JP5741350B2 - Light emitting element - Google Patents

Description

  The present invention relates to a light emitting device formed by stacking nitride semiconductors.

In nitride semiconductor elements having many threading dislocations, a Zener diode (protective element) is attached or a layer having a certain thickness and different resistance is nitrided for the purpose of maintaining or improving electrostatic breakdown voltage characteristics. It has been attempted to improve current diffusivity by inserting it into a semiconductor layer. However, the introduction of the protective element leads to an increase in cost, and there is a problem that a small product does not have a space for mounting the protective element. Further, when a layer having a different resistance is inserted into the nitride semiconductor layer, the current diffusibility is improved and the electrostatic withstand voltage characteristic is improved. At the same time, the threshold value of the forward voltage V _f is also increased by increasing the resistance. The problem of going up occurs.

JP 2006-128527 A International Publication No. 2008/117788 JP-A-8-70139

  In view of the above circumstances, an object of the present invention is to provide a light emitting element with improved electrostatic withstand voltage characteristics without increasing cost and threshold voltage.

In the light emitting device of the present invention, an n-side nitride semiconductor layer, an active layer, and a p-side nitride semiconductor layer are sequentially stacked on a substrate,
In a light emitting device in which an n-side electrode and a p-side electrode are provided on the n-side nitride semiconductor layer and the p-side nitride semiconductor layer, respectively.
The n-side nitride semiconductor layer has an n-type contact layer composed of an upper n-type contact layer and a lower n-type contact layer in contact with the n-type electrode;
Between the upper n-type contact layer and the lower n-type contact layer, an AlN layer having a composition different from that of the upper n-type contact layer and the lower n-type contact layer is provided.
The distance between the AlN layer and the n-side electrode is shorter than the distance between the AlN layer and the substrate.

  The distance between the AlN layer and the n-side electrode is preferably shorter than the thickness of the lower n-type contact layer. The distance between the AlN layer and the n-side electrode is preferably 0.1 μm to 3.0 μm, more preferably 0.1 μm to 2.0 μm, and still more preferably 0.1 μm to 1.0 μm.

  The thickness of the AlN layer is preferably 1 nm to 10 nm, more preferably 1 nm to 5 nm, and even more preferably 3 nm to 4 nm.

  The upper n-type contact layer and the lower n-type contact layer are preferably GaN layers.

  In the light emitting device of the present invention, an AlN layer having a different composition from the p-type contact layer is further provided in the p-side nitride semiconductor layer so as to be in contact with the p-type contact layer between the p-type contact layer and the active layer. Preferably it is.

  According to the light emitting device of the present invention, the n-type contact layer is in contact with an AlN layer (hereinafter also referred to as an n-side AlN layer) having a composition different from that of the n-type contact layer (that is, having a different band gap). Carrier mobility is increased at the interface between the n-type contact layer and the n-side AlN layer, and current diffusivity is improved. By diffusing current at the interface between the n-type contact layer and the n-side AlN layer, the relatively crystalline brittle active layer is protected and the electrostatic withstand voltage characteristics can be improved.

1A and 1B are conceptual diagrams showing a conventional light emitting device and FIG. 1B showing a light emitting device of the present invention. FIG. 2 is a graph showing the relationship between the insertion position of the n-side AlN layer of the light emitting device of the present invention and the electrostatic withstand voltage characteristics. FIG. 3 is a graph showing the measurement result of carrier mobility at the interface between undoped GaN and AlN. FIG. 4 is a graph showing the relationship between the thickness of the n-side AlN layer of the light emitting device of the present invention and the electrostatic withstand voltage characteristics. FIG. 5 is a graph showing the relationship between the thickness of the n-side AlN layer of the light emitting device of the present invention and the forward voltage _Vf .

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the embodiment described below exemplifies a mode for embodying the technical idea of the present invention, and the present invention is not limited to the following. The dimensions, materials, shapes, relative arrangements, and the like of the components described in the embodiments are not intended to limit the scope of the present invention only to the mere explanatory examples, unless otherwise limited. Not too much. Note that the size, positional relationship, and the like of the members shown in each drawing may be exaggerated for clarity of explanation. Furthermore, each element constituting the present invention may be configured such that a plurality of elements are configured by the same member and the plurality of elements are shared by one member, and the function of the one member is shared by the plurality of members. It can also be realized.

  FIG. 1 is a conceptual diagram of a conventional light emitting device (a) and a light emitting device (b) of the present invention. In the conventional light emitting device shown in FIG. 1A, on a substrate 1 made of sapphire, an n-side nitride semiconductor layer containing an n-type impurity such as Si, an active layer 3 and ap containing an p-type impurity such as Mg. The side nitride semiconductor layers 4 are sequentially stacked. The n-side nitride semiconductor layer includes an n-type contact layer 2. The n-side nitride semiconductor layer may include layers other than the n-type contact layer 2. A p-side electrode 5 including a p-side translucent electrode 5 a and a p-side pad electrode 5 b is formed on the p-side nitride semiconductor layer 4. An n-side electrode 6 is formed on the surface of the n-type contact layer 2 exposed by etching away the portion. On the other hand, the light emitting device of the present invention shown in FIG. 1B has an AlN layer 7 having a different composition between the lower and upper n-type contact layers between the lower n-type contact layer 2a and the upper n-type contact layer 2b. Is further provided.

  The n-type contact layer 2 and the n-side AlN layer 7 have different compositions from each other, and therefore have different lattice constants. Therefore, when a voltage is applied to the light emitting element, a piezo electric field is generated at the interface between the n-type contact layer 2 and the n-side AlN layer 7 due to the difference in lattice constant. Thereby, carrier mobility increases at the interface, and current is diffused laterally at the interface. Compared with the conventional light emitting element shown in FIG. 1A, how current is diffused in the light emitting element of the present invention is schematically shown by arrows in FIG. A current is diffused at the interface between the n-type contact layer 2 and the n-side AlN layer 7, so that a current is not concentrated and injected into a part of the active layer 3, and a relatively crystalline brittle active layer Is protected and the electrostatic withstand voltage characteristic is improved.

  Such an n-side AlN layer 7 may be an undoped AlN layer and is preferable because a semiconductor crystal can be grown at a stable mixed crystal ratio.

  In addition, the shorter the distance between the n-side AlN layer 7 and the n-side electrode 6, the easier the current flows in the vicinity of the interface with a higher carrier mobility, and the effect of current diffusion at the interface increases, so that the static Withstand voltage characteristics are improved. Therefore, when the nitride semiconductor layer is removed by etching in order to form the n-side electrode 6, the thickness of the upper n-type contact layer 2b remaining on the n-side AlN layer 7 is preferably as thin as possible. On the other hand, it is necessary to leave the upper n-type contact layer 2b having a constant thickness on the n-side AlN layer according to the etching accuracy. For this reason, the distance between the n-side AlN layer 7 and the n-side electrode 6 is preferably shorter than ½ of the distance between the substrate 1 and the n-side electrode 6. Specifically, the distance between the n-side AlN layer 7 and the n-side electrode 6 is 0.1 μm to 3.0 μm, preferably 0.1 μm to 2.0 μm, more preferably 0.1 μm to 1.0 μm. It is.

The thickness of the n-side AlN layer 7 is preferably 1.0 nm to 10 nm, more preferably 1.0 nm to 5.0 nm. When the thickness of the n-side AlN layer 7 is set in this way, the increase in carrier mobility at the interface between the n-side AlN layer 7 and the n-type contact layer 2 is remarkable, and therefore the electrostatic withstand voltage characteristic is efficiently improved. Can be made. In particular, the thickness of the n-side AlN layer 7 is more preferably 3.0 to 4.0 nm. When the thickness of the n-side AlN layer 7 is set to 3.0 nm or more, the n-side AlN layer 7 can be formed as a layer with few crystal defects, so that the electrostatic withstand voltage characteristic can be further improved. When the thickness of the n-side AlN layer 7 is 4.0 nm or less, even if the n-side AlN layer 7 having a relatively high resistance value is formed, an increase in threshold value in the forward voltage _Vf can be reduced.

  Further, in the p-side nitride semiconductor layer 4, an AlN layer having a composition different from that of the p-type contact layer (hereinafter also referred to as a p-side AlN layer) is in contact with the p-type contact layer between the p-type contact layer and the active layer. Thus, the electrostatic withstand voltage characteristic of the light emitting element can be further improved.

  The reason why the electrostatic withstand voltage characteristic is improved by inserting the p-side AlN layer is considered as follows. The composition of the p-type contact layer and the p-side AlN layer are different from each other, and thus the lattice constant is different. Therefore, when a voltage is applied to the light emitting element, the difference in the lattice constant at the interface between the p-type contact layer and the p-side AlN layer. A piezo electric field is generated due to. Thereby, carrier mobility increases at the interface, and current is diffused laterally at the interface. It is considered that the electrostatic withstand voltage characteristic is improved by the diffusion of the current.

Hereinafter, each configuration of an example of the light-emitting element according to the present invention will be described in detail. However, all the components described below are not essential, and some of them can be omitted or changed.
In the light emitting device of the present invention, an n-side nitride semiconductor layer, an active layer, and a p-side nitride semiconductor layer are sequentially stacked on a substrate, and a p-side translucent electrode and a p-side nitride semiconductor layer are formed on the p-side nitride semiconductor layer. A p-side electrode composed of a p-side pad electrode is formed, and an n-side electrode is formed on the surface of the n-type contact layer exposed by etching away a part of the nitride semiconductor layer from the p-side nitride semiconductor layer. .

〔substrate〕
As the substrate, an insulating substrate such as spinel (MgAl ₂ O ₄ ), a semiconductor substrate such as SiC, ZnS, ZnO, GaAs, and GaN can be used in addition to the C-plane, R-plane, and A-plane of sapphire.

[N-side nitride semiconductor layer]
The n-side nitride semiconductor layer according to this embodiment includes a buffer layer, a lower n-type contact layer, an n-side AlN layer, an upper n-type contact layer, an undoped semiconductor layer, and an n-type multilayer film layer in order from at least the substrate side. Has been.

(Buffer layer)
The buffer layer is formed on the substrate, and is a low-temperature growth layer for relaxing a mismatch in lattice constant between the substrate and the nitride semiconductor and forming a highly crystalline nitride semiconductor layer thereon. The buffer layer can finally be removed or can itself be omitted. Such a buffer layer is preferably formed by growing AlGaN, GaN, AlN or the like at a temperature of 500 to 800 ° C. to a thickness of 10 to 50 nm.

  Further, a second buffer layer may be further formed on the buffer layer. The second buffer layer has a smaller doping amount of n-type impurities than an n-type contact layer, which will be described later, or a nitride semiconductor not doped with n-type impurities, such as AlGaN, GaN, AlN, etc., than the first buffer layer described above. It is grown at a high temperature, for example, 800 to 1300 ° C. to a thickness of 0.5 to 3.0 μm. The second buffer layer has a high crystallinity because the impurity doping amount is small (or zero). Therefore, a highly crystalline lower n-type contact layer can be formed thereon.

(Lower and upper n-type contact layers)
The composition of the lower and upper n-type contact layers is not particularly limited, and is preferably a layer made of AlGaN or GaN having an Al ratio of 0.2 or less, for example. With such a composition, it is easy to obtain a nitride semiconductor layer with few crystal defects. The lower and upper n-type contact layers contain an n-type impurity such as Si, and the concentration is preferably high enough not to deteriorate the crystallinity of the nitride semiconductor. For example, it is 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less.
The lower n-type contact layer is formed by growing on the buffer layer at a temperature of 900 to 1300 ° C., but the film thickness is not particularly limited. For example, the sheet resistance can be reduced by setting the thickness to about 1.0 μm or more, preferably about 2.0 μm or more, but the thickness is set to 2.0 to 8.0 μm in consideration of reduction of the warpage of the wafer. It is preferable to do this.
The upper n-type contact layer is preferably formed so that an n-side AlN layer, which will be described later, is disposed closer to the n-side electrode than the substrate. For example, in consideration of the depth to which the upper n-type contact layer is etched when forming an n-side electrode described later, the thickness is about 1.0 to 4.0 μm at a temperature of 900 to 1300 ° C. on the n-side AlN layer. It is preferable to form it by growing it to a thickness.

(N-side AlN layer)
The n-side AlN layer is a layer for increasing the carrier mobility and diffusing the current flowing from the n-side electrode in the lateral direction at the interface between the lower and upper n-type contact layers. The n-side AlN layer is formed on the lower n-type contact layer by growing AlN having a different composition (or lattice constant) from the lower and upper n-type contact layers to a thickness of 1 to 10 nm. For example, when GaN is grown as the lower and upper n-type contact layers, AlN is grown as the n-side AlN layer. The n-side AlN layer can obtain a current diffusion effect regardless of whether or not n-type impurities are doped.

(Undoped semiconductor layer)
Examples of the undoped semiconductor layer include a layer made of In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). Among them, the undoped semiconductor layer is preferably Al _y Ga _1-xy N or In _x Ga _1-xy N having GaN, x and / or y of 0.2 or less, and further, a layer made of GaN. It is preferable to include. With such a composition, a nitride semiconductor layer with few crystal defects can be easily obtained.
The undoped semiconductor layer may be formed as a single layer, but is preferably formed as a multilayer. When the undoped semiconductor layer is formed in multiple layers, it is not necessary that all the layers be undoped layers that do not contain n-type impurities, and at least one layer may be an undoped layer. In particular, the undoped semiconductor layer is preferably a layer in which undoped layers and doped layers having the same composition are alternately stacked. These alternating lamination layers are, for example, preferably 3 layers or more, and suitably 5 layers or less, and any of the undoped layer and the doped layer may be the lowermost layer and / or the uppermost layer. Good. Specifically, a first layer made of undoped GaN having a thickness of 50 to 150 nm is grown on the upper n-type contact layer, and Si is formed thereon at 1 × 10 ^{18 to} 9 × 10 ¹⁸ / cm ^3. After the second layer of doped GaN having a thickness of 1 to 50 nm is grown and this is repeated twice, undoped GaN is further grown to a thickness of 1 to 10 nm, and the total thickness is 103 to 410 nm. An undoped semiconductor layer is formed. Thus, impurities are not doped, thus a high undoped GaN layer having a carrier mobility, impurity-doped, therefore by the high carrier concentration layer is present alternately, the threshold in the forward voltage V _f Decreases. The first layer may be Si-doped GaN having a smaller Si doping amount than the second layer.

In this specification, “undoped” is a layer formed without introducing impurities during film formation, and is diffused from the upper and lower layers after film formation and / or by heat treatment or the like in the manufacturing process. It does not mean the layer that was made. In other words, a layer having an impurity concentration of about 1 × 10 ¹⁷ / cm ³ or less is substantially referred to as an “undoped” layer.

(N-type multilayer film layer)
The n-type multilayer film layer is a nitride semiconductor composed of at least two kinds of elements having different compositions, for example, In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ a layer consisting of x + y ≦ 1). In particular, the n-type multilayer film layer is composed of Al _z Ga _1-z N (0 ≦ z <1) (first layer) and In _p Ga _1-p N (0 <p <1) (second layer). It is preferable that layers having two kinds of compositions are alternately laminated. The first layer is preferably a layer made of GaN with z = 0 because the smaller z, that is, the smaller the aluminum content, the better the crystallinity. The second layer is preferably a layer having p of 0.5 or less, and more preferably a layer having p of 0.2 or less. Among them, as the n-type multilayer film, a first layer is GaN, preferably p in the second layer is 0.2 or less of _{an In} p _{Ga 1-p} N.
Further, the film thickness of the single layer (that is, the first layer or the second layer) constituting the n-type multilayer film is not particularly limited, but it is suitable that the film thickness of at least one kind of single layer is 10 nm or less. 7 nm or less is preferable, and 5 nm or less is more preferable. More specifically, a first layer made of GaN having a thickness of 1 to 5 nm is grown on the undoped semiconductor layer, and a second layer made of InGaN and having a thickness of 0.5 to 3 nm is formed thereon. After growing and repeating this 20 times, GaN is further grown to a thickness of 1 to 5 nm to form an n-type multilayer film layer having a total film thickness of 31 to 165 nm. By reducing the film thickness of the single layer in this way, the n-type multilayer film layer has a superlattice structure and is less than the critical elastic film thickness, and the crystallinity of each single layer in the n-type multilayer film layer is improved. . Therefore, as the stacking progresses, the crystallinity can be further improved and the light output can be improved.

[Active layer]
Multi-quantum well structure or single quantum well having a nitride semiconductor comprising at least In, preferably a well layer containing In _x Ga _1-x N (0 ≦ x <1), and a barrier layer as an active layer A structure can be used. The film thickness of the well layer or the barrier layer is 30 nm or less, preferably 20 nm or less. In particular, the well layer is preferably thin, and is preferably 10 nm or less, more preferably 1 to 5 nm. As a result, an active layer having excellent quantum efficiency can be obtained.
When the active layer has a multiple quantum well structure, it is possible to improve the output and lower the oscillation threshold. If well layers and barrier layers are alternately stacked, the first and last layers may be well layers or barrier layers. Further, in the multiple quantum well structure, the barrier layer sandwiched between the well layers is not limited to a single layer (well layer / barrier layer / well layer), and two or more barrier layers. A plurality of barrier layers having different compositions, impurity amounts, and the like may be provided as “well layer / barrier layer (1) / barrier layer (2) /... / Well layer”.
The barrier layer is not particularly limited, and a nitride semiconductor having a lower In content than the well layer, a nitride semiconductor containing GaN, Al, or the like can be used. More preferably, it contains InGaN, GaN, or AlGaN. The thickness and composition of the barrier layer need not all be the same in the quantum well structure.

[P-side nitride semiconductor layer]
In the p-side nitride semiconductor layer according to the present embodiment, a p-side cladding layer and a p-type contact layer are laminated at least from the active layer side.

(P-side cladding layer)
The p-side cladding layer is a single layer or band gap energy composed of In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) containing a p-type impurity. And a laminated structure of at least two layers different from each other. Among these, a single layer made of Al _x Ga _1-x N (0 ≦ x ≦ 1) or a laminated structure of at least two layers having different band gap energies is preferable. For example, the p-side cladding layer in the present embodiment is formed by growing Mg-doped AlGaN to a thickness of 10 to 50 nm on the active layer and further growing undoped GaN to a thickness of 50 to 100 nm thereon. To do.
When the p-side cladding layer has a laminated structure, the thickness of each layer may be about 10 nm or less, and further about 7 nm or less and about 5 nm or less. By forming such a thin film, the p-side cladding layer has a superlattice structure, so that the crystallinity can be improved. As a result, when a p-type impurity is added, a layer having a high carrier concentration and a low resistivity is obtained, and the V _f and threshold value of the light emitting element tend to be lowered.
The p-side cladding layer has a p-type impurity concentration of, for example, preferably about 1 × 10 ²² / cm ³ or less, and more preferably about 5 × 10 ²⁰ / cm ³ or less. The lower limit of the p-type impurity concentration is not particularly limited, but about 5 × 10 ¹⁶ / cm ³ or more is suitable. However, in the laminated structure, the p-type impurity may not be contained in all the layers.

(P-side AlN layer)
In some cases, by providing an AlN layer (p-side AlN layer) having a composition different from that of the p-type contact layer between the aforementioned p-side cladding layer and a p-type contact layer described later, the electrostatic withstand voltage characteristics of the light-emitting element Can be further improved. The insertion position of the p-side AlN layer is not limited to this, and an effect of improving electrostatic withstand voltage characteristics can be obtained if the p-side AlN layer is provided so as to be in contact with the p-type contact layer between the p-type contact layer and the active layer. it can. The thickness of the p-side AlN layer is preferably 1 to 10 nm. Note that the p-side AlN layer can obtain a current diffusion effect regardless of the presence or absence of p-type impurity doping.

(P-type contact layer)
Examples of the p-type contact layer include a layer made of In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1). A layer composed of AlGaN of 0.2 or less and InGaN having an In ratio of 0.2 or less is preferable, and a layer composed of GaN is more preferable. These compositions can provide good ohmic contact with the electrode material.
The thickness of the p-type contact layer is not particularly limited, and is preferably about 50 nm or more, and more preferably about 60 nm or more.
Examples of the impurity concentration include 1 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less.

[P-side electrode and n-side electrode]
The p-side electrode and the n-side electrode are not particularly limited, and any of those known in the art can be adopted.
For example, the p-side electrode according to the present embodiment is configured by sequentially forming a p-side translucent electrode and a p-side pad electrode on a p-type contact layer. The p-side translucent electrode is preferably formed of a material that does not absorb light emitted from the active layer in consideration of light extraction efficiency. For example, a conductive oxide (ITO, ZnO, or the like) is used. Can be mentioned.
Further, the n-side electrode was exposed by exposing a part of the nitride semiconductor layer to a depth of about 1.0 to 1.5 μm from the p-side nitride semiconductor layer to expose the upper n-type contact layer. It is formed on the surface of the upper n-type contact layer. The distance between the n-side AlN layer and the n-side electrode is preferably shorter than ½ of the distance between the substrate and the n-side electrode. More specifically, the distance between the n-side AlN layer and the n-side electrode is 0.1 μm to 3.0 μm, more preferably 0.1 μm to 2.0 μm, still more preferably 0.1 μm to 1.0 μm. It is. Thereby, the current flowing from the n-side electrode easily flows in the vicinity of the interface with the n-side Al _X Ga _1-X N layer having a high carrier mobility, so that the electrostatic withstand voltage characteristic can be improved.

  Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[Example 1]
The light emitting device of Example 1 of the present invention was manufactured according to the following steps.

(substrate)
A substrate made of sapphire (C-plane) was set in a MOCVD reaction vessel, and the substrate temperature was raised to about 900 ° C. to 1200 ° C. while flowing hydrogen to clean the substrate.

(First buffer layer)
Subsequently, the temperature is lowered to about 500 to 800 ° C., hydrogen is used as a carrier gas, ammonia is used as a source gas, TMG (trimethylgallium) and TMA (trimethylaluminum) are used to form undoped AlGaN on the substrate to a thickness of about 20 nm. A first buffer layer was formed by growth.

(Second buffer layer)
After forming the first buffer layer, only TMA is stopped, the temperature is raised to about 800-1300 ° C., and then undoped GaN is grown to a thickness of about 2.0 μm using TMG and ammonia gas as source gases. The second buffer layer was formed.

(N-type contact layer and n-side AlN layer)
Next, at a temperature of about 900 to 1300 ° C., TMG and ammonia are used as the source gas, and silane is used as the impurity gas, and GaN doped with Si of 4.5 × 10 ¹⁸ / cm ³ is grown to a thickness of about 2.0 μm. To form a lower n-type contact layer.
On the n-type contact layer, AlN was grown to a thickness of about 1.5 nm using TMA and ammonia gas at a temperature of about 950 to 1350 ° C. to form an n-side AlN layer.
Subsequently, the temperature was set again to about 900 to 1300 ° C., and GaN doped with 4.5 × 10 ¹⁸ / cm ^{3 of} Si was grown to a thickness of about 4.0 μm using TMG, ammonia gas, and silane gas. An upper n-type contact layer was formed.

(Undoped semiconductor layer)
Next, only the silane gas is stopped, the first layer made of undoped GaN is grown to a thickness of about 150 nm using TMG and ammonia gas at a temperature of about 900 to 1300 ° C., and then the silane gas is added at the same temperature. In addition, a second layer made of GaN doped with Si of 4.5 × 10 ¹⁸ / cm ³ was grown to a thickness of about 20 nm. This is repeated a total of two times. Finally, only the silane gas is stopped, and an undoped GaN layer is grown to a thickness of about 10 nm at the same temperature, and an undoped semiconductor layer having a total thickness of about 350 nm consisting of five layers. Formed.

(N-type multilayer film layer)
Next, at the same temperature, a first layer made of undoped GaN is grown to about 1.5 nm, and then the temperature is set to about 800 to 1000 ° C., and TMG, TMI, and ammonia are used to form a first layer made of undoped InGaN. Two layers were grown about 1 nm. These operations are repeated to alternately stack 20 layers, and finally a first nitride semiconductor layer made of GaN is grown by about 1.5 nm to have a superlattice structure with a total thickness of about 51.5 nm. A mold multilayer film layer was formed.

(Active layer)
After growing Si-doped GaN by about 3.5 nm using TMG, ammonia gas and silane gas at a temperature of about 900-1300 ° C., only silane gas is stopped and GaN is grown by about 1.5 nm to a thickness of about 5 nm. The barrier layer was formed.
Next, a well layer made of undoped InGaN is grown to a thickness of about 3 nm using TMG, TMI and ammonia at a temperature of about 600 to 1000 ° C., and then a barrier layer made of undoped GaN using TMG and ammonia. Was grown to a thickness of about 5 nm. In addition, nine well layers and nine barrier layers are alternately stacked in the order of well + barrier + well + barrier +... + Barrier, and an active layer consisting of a multiple quantum well structure having a total thickness of about 72 nm. A layer was formed.

(P-side cladding layer)
Next, using TMG, TMA, ammonia and Cp ₂ Mg (cyclopentadienylmagnesium) at a temperature of about 900 to 1000 ° C., p-type AlGaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is about 10 nm thick. Next, undoped GaN was grown to a thickness of about 80 nm using TMG and ammonia to form a p-side cladding layer.

(P-type GaN contact layer)
On the undoped GaN layer, p-type GaN doped with Mg at 1 × 10 ²⁰ / cm ³ is grown to a thickness of about 50 nm using TMG, ammonia, and Cp ₂ Mg at a temperature of about 900 to 1000 ° C. A p-type contact layer was formed.

  After completion of the reaction, the temperature was lowered to room temperature, and the wafer was annealed at about 300 ° C. to 700 ° C. in a nitrogen atmosphere reaction vessel to further reduce the resistance of the p-side nitride semiconductor layer.

(electrode)
Next, the wafer is taken out from the reaction container, a mask having a predetermined shape is formed on the surface of the uppermost p-type contact layer, and a depth of about 1.5 μm from the p-type contact layer side is obtained by an RIE (reactive ion etching) apparatus. Etching was then performed to expose the surface of the n-type contact layer.
Subsequently, a p-side translucent electrode made of ITO was formed on almost the entire surface of the p-type contact layer. Next, a p-side pad electrode and an n-side electrode were formed on the formed p-side translucent electrode and on the n-type contact layer exposed by etching. At this time, in this example, the distance between the n-side electrode and the n-side AlN layer was set to about 3.0 μm.

  Finally, the wafer was cut into chips to obtain light emitting elements.

[Example 2]
In the light emitting device of Example 2, after an n-type contact layer was grown by about 3.0 μm, AlN was grown by about 1.5 nm, and then an n-type contact layer was grown again by about 3.0 μm, and etching removal was performed. The same procedure as in Example 1 was performed except that the distance between the n-side electrode and the n-side AlN layer was set to about 2.0 μm.

[Example 3]
In the light emitting device of Example 3, after growing the n-type contact layer by about 4.0 μm, AlN was grown by about 1.5 nm, and then the n-type contact layer was grown again by about 2.0 μm, and then removed by etching. The same procedure as in Example 1 was performed except that the distance between the n-side electrode and the n-side AlN layer was set to about 1.0 μm.

[Example 4]
In the light emitting device of Example 4, after growing the n-type contact layer by about 5.0 μm, AlN is grown by about 1.5 nm, and then the n-type contact layer is grown again by about 1.0 μm, and then removed by etching. The same procedure as in Example 1 was performed except that the distance between the n-side electrode and the n-side AlN layer was set to about 0.1 μm.

[Example 5]
In the light-emitting device of Example 5, after growing an n-type contact layer by about 5.0 μm, AlN was grown by 2.0 nm, and an n-type contact layer was grown again by about 2.0 μm, and etching removal removed n The same procedure as in Example 1 was performed except that the distance between the side electrode and the n-side AlN layer was set to about 1.0 μm.

[Example 6]
The light-emitting element of Example 6 was manufactured in the same procedure as Example 5 except that AlN was grown by about 3.0 nm.

[Example 7]
The light-emitting element of Example 7 was manufactured in the same procedure as Example 5 except that AlN was grown to about 4.0 nm.

[Example 8]
In the light emitting device of Example 8, the thickness of the n-side AlN layer was 1.5 nm, and a p-side AlN layer having a thickness of 1.0 nm was inserted between the p-side cladding layer and the p-type contact layer. The same procedure as in Example 5 was used.

[Comparative Example 1]
In the light emitting device of Comparative Example 1 in which the n-side AlN layer is not provided between the lower n-type contact layer and the upper n-type contact layer, the source gas is used at a temperature of 900 to 1300 ° C. on the second buffer layer. Using TMG, ammonia gas and silane gas as impurity gas, GaN doped with 4.5 × 10 ¹⁸ / cm ^{3 of} Si is grown to a thickness of 7.0 μm to form an n-type contact layer, and undoped thereon It was produced by the same method as in Example 1 except that the semiconductor layer was formed.

[Comparative Example 2]
The light emitting device of Comparative Example 2 was fabricated in the same procedure as in Example 5 except that AlGaN was grown to about 5.0 nm instead of the n-side AlN layer.

[Comparative Example 3]
The light emitting device of Comparative Example 3 was fabricated in the same procedure as in Example 5 except that InGaN was grown to about 10 nm instead of the n-side AlN layer.

  Tables 1 and 2 show configurations of the light-emitting elements of Examples 1 to 8 and Comparative Examples 1 to 3.

(Relationship between n-side AlN layer insertion position and electrostatic withstand voltage characteristics)
Voltage was applied to the light emitting elements of Examples 1 to 4 and Comparative Example 1 to examine the electrostatic withstand voltage characteristics. FIG. 2 shows the breakdown rate when voltages of 50 V and 300 V are applied. The nearer the distance between the n-side electrode and the n-side AlN layer, the lower the breakdown rate, and the light-emitting elements of Examples 1 to 4 had zero breakdown rate at 50V.
In the conventional LED structure in which the n-type contact layer is exposed by etching, current flows mainly as shown in FIG. On the other hand, as the n-side AlN layer approaches the n-side electrode as in the first to fourth embodiments, current flows into the interface between the n-side AlN layer and the n-type contact layer as shown in FIG. It becomes easy. As a result, the current diffusion effect is enhanced in the present invention, and it is considered that the electrostatic withstand voltage characteristic is improved.

(Carrier mobility test)
An AlN layer having a thickness of 0 to 10 nm was grown on an undoped GaN layer having a thickness of 3 μm, and an undoped GaN layer was further grown by 30 nm thereon, so that samples having different thicknesses of AlN layers were produced. The carrier mobility of each sample thus obtained was measured by the van der Pauw method using a Hall measuring device. The results are shown in FIG.

3 that the thickness of the AlN layer is preferably 1 to 10 nm, more preferably 1 to 5 nm, and still more preferably 1 to 3 nm. However, the thickness of the AlN layer is most preferably 3 to 4 nm in consideration of the breakdown rate, breakdown voltage, the result of _Vf , etc., which will be described later.

(Relationship between thickness of n-side AlN layer and electrostatic withstand voltage characteristic)
Voltage was applied to the light emitting elements of Examples 5 and 6, and 7 and Comparative Examples 2 and 3, and the electrostatic withstand voltage characteristics were examined. FIG. 4 shows the test result of the destruction rate when a voltage of 300 V is applied. When FIG. 2 is compared with FIG. 4, the thickness of the n-side AlN layer is more than 60% in Example 4, where the thickness of the n-side AlN layer is 1.5 nm. It can be seen that the light-emitting elements of Examples 5, 6, and 7 having 2 nm, 3 nm, and 4 nm have a higher electrostatic breakdown voltage characteristic of a breakdown rate of 6.5% or less.

  In particular, the destruction rates of Examples 6 and 7 are as low as 3.3% or less. In contrast, the breakdown rates of Comparative Example 2 in which a 5.0 nm AlGaN layer was grown instead of the n-side AlN layer and Comparative Example 3 in which a 10 nm InGaN layer was grown were 7.6% and 8.5%, respectively. Met. From this, it can be seen that Examples 6 and 7 in which the n-side AlN layer is grown are more excellent in electrostatic withstand voltage characteristics than Comparative Examples 2 and 3 in which AlGaN and InGaN are grown.

It was measured forward voltage V _f at 20mA of a light-emitting element of Examples 6 and 7, and Comparative Example 1. The results are shown in FIG. Even when the thickness of the n-side AlN layer was increased to 4 nm (Example 7), the forward voltage remained at the same level as in Comparative Example 1 in which the n-side AlN layer was not inserted.

The thickness of the n-side AlN layer is preferably 1 to 3 nm as described above when only the carrier mobility test is taken into consideration, but from FIG. 4, it plays a role as a current diffusion layer for improving the electrostatic withstand voltage characteristics. Considering it, it can be said that a film thickness of 3 to 4 nm is preferable. Further, as shown in FIG. 5, even when the film thickness of the n-side AlN layer is 3 to 4 nm, the value of _Vf remains about the same as that of the light emitting element in which the n-side AlN layer is not inserted.

  The n-side AlN layer is inserted between the upper n-type contact layer and the lower n-type contact layer, and the p-side AlN layer is further inserted between the p-side cladding layer and the p-type contact layer. With respect to the light emitting element, the destruction rate was measured. The results are shown in Table 3. The light emitting device of Example 8 in which the p-side AlN layer was inserted had a reduced breakdown rate at 300 V and a very low breakdown rate at 500 V compared to the light emitting devices of Examples 1 to 7, and the electrostatic The breakdown voltage characteristics have been greatly improved.

  In the light emitting device according to the present invention, the relatively crystalline brittle active layer is protected, and the electrostatic withstand voltage characteristic can be improved.

1 substrate 2 n-type contact layer 2a lower n-type contact layer 2b upper n-type contact layer 3 active layer 4 p-side nitride semiconductor layer 5 p-side electrode 5a p-side translucent electrode 5b p-side pad electrode 6 n-side electrode 7 n-side AlN layer

Claims (7)

An n-side nitride semiconductor layer, an active layer, and a p-side nitride semiconductor layer are sequentially stacked on the substrate,
In a light emitting device in which an n-side electrode and a p-side electrode are provided on the n-side nitride semiconductor layer and the p-side nitride semiconductor layer, respectively.
The n-side nitride semiconductor layer has an n-type contact layer composed of an upper n-type contact layer and a lower n-type contact layer in contact with the n-type electrode;
Between the upper n-type contact layer and the lower n-type contact layer, an AlN layer having a composition different from that of the upper n-type contact layer and the lower n-type contact layer is provided.
The light emitting device, wherein a distance between the AlN layer and the n-side electrode is shorter than a distance between the AlN layer and the substrate.   The light emitting device according to claim 1, wherein a distance between the AlN layer and the n-side electrode is shorter than a thickness of the lower n-type contact layer.   The light emitting element of Claim 1 or 2 whose distance between the said AlN layer and the said n side electrode is 0.1 micrometer-3.0 micrometers.   The light emitting element of any one of Claims 1-3 whose thickness of the said AlN layer is 1 nm-10 nm.   The light emitting element of any one of Claims 1-3 whose thickness of the said AlN layer is 3 nm-4 nm.   The light emitting device according to claim 1, wherein the upper n-type contact layer and the lower n-type contact layer are GaN layers. p-side nitride semiconductor layer has a p-type contact layer, and a different AlN layer in composition and the p-type contact layer, different AlN layer in composition and the p-type contact layer, the p-type contact layer and the active characterized in that provided in contact with the p-type contact layer between the layer, the light emitting device according to any one of claims 1-6.

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