unnecessary chipping.
[0095]
Individually separated chips are mounted (supported) inside a conical reflective cup (cup) that is attached with silver (Ag) provided on a stem (pedestal) to increase the efficiency of reflection of emitted light to the outside. did. Next, an LED 101 was formed by enclosing a cylindrical outer shape with a general transparent epoxy resin for sealing semiconductor elements.
[0096]
An operating current was passed in the forward direction between the p-type and n-type ohmic electrodes laid above and below the LED 101 via the anode and cathode lead terminals provided on the stem. The LED 101 emitted blue light due to the current flow in the forward direction. The central wavelength of light emission was about 4300 mm, and the half width of the emission spectrum was about 70 mm. The secondary emission spectrum in the near-ultraviolet region was not particularly measured, and the emission was excellent in monochromaticity. When the forward current was 20 milliamperes (mA), the light emission output was about 840 millicandelas (mcd), and the LED was excellent in light emission intensity. The forward voltage was about 4.2 volts (V) when 20 mA was applied. From the above, it has been suggested that the laminated structure 100 according to the present invention results from the LED 101 having excellent light emission characteristics such as light emission intensity and light emission monochromaticity.
[0097]
(Example 2)
FIG. 13 is a view showing a laminated structure in the second embodiment. In this embodiment, the buffer layer is BN_zP_1-zIt forms as a mixed crystal. In the figure, the laminated structure 200 is configured by being laminated on a substrate 201. The substrate 201 is composed of a lower layer substrate 201a and a surface layer side substrate 201b. That is, the substrate 201a is an n-type {001} -Si single crystal doped with phosphorus which is turned off by 4 ° in the [011] direction, and boron trichloride (BCl) is formed on the surface of the substrate 201a._Three) And phosphorus trichloride (PCl)_Three) By a general VPE method using boron and phosphorus sources, respectively, and depositing a Si-doped n-type BP layer having a thickness of about 2 μm at 800 ° C., and forming an n-type BP layer having this zinc blende type crystal form. The substrate 201b on the surface layer side was used.
[0098]
On one main surface of the substrate 201b, zincblende BN is formed at 800 ° C. by a general atmospheric pressure MOCVD method._zP_1-zA buffer layer 222 made of a mixed crystal was laminated. Trimethylboron (chemical formula: (CH_Three)_ThreeB) / Ammonia (NH_Three) / Phosphine (10% by volume PH)_Three-90% H₂) BN using reaction system_zP_1-zIn growing a mixed crystal layer (0 ≦ z ≦ 1), in order to lattice match with the BP layer forming the substrate 201b on the surface layer side, supply of ammonia gas to the reaction system at the initial stage of growth of the buffer layer 222 The amount was 0 (zero), that is, the composition ratio z of nitrogen was 0. As a result, the substrate 201b on the surface layer side and the buffer layer 222 are both made of BP, and the lattice matching is almost completely achieved.
[0099]
As the time spent for growing the buffer layer 222 elapses, that is, as the layer thickness of the buffer layer 222 increases, the nitrogen composition ratio z increases monotonically and gradually, finally reaching 0.02 (2%). did. BN with a layer thickness of about 200 mm_zP_1-zThe growth of the buffer layer 222 made of 10 minutes took 10 minutes, but during this time, only the supply amount of ammonia gas to the reaction system was increased, and the nitrogen composition ratio z was changed so as to change from 0 to 0.02. Was attached. Also during this growth period, Si was doped using the disilane-hydrogen mixture of the first embodiment, and the buffer layer 222 was made n-type.
[0100]
Next, group III nitride semiconductor layers 231, 232 and 233 mainly composed of cubic crystals were sequentially stacked on the buffer layer 222. That is, the surface composition is BN_0.02P_0.98After the film formation of the buffer layer 222 is completed, the surface of the buffer layer 222 is formed on the surface thereof at a temperature of 740.degree. Doped n-type gallium arsenide mixed crystal layer (GaN_0.99As_0.01) As a lower cladding layer 231. The film formation was performed by the atmospheric pressure MOCVD method using the arsine-hydrogen mixed gas described in the first example as an arsenic (As) source and the disilane-hydrogen mixed gas as a Si doping source. The thickness of the lower cladding layer 231 is about 2 μm, and the carrier concentration is about 3 × 10.¹⁸cm^-3It was. The lower cladding layer 231 has a lattice constant of 4.521Å, and the surface composition BN of the buffer layer 222_0.02P_0.98Is substantially equal to the lattice constant of 4.520 Å.
[0101]
GaN_0.99As_0.01On the lower clad layer 231, an Si-doped n-type gallium nitride / indium mixed crystal layer (Ga) mainly composed of cubic crystals having an indium composition ratio of 0.02 (2%) at 740 ° C._0.98In_0.02N) was laminated as the light emitting layer 232. The thickness of the light emitting layer 232 was about 1000 mm. The carrier concentration of the light emitting layer 232 is about 5 × 10¹⁷cm^-3In order to obtain the above, the doping flow rate of the disilane-hydrogen mixed gas was adjusted.
[0102]
On the n-type light emitting layer 232, a p-type gallium arsenide nitride mixed crystal layer (GaN) doped with Mg and having an arsenic (As) composition ratio of 0.01 (1%)._0.99As_0.01And the upper clad layer 233. Film formation was performed at 740 ° C. The thickness of the upper cladding layer 233 is about 5000 mm, and the carrier concentration is about 8 × 10¹⁷cm^-3It was. GaN of upper cladding layer 233_0.99As_0.01In the X-ray precision diffraction measurement method for the mixed crystal layer, a diffraction peak attributed to the hexagonal crystal was not observed.
[0103]
Through the above stacking operation, the lattice between the substrate 201 and the lower cladding layer 231 is lattice-matched to the material constituting the substrate 201b on the surface layer side and lattice-matched to the lower cladding layer 231 on the cubic substrate 201. A laminated structure of a pn junction type DH (double hetero) structure for LED use, which has a buffer layer 222 effective for alleviating mismatching, and is laminated on the buffer layer 222 while maintaining a lattice matching relationship. 200 was formed.
[0104]
An LED that emits near-ultraviolet light was manufactured using the laminated structure 200 as a base material.
FIG. 14 is a diagram showing a cross-sectional structure of the LED in the second embodiment. In the figure, the LED 201 was formed as follows. P-type gallium arsenide mixed crystal (GaN) that forms the outermost layer of the multilayer structure 200_0.99As_0.01The p-type ohmic electrode 208 having a three-layer structure of Au.Zn / Ni / Au is provided on the surface of the upper clad layer 233 made of) in accordance with the method and procedure described in the first embodiment. The n-type ohmic electrode 209 was composed of a coating film made of Au alone vacuum-deposited on the back side of the lower substrate 201 made of n-type Si single crystal.
[0105]
Thereafter, a chip was formed according to the cutting method described in the first embodiment, and the LED 201 was formed by molding with a transparent epoxy resin for sealing a semiconductor element. Thereafter, a direct current was passed between the n-type and p-type ohmic electrodes in the forward direction, and the light emission characteristics of the LED 201 were investigated. The emission wavelength was about 380 nm. The half width of the emission spectrum was about 160 mm. A secondary spectrum in the ultraviolet band, yellow, and red band was not observed, and the LED exhibited light emission excellent in monochromaticity. The forward voltage was about 4V when the forward voltage was 20 mA. Luminous output measured normally using a general integrating sphere (luminance (cd / cm²) × light emission area) is as high as about 500 millicandelas (mcd), and according to the present invention, it is not necessary to delete the light emitting surface in order to form electrodes as in the prior art, and the light emission area can be kept wide For this reason, it has been proposed that a high-output light-emitting device can be formed in combination with the original light emission intensity resulting from the lattice-matched laminated structure.
[0106]
【The invention's effect】
  Since this invention consists of an above-described structure, there can exist an effect which is demonstrated below.
  ThisIn this invention, a stacked structure formed on a substrate is made of a cubic crystal substrate and a boron gallium phosphide mixed crystal formed on the crystal substrate.First III Gradient composition of group elementsBuffer layer and formed on the buffer layerThe general structural formula is mainly GaN with cubic structure. _q As _1-q (0 <q <1)Group III nitride semiconductorWith a mismatch degree of 0.1% or less III So that the lattice constant of the group nitride semiconductor layer substantially matches the lattice constant of the surface composition of the buffer layerSince it is configured, the buffer layer relaxes the lattice mismatch between the crystal substrate and the group III nitride semiconductor layer, and the crystal system of the group III nitride semiconductor layer is a layer mainly composed of cubic crystals. Therefore, the entire laminated structure can be mainly composed of cubic crystals having good lattice matching.
[0107]
And since the whole can be comprised with a cubic crystal, it becomes difficult to generate | occur | produce a piezoelectric effect, and when forming a device from this laminated structure, it can contribute greatly in ensuring the high-speed responsiveness as the device.
[0108]
Further, since it is cubic, a low-resistance p-type conductive layer can be easily formed, and thus an pn junction structure is required, for example, an optical device such as an LED or LD, or an electronic device such as a high-power thyristor. Can be formed easily.
[0110]
  Moreover, in this invention, a buffer layer is comprised.Gallium phosphide mixed crystalSince the composition ratio of the group III element is given a gradient, the buffer layer can have almost perfect lattice matching not only with the group III nitride semiconductor layer but also with the crystal substrate side. The entire laminated structure can be built with almost perfect lattice matching.As a result, a laminated structure having a functional layer such as a high-quality active layer with few crystal defects can be provided, and various characteristics as a device can be greatly improved. For example, in a light emitting device, a light emitting device having excellent light emission characteristics such as light emission intensity can be obtained, and in an FET device, high mobility is caused by the improvement in crystallinity of a channel layer as an active layer. Expressed and transconductance (so-called g _m ) And other important characteristics can be improved.
[0112]
  In this invention, a laminated structure formed on a substrate is formed of a cubic crystal substrate and a boron phosphide mixed boron crystal formed on the crystal substrate.A gradient was added to the composition of Group V elementsBuffer layer and formed on the buffer layerThe general structural formula is mainly GaN with cubic structure. _q As _1-q (0 <q <1)A group III nitride semiconductor layer;With a mismatch of 0.1% or less III So that the lattice constant of the group nitride semiconductor layer substantially matches the lattice constant of the surface composition of the buffer layerSince it is configured, the buffer layer relaxes the lattice mismatch between the crystal substrate and the group III nitride semiconductor layer, and the crystal system of the group III nitride semiconductor layer is a layer mainly composed of cubic crystals. Therefore, the entire laminated structure can be mainly composed of cubic crystals.
[0113]
And since the whole can be comprised with a cubic crystal, it becomes difficult to generate | occur | produce a piezoelectric effect, and when forming a device from this laminated structure, it can contribute greatly in ensuring the high-speed responsiveness as the device.
Further, since it is cubic, a low-resistance p-type conductive layer can be easily formed, and thus an pn junction structure is required, for example, an optical device such as an LED or LD, or an electronic device such as a high-power thyristor. Can be formed easily.
[0115]
  In addition, since the composition ratio of the group V elements constituting the buffer layer is given a gradient, the buffer layer has almost perfect lattice matching not only with the group III nitride semiconductor layer but also with the crystal substrate side. Therefore, the entire laminated structure can be constructed with almost perfect lattice matching.In addition, various characteristics as a device can be greatly improved.
[0117]
  In the present invention, the buffer layer is overlaid with layers having different composition ratios of the group V elements constituting the buffer layer.By adding a gradient to the compositionAs a result, by stacking layers with different lattice constants, crystal strains with different lattice constants are included in the buffer layer, and therefore crystal defects such as dislocations propagate to the upper group III nitride semiconductor layer. Thus, a group III nitride semiconductor layer having excellent crystallinity can be laminated.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing a configuration of a laminated structure according to the present invention.
FIG. 2 is a diagram schematically showing a configuration of a laminated structure according to the present invention.
FIG. 3 shows a gallium borohydride mixed crystal (B_XGa_1-XIt is a figure which shows the relationship between the boron composition ratio x of P), and the lattice constant L1.
FIG. 4 shows boron phosphide mixed boron crystal (BN)._ZP_1-ZIs a diagram showing the relationship between the nitrogen composition ratio Z and the lattice constant L2.
FIG. 5 is a diagram showing a relationship between a layer thickness and a boron composition ratio when a gradient is given to a boron composition of a buffer layer made of a gallium borohydride mixed crystal.
FIG. 6 is a diagram showing a relationship between a layer thickness and a nitrogen composition ratio when a gradient is given to a nitrogen composition of a buffer layer made of a boron phosphide boron nitride mixed crystal.
FIG. 7 is a view showing a laminated structure having a buffer layer made of a gallium boron phosphide mixed crystal formed by stacking layers having different boron composition ratios.
FIG. 8 is a view showing a laminated structure having a buffer layer made of a boron phosphide mixed nitride crystal formed by stacking layers having different nitrogen composition ratios.
FIG. 9 is a view showing a laminated structure having a buffer layer formed by stacking a layer made of a gallium phosphide gallium phosphide mixed crystal and a layer made of a phosphide boron nitride mixed crystal.
FIG. 10 is a view showing a laminated structure formed by forming a base layer on a buffer layer.
FIG. 11 is a diagram showing a cross-sectional structure of the laminated structure in the first example.
FIG. 12 is a diagram showing a cross-sectional structure of an LED in the first embodiment.
FIG. 13 is a diagram showing a cross-sectional structure of a laminated structure in a second example.
FIG. 14 is a diagram showing a cross-sectional structure of an LED in a second embodiment.
[Explanation of symbols]
1 Substrate
21 Buffer layer made of gallium phosphide gallium phosphide mixed crystal
22 Buffer layer composed of boron phosphide boron nitride mixed crystal
3 Group III nitride semiconductor layer
10a Laminated structure
10b Laminated structure
10c, 10d, 10e, 10f Laminated structure
21a, 21b ... Buffer layers made of gallium borohydride mixed crystals with different boron composition ratios
22a, 22b ... Buffer layers made of phosphide boron nitride mixed crystals having different nitrogen composition ratios
21m Layer of gallium phosphide gallium phosphide mixed crystal
22m Layer consisting of boron phosphide boron nitride mixed crystal
23 Buffer layer consisting of 21m and 22m
41, 42 Underlayer
100 Laminated structure
101 substrate
105 Contact layer
108 p-type ohmic electrode
109 n-type ohmic electrode
110 LED
121 Buffer layer
131 Lower cladding layer
132 Light emitting layer
133 Upper cladding layer
200 Laminated structure
201a, 201b substrate
208 p-type ohmic electrode
209 n-type ohmic electrode
210 LED
222 Buffer layer
231 Lower cladding layer
232 Light emitting layer
233 Upper cladding layer
x Composition ratio of boron in gallium boron phosphide mixed crystal
z Composition ratio of nitrogen in phosphide boron nitride mixed crystal

Claims (5)

In a laminated structure formed by laminating on a substrate,
A cubic crystal substrate;
A buffer layer made of a gallium boron phosphide mixed crystal (B _x Ga _1-x P: 0 ≦ x ≦ 1) formed on the crystal substrate and having a gradient in the composition of the group III element;
A group III nitride semiconductor layer formed on the buffer layer and mainly composed of cubic crystals and having a general structural formula of GaN _q As _1-q (0 <q <1);
And the lattice constant of the group III nitride semiconductor layer substantially matches the lattice constant of the surface composition of the buffer layer when the degree of mismatch is 0.1% or less .
A laminated structure characterized by that. In a laminated structure formed by laminating on a substrate,
A cubic crystal substrate;
A buffer layer made of a boron phosphide boron nitride mixed crystal (BN _z P _1-z : 0 ≦ z ≦ 1) formed on the crystal substrate and having a gradient in the composition of the group V element;
A group III nitride semiconductor layer formed on the buffer layer and mainly composed of cubic crystals and having a general structural formula of GaN _q As _1-q (0 <q <1);
And the lattice constant of the group III nitride semiconductor layer substantially matches the lattice constant of the surface composition of the buffer layer when the degree of mismatch is 0.1% or less .
A laminated structure characterized by that. The buffer layer, the Rukoto is overlaid with differing layer composition ratio of the group V element constituting the buffer layer, and subjected to gradient in composition, multilayer structure according to claim 2. In a laminated structure formed by laminating on a substrate,
A cubic crystal substrate;
On the crystal substrate, a boron phosphide gallium mixed crystal _{(B x Ga 1-x P} : 0 ≦ x ≦ 1) and the first buffer layer composed denoted a gradient from the composition of the formed Ri group III element, A buffer layer formed by sequentially stacking a second buffer layer made of a boron phosphide boron nitride mixed crystal (BN _z P _1-z : 0 ≦ z ≦ 1) and having a gradient in the composition of the group V element;
A group III nitride semiconductor layer formed on the buffer layer and mainly composed of cubic crystals and having a general structural formula of GaN _q As _1-q (0 <q <1);
And the lattice constant of the group III nitride semiconductor layer substantially matches the lattice constant of the surface composition of the second buffer layer when the degree of mismatch is 0.1% or less .
A laminated structure characterized by that. The group III nitride semiconductor provided on the buffer layer using the multilayer structure according to any one of claims 1 to 4 , wherein GaN _q As _1-q (0 <q <1) is a lower cladding layer, A double heterojunction light-emitting structure with GaInN as the light-emitting layer and GaN _q As _1-q (0 <q <1) as the upper cladding layer,
The compound semiconductor device characterized by the above-mentioned.

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