JP3890930B2 - Nitride semiconductor light emitting device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention consists of a light emitting diode (LED), a nitride semiconductor used in the laser diode (LD), etc. _{(In a Al b Ga 1-} a-b N, 0 ≦ a, 0 ≦ b, a + b ≦ 1) light emitting In particular, the present invention relates to a double heterostructure nitride semiconductor light emitting device having an active layer between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer.
[0002]
[Prior art]
Nitride semiconductors (In _a Al _b Ga _1-ab N, 0 ≦ a, 0 ≦ b, a + b ≦ 1) are known as materials for light-emitting elements such as LEDs and LDs that emit ultraviolet to red light. Using this semiconductor material, we announced a blue LED with a luminous intensity of 1 cd in November 1993, a blue-green LED with a luminous intensity of 2 cd in April 1994, and a blue LED with a luminous intensity of 2 cd in October 1994. Announced. All of these LEDs have been commercialized and are now in practical use such as displays and road signals.
[0003]
FIG. 2 shows the structure of a conventional blue and blue-green LED light-emitting chip made of a nitride semiconductor. Basically, on the substrate 21, a buffer layer 22 made of GaN, an n-type contact layer 23 made of n-type GaN, an n-type cladding layer 24 made of n-type AlGaN, and an active layer 25 made of n-type InGaN. And a p-type cladding layer 26 made of p-type AlGaN and a p-type contact layer 27 made of p-type GaN in this order. The n-type InGaN of the active layer 25 is doped with donor impurities such as Si and Ge and / or acceptor impurities such as Zn and Mg, and the emission wavelength of the LED element changes the In composition ratio of InGaN of the active layer By changing the kind of impurities doped in the active layer, it is possible to change from ultraviolet to red. Currently, LEDs having an emission wavelength of 510 nm or less in which an active layer is doped with a donor impurity and an acceptor impurity at the same time have been put into practical use.
[0004]
[Problems to be solved by the invention]
A conventional blue LED has a forward current (If) of 20 mA, a forward voltage (Vf) of 3.6 V to 3.8 V, a light emission output of nearly 3 mW, and a light emission output more than 20 times that of a blue LED made of SiC. have. The forward voltage is low because a pn junction is formed, and the light emission output is high because a double hetero structure is realized. Thus, although LEDs currently in practical use have very high performance, light emitting elements such as LEDs and LDs with higher performance are demanded. For example, the Vf of the LED achieves a low value of 3.6 V to 3.8 V as described above. However, in order to realize a light emitting element with a small electrode width and electrode area like the LD, the Vf is further reduced. It is necessary to let
[0005]
Accordingly, the present invention has been made in view of such circumstances, and an object of the present invention is to further improve the performance of a light-emitting element made of a nitride semiconductor having a double hetero structure. The object of the present invention is to provide an element having excellent luminous efficiency by further reducing the Vf of the light emitting element.
[0006]
[Means for Solving the Problems]
The present invention provides a double heterostructure nitridation having an active layer that emits light between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer, and a positive electrode formed on the surface of the p-type nitride semiconductor layer. In the semiconductor light emitting device, the active layer may be a single quantum well structure having only a well layer made of In _x Ga _1-x N (0 < X <1) , or In _x Ga _1-x N (0 < X ≦ 1) an active layer containing In having a multiple quantum well structure including a well layer made of 1) and a barrier layer made of In _Y Ga _1-Y N (0 ≦ Y <1, Y <X), and the p-type nitride semiconductor The layers are, in order from the side in contact with the positive electrode, a first p-type nitride semiconductor layer having a higher acceptor impurity concentration and a second p-type nitride having a lower acceptor impurity concentration than the first p-type nitride semiconductor layer. Semiconductor layer and p selected for composition of GaN, AlGaN or InAlGaN And a cladding layer, wherein the thickness of the first p-type nitride semiconductor layer is 500Å or less.
[0007]
Further, in the light emitting element, the thickness of the first p-type nitride semiconductor is adjusted to 0.1 μm or less, more preferably 500 angstroms or less, and most preferably 200 angstroms or less. If it is thicker than 0.1 μm, crystal defects due to impurities increase in the crystal itself, and Vf tends to increase.
[0008]
[Action]
p layer of high carrier concentration of ^{p +} -type and p-type and technology of low carrier concentration JP 6-151964, JP-A-6-151965, disclosed in JP-A 6-151966 Patent like. The light emitting devices disclosed in these publications emit light by homojunction of GaN. Therefore, with reference to the pn junction interface, the n-type GaN layer is made n-type with a low carrier concentration and n + -type with a high carrier concentration in a direction away from the junction interface, and p-type GaN is made p-type with a low carrier concentration. P + type with high carrier concentration. By combining the n layer and the p layer having these two-stage carrier concentrations, the long life of the light emitting element and the light emission luminance are improved.
[0009]
On the other hand, the light-emitting element of the present invention differs from the above publication in that the p-type layer of the light-emitting element having a double hetero structure is composed of a second p-type layer having a low acceptor impurity concentration and a first p-type having a high acceptor impurity concentration. It is the point which is made into a layer. A light emitting element having a double hetero structure has a light emission output that is 10 times higher than that of a homojunction light emitting element. Therefore, even if the p-type layer is a combination of the p + type and the p type as in the above publication, there is almost no increase in output. Rather, the present invention is different from the conventional technique in that the Vf of the double hetero structure is lowered and the luminous efficiency is improved rather than the luminous output. Regarding the acceptor impurity, the carrier concentration is generally proportional to the acceptor impurity concentration. However, in the case of a nitride semiconductor, the semiconductor layer is doped with the acceptor impurity and then annealed at 400 ° C. or higher to complete p Acts as a mold. For this reason, the hole carrier concentration often varies depending on the annealing state, annealing temperature, etc., and it is difficult to measure the exact carrier concentration when the device structure is used. Therefore, in the present invention, the light emitting device is characterized by the acceptor impurity concentration. It is attached.
[0010]
Next, the light emitting device of the present invention is not based on the pn junction interface as in the prior art, but the contact surface of the positive electrode is used as a reference, and the surface in contact with the positive electrode is the first p having a high impurity concentration. The difference is that the second p-type layer has a low impurity concentration in contact with the first p-type layer. By configuring the p layer with reference to the layer in contact with the positive electrode, Vf can be lowered.
[0011]
Furthermore, the most different point between the light emitting element disclosed in the publication and the light emitting element of the present invention is the thickness of the p + layer. That is, in the above publication, the light emission output of the light emitting element is lowered unless the film thickness of the p + type semiconductor layer having a high carrier concentration is 0.2 μm or more. However, in the light emitting element of the present invention, the first p type having a high impurity concentration is reduced. When the film thickness of the layer is 0.2 μm or more, Vf increases. This is due to deterioration of crystallinity due to impurity doping. Conversely, in the light emitting device of the present invention, the thickness of the first p-type layer having a high impurity concentration is preferably 0.1 μm or less. By setting the thickness to 0.1 μm or less, Vf of the light emitting element can be effectively reduced.
[0012]
【Example】
[Example 1]
Hereinafter, the light emitting device of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the structure of a light emitting device according to an embodiment of the present invention. The light emitting device includes a buffer layer 2, an n-type contact layer 3, an n-type cladding layer 4, an active layer 5, a p-type cladding layer 6, a second p-type contact layer 72 having a low acceptor impurity concentration, and an acceptor. A structure in which first p-type contact layers 71 having a high impurity concentration are sequentially stacked is shown. Further, a positive electrode 9 is formed on the first p-type contact layer 71, and a negative electrode 8 is formed on the n-type contact layer 3.
[0013]
In addition to sapphire (including A-plane, C-plane, and R-plane), the substrate 1 includes a substrate that is lattice-mismatched with a nitride semiconductor such as SiC (including 6H and 4H), ZnO, Si, and GaAs, and NGO ( A substrate having a lattice constant close to that of a nitride semiconductor made of an oxide single crystal such as (neodymium gallium oxide) can be used.
[0014]
The buffer layer 2 is preferably grown by growing GaN, AlN, GaAlN or the like at a film thickness of, for example, 50 Å to 0.1 μm. For example, the buffer layer 2 can be formed by growing at a low temperature of 400 ° C. to 600 ° C. according to the MOVPE method. The buffer layer 2 is provided to alleviate the lattice mismatch between the substrate 1 and the nitride semiconductor, but a substrate having a lattice constant close to that of a nitride semiconductor such as SiC or ZnO, or a substrate lattice-matched to the nitride semiconductor is used. In doing so, the buffer layer may not be formed.
[0015]
The n-type contact layer 3 is a layer for forming the negative electrode 8, and it is preferable to grow GaN, AlGaN, InAlGaN or the like with a film thickness of, for example, 1 μm to 10 μm. Among them, the material of the negative electrode can be selected by selecting GaN. A preferred ohmic contact can be obtained. As the material of the negative electrode 8, for example, Ti and Al, Ti and Au, or the like can be preferably used.
[0016]
The n-type cladding layer 4 is preferably grown from GaN, AlGaN, InAlGaN or the like with a film thickness of, for example, 500 angstroms to 0.5 μm. Among them, a layer with good crystallinity can be obtained by selecting GaN or AlGaN. Further, either the n-type cladding layer 4 or the n-type contact layer 3 can be omitted. If either one is omitted, the remaining layers act as an n-type cladding layer and an n-type contact layer.
[0017]
The active layer 5 may be a nitride semiconductor such as InGaN, InAlGaN, or AlGaN having a band gap energy smaller than that of the cladding layer, and is preferably InGaN in which the composition ratio of indium is appropriately changed depending on the desired band gap. The active layer 5 may have a multiple quantum well structure in which, for example, a combination of InGaN / GaN, InGaN / InGaN (having different compositions), and the like, and respective thin films are stacked. In any active layer of single quantum well structure or multiple quantum well structure, the active layer may be either n-type or p-type. In particular, non-doped (non-added) narrow band-to-band emission and excitons. Light emission or quantum well level light emission is obtained, which is particularly preferable for realizing an LED element or an LD element. When the active layer has a single quantum well (SQW) structure or a multi quantum well (MQW) structure, a light-emitting element having a very high output can be obtained. SQW and MQW indicate the structure of an active layer that can emit light between quantum levels of non-doped InGaN. For example, in SQW, the active layer is made of In _X Ga _1-X N (0 ≦ X <1) having a single composition. When the film thickness of the In _X Ga _1-X N is 100 angstroms or less, more preferably 70 angstroms or less, strong light emission between quantum levels can be obtained. MQW is a multilayer film in which a plurality of thin films of In _X Ga _1-X N (including X = 0 and X = 1 in this case) having different composition ratios are stacked. In this way, by setting the active layer to SQW and MQW, light emission of about 365 nm to 660 nm can be obtained by light emission between quantum levels. As described above, the thickness of the quantum well layer is preferably 70 angstroms or less. In the multiple quantum well structure, it is desirable that the well layer is composed of In _X Ga _1-X N, and the barrier layer is also composed of In _Y Ga _1-Y N (Y <X, including Y = 0 in this case). Particularly preferably, when the well layer and the barrier layer are formed of InGaN, the active layer having good crystallinity can be obtained because it can be grown at the same temperature. When the thickness of the barrier layer is 150 angstroms or less, more preferably 120 angstroms or less, a light-emitting element with high output can be obtained. Further, the active layer 5 may be doped with donor impurities and / or acceptor impurities. If the crystallinity of the active layer doped with impurities is the same as that of non-doped, doping with donor impurities can further increase the emission intensity between bands as compared with non-doped ones. When the acceptor impurity is doped, the peak wavelength can be brought to the lower energy side by about 0.5 eV than the peak wavelength of the interband light emission, but the half width is widened. When the acceptor impurity and the donor impurity are doped at the same time, the emission intensity of the active layer doped with only the acceptor impurity can be further increased. In particular, when realizing an active layer doped with an acceptor impurity, the conductivity type of the active layer is preferably n-type by simultaneously doping a donor impurity such as Si. The active layer 5 can be grown with a film thickness of, for example, several angstroms to 0.5 μm. However, when the active layer has a single quantum well structure or a multiple quantum well structure and the thickness of the nitride semiconductor layer constituting the active layer is reduced, In is included between the n-type cladding layer 4 and the active layer 5. It is desirable to form the second n-type cladding layer 40 made of an n-type nitride semiconductor.
[0018]
The p-type cladding layer 6 is preferably grown from GaN, AlGaN, InAlGaN or the like with a film thickness of, for example, 500 Å to 0.5 μm. Among them, a layer with good crystallinity can be obtained by selecting GaN or AlGaN. The p-type cladding layer 6 can be omitted.
[0019]
Next, the contact layers 71 and 72 that characterize the present invention will be described. The contact layers 71 and 72 form the positive electrode 9 and obtain a preferable ohmic contact with the positive electrode 9. The closer to the complete ohmic, the lower the Vf of the light emitting element. Therefore, this contact layer is composed of a first p-type contact layer 71 which is a first nitride semiconductor layer having a high acceptor impurity concentration in the layer in contact with the positive electrode 9, and acceptor impurities than the first p-type contact layer. The second p-type contact layer 72 is a second nitride semiconductor having a low concentration.
[0020]
The first p-type contact layer 71 and the second p-type contact layer 72 are preferably formed of a nitride semiconductor having the same composition, and for example, GaN, AlGaN, InAlGaN or the like can be grown. Among them, by selecting GaN, preferable ohmic contact with the material of the positive electrode 9 can be obtained.
[0021]
The acceptor impurity concentration of the high concentration first p-type contact layer 71 is desirably adjusted to 1 × 10 ^{17 to} 5 × 10 ²¹ / cm ³ . If it is lower than 1 × 10 ¹⁷ / cm ³ , it is difficult to obtain ohmic contact with the electrode, and if it is higher than 5 × 10 ²¹ / cm ³ , the crystallinity of the nitride semiconductor tends to deteriorate due to impurities, and Vf tends to increase. It is in.
[0022]
On the other hand, the acceptor impurity concentration of the low-concentration second p-type contact layer 72 is desirably adjusted to a range of 2 × 10 ^{15 to} 5 × 10 ²⁰ / cm ³ . When it is lower than 2 × 10 ¹⁵ / cm ³ , the resistance as a p-type is increased, so that Vf tends to increase. If it is higher than 5 × 10 ²⁰ / cm ^3, it is difficult to achieve a balance with the high-concentration first p-type contact layer 71, and Vf tends to be hardly improved.
[0023]
As described above, the hole carrier concentration of the contact layers 71 and 72 is changed by changing the concentration of the acceptor impurity doped in the nitride semiconductor, or the contact layers 71 and 72 doped with the acceptor impurity at 400 ° C. or higher. Although it can be adjusted by annealing, it is difficult to measure an accurate value. As an approximate value, the first p-type contact layer 71 having, for example, a hole carrier concentration of about 1 × 10 ^{16 to} 5 × 10 ¹⁹ / cm ³ is obtained by annealing at 400 ° C. or more with the acceptor impurity concentration. Similarly, the second p-type contact layer 72 having a hole carrier concentration of about 1 × 10 ¹⁵ to 1 × 10 ¹⁹ / cm ³ is obtained.
[0024]
As a material of the positive electrode 9 from which the first p-type contact layer 71 and a preferable ohmic can be obtained, a metal containing Ni and Au can be used. A positive electrode containing Ni and Au can obtain a preferable ohmic particularly with p-type GaN.
[0025]
Light-emitting element of the present invention are, for example MOVPE (metal organic vapor phase epitaxy), MBE (molecular beam vapor deposition), HDVPE by a vapor deposition method (hydride vapor phase epitaxy) or the like, an In _a on a substrate It is obtained by stacking Al _b Ga _1-ab N (0 ≦ a, 0 ≦ b, a + b ≦ 1) with a conductivity type such as n-type or p-type. Although an n-type nitride semiconductor can be obtained in a non-doped state, it can be obtained by introducing donor impurities such as Si, Ge, and S into the semiconductor layer during crystal growth.
[0026]
On the other hand, the p-type nitride semiconductor layer can be obtained by introducing acceptor impurities such as Mg, Zn, Cd, Ca, Be, and C into the semiconductor layer during crystal growth as well. More preferable p-type can be obtained by annealing at 400 ° C. or higher after introduction of acceptor impurities.
[0027]
Next, the light-emitting element of FIG. 1 will be specifically described. The following examples show growth methods by the MOVPE method.
[0028]
First, using TMG (trimethylgallium) and NH ₃ , a buffer layer 2 made of GaN is grown to a thickness of 500 angstroms at 500 ° C. on the C surface of the sapphire substrate 1 set in the reaction vessel.
[0029]
Next, the temperature is raised to 1050 ° C., and an n-type contact layer 23 made of Si-doped n-type GaN is grown to a thickness of 4 μm using silane gas in addition to TMG and NH ₃ .
[0030]
Subsequently, TMA (trimethylaluminum) is added to the source gas, and an n-type cladding layer 4 made of Si-doped n-type Al _0.3 Ga _0.7 n phase is grown at a thickness of 0.1 μm at 1050 ° C.
[0031]
Next, the temperature is lowered to 800 ° C., and TMG, TMI (trimethylindium), NH 3, silane gas, and DEZ (diethyl zinc) are used, and the active layer 5 made of Si + Zn doped n-type In _0.05 Ga _0.95 N is reduced to 0.00. Growing with a film thickness of 1 μm.
[0032]
Next, the temperature is raised to 1050 ° C., TMG, TMA, NH ₃ , Cp ₂ Mg (cyclopentadienyl magnesium) is used, and the p-type cladding layer 6 made of Mg-doped p-type Al _0.3 Ga _0.7 N is formed. The film is grown to a thickness of 0.1 μm.
[0033]
Next, a second p-type contact layer 72 made of Mg-doped p-type GaN is grown to a thickness of 0.5 μm using TMG, NH ₃ , and Cp ₂ Mg at 1050 ° C. The Mg concentration of the second p-type contact layer was 1 × 10 ¹⁸ / cm ³ .
[0034]
Subsequently, the flow rate of Cp ₂ Mg is increased at 1050 ° C., and the first p-type contact layer 71 made of Mg-doped p-type GaN is grown to a thickness of 200 Å. The Mg concentration of the first p-type contact layer 71 was 2 × 10 ¹⁹ / cm ³ .
[0035]
After completion of the reaction, the temperature is lowered to room temperature, the wafer is taken out of the reaction vessel, and the wafer is annealed at 700 ° C. to further reduce the resistance of the p-type layer. Next, a mask having a predetermined shape is formed on the surface of the uppermost p-type contact layer 7 and etching is performed until the surface of the n-type contact layer 3 is exposed. After the etching, a negative electrode 8 made of Ti and Al is formed on the surface of the n-type contact layer 3, and a positive electrode 9 made of Ni and Au is formed on the surface of the first p-type contact layer 71. After the electrodes were formed, the wafer was separated into 350 μm square chips to obtain LED elements. This LED element had If20 mA, Vf 3.1 V, emission peak wavelength 450 nm, half-value width 70 nm, blue emission, and emission output 3 mW.
[0036]
[Example 2]
A light emitting device was obtained in the same manner as in Example 1 except that the film thickness of the first p-type contact layer 71 was changed to 500 angstroms. As a result, at If20 mA, Vf was 3.2 V and the light emission output was almost the same.
[0037]
[Example 3]
A light emitting device was obtained in the same manner as in Example 1 except that the film thickness of the first p-type contact layer 71 was set to 0.1 μm. At If mA, Vf was 3.3 V and the light emission output was 2.9 mW. .
[0038]
[Example 4]
A light emitting device was obtained in the same manner as in Example 1 except that the thickness of the first p-type contact layer 71 was set to 0.3 μm. At If mA, Vf was 3.7 V, and the light emission output was 2.8 mW. It was.
[0039]
[Example 5]
In Example 1, except that the Mg concentration of the second p-type contact layer 72 is 5 × 10 ¹⁷ / cm ³ and the Mg concentration of the first p-type contact layer 71 is 1 × 10 ¹⁹ / cm ³ , When an LED element was obtained in the same manner, it showed almost the same characteristics as Example 1.
[0040]
[Example 6]
FIG. 3 is a schematic cross-sectional view showing the structure of the light-emitting element according to Example 5. This light-emitting element is different from the light-emitting element of FIG. 1 in that a second n-type cladding layer made of an n-type nitride semiconductor containing In as a new buffer layer between the n-type cladding layer 4 and the active layer 5. 40 is being formed. The second cladding layer 40 is preferably formed with a film thickness of 10 angstroms or more and 0.1 μm or less. Further, when the film thicknesses of the second n-type cladding layer 40 and the active layer 5 are 300 angstroms or more, In The first n-type clad layer 40 containing In and the active layer 5 containing In act as a buffer layer, and the n-type clad layer 4 and the p-type clad layer 6 can be grown with good crystallinity without cracks. Further, by growing the second n-type cladding layer 40, an active layer having a quantum structure that is not doped with impurities can be realized, and the half-value width is narrow and light emission with high output can be obtained. The second n-type cladding layer 40 may be GaN.
[0041]
The second n-type cladding layer 40 functions as a buffer layer between the active layer 5 and the n-type cladding layer 4 containing Al and Ga. That is, since the second n-type cladding layer 40 containing In and Ga has a soft nature as a crystal property, the lattice constant irregularity between the n-type cladding layer 4 containing Al and Ga and the active layer 5 is reduced. It works to absorb strain caused by the difference in thermal expansion coefficient. Therefore, even if the active layer has a single quantum well structure or a multiple quantum well structure and the nitride semiconductor layer constituting the active layer is made thin, the active layer 5 and the n-type cladding layer 4 are not cracked. The active layer is elastically deformed, and crystal defects in the active layer are reduced. That is, by making the active layer a quantum well structure, the crystallinity of the active layer is improved, so that the light emission output is increased. Furthermore, when the active layer has a quantum well structure, the light emission output increases due to the quantum effect and the exciton effect. In other words, in the conventional light emitting device, the thickness of the active layer is increased to, for example, 1000 angstroms or more to prevent cracks in the cladding layer and the active layer. However, the active layer always has a difference in thermal expansion coefficient and distortion due to lattice irregularity. In the conventional light emitting device, the thickness of the active layer exceeds the critical thickness that can be elastically deformed. It cannot be deformed, causes many crystal defects in the active layer, and does not emit much light by interband light emission. By forming the second n-type cladding layer 40, it is possible to dramatically improve the light emission output of the light emitting element when the active layer has a quantum structure.
[0042]
Specifically, after growing the n-type cladding layer 4 in Example 1, the temperature is lowered to 800 ° C., and TMG, TMI (trimethylindium), NH ³ , and silane gas are used, and Si-doped n-type In _0.01 A second n-type cladding layer 40 made of Ga _0.99 N is grown to a thickness of 500 angstroms.
[0043]
Subsequently, an active layer 5 made of non-doped n-type In _0.05 Ga _0.95 N is grown to a thickness of 80 Å at 800 ° C. using TMG, TMI, and NH ₃ . Thereafter, in the same manner as in Example 1, the p-type cladding layer 6, the second p-type contact layer 72, and the first p-type contact layer 71 were grown to form an LED element. This LED element had an If of 20 mA. Blue light emission of Vf 3.1 V, emission peak wavelength of 400 nm was exhibited, and the light emission output was 12 mW. Further, the half-value width of the emission spectrum was 20 nm, and light emission with very good color purity was exhibited.
[0044]
[Example 7]
In Example 6, the composition of the active layer 5 is 25 Å for the well layer made of non-doped In _0.05 Ga _0.95 N and 50 Å for the barrier layer made of non-doped In _0.01 Ga _0.99 N. Grow in. This operation was repeated 26 times. Finally, a well layer was stacked to grow an active layer 6 having a total thickness of about 2000 angstroms. Thereafter, an LED element was formed in the same manner as in Example 6. This LED element also showed blue light emission with Vf of 3.1 V and emission peak wavelength of 400 nm at If20 mA, and the light emission output was 12 mW. Further, the half-value width of the emission spectrum was 20 nm, and light emission with very good color purity was exhibited.
[0045]
【The invention's effect】
As described above, the light-emitting element of the present invention is a double-heterostructure light-emitting element in which the p-type layer forming the positive electrode is divided into the first p-type layer having a high acceptor impurity concentration and the second p-type layer having a low impurity concentration. By using a p-type layer, Vf can be lowered, so that the light emission efficiency is improved. Therefore, when realizing a large display, an outdoor advertising board, etc. using a large amount of LEDs, a device with low power consumption can be realized, and its industrial utility value is great.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing a structure of a light-emitting element according to an embodiment of the present invention.
FIG. 2 is a schematic cross-sectional view showing the structure of a conventional light emitting element.
FIG. 3 is a schematic cross-sectional view showing the structure of a light emitting device according to another embodiment of the present invention.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... substrate 2 ... buffer layer 3 ... n-type contact layer 4 ... n-type cladding layer 5 ... active layer 6 ... p-type cladding layer 72 ... .... Second p-type contact layer 71 ... First p-type contact layer 8 ... Negative electrode 9 ... Positive electrode

Claims (6)

A nitride semiconductor light emitting device having a double hetero structure having an active layer that emits light between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer and having a positive electrode formed on the surface of the p-type nitride semiconductor layer In
The active layer is a single quantum well structure having only a well layer made of In _x Ga _1-x N (0 < X <1) , or a well layer made of In _x Ga _1-x N (0 < X ≦ 1). And an active layer containing In having a multiple quantum well structure with a barrier layer made of In _Y Ga _1-Y N (0 ≦ Y <1, Y <X),
The p-type nitride semiconductor layer has a first p-type nitride semiconductor layer having a higher acceptor impurity concentration and a lower acceptor impurity concentration than the first p-type nitride semiconductor layer in order from the side in contact with the positive electrode. Two p-type nitride semiconductor layers, and a p-type cladding layer selected from a composition of GaN, AlGaN or InAlGaN,
The nitride semiconductor light-emitting element, wherein the first p-type nitride semiconductor layer has a thickness of 500 mm or less .   The nitride semiconductor light emitting device according to claim 1, wherein the p-type cladding layer is made of AlGaN as a composition.   3. The nitride semiconductor light emitting device according to claim 1, wherein the n-type nitride semiconductor layer has an n-type cladding layer selected from GaN, AlGaN, or InAlGaN as a composition. 4. 4. The nitride semiconductor light emitting device according to claim 3, wherein a second n-type cladding layer made of an n-type nitride semiconductor containing In is formed between the n-type cladding layer and the active layer. element. The positive electrode is, the nitride semiconductor light-emitting device according to any one of claims 1 to 4, characterized in that it comprises nickel and gold. The acceptor impurity of the first p-type nitride semiconductor layer is Mg having a concentration of 1 × 10 ^{17 to} 5 × 10 ²¹ / cm ³ , and the acceptor impurity of the second p-type nitride semiconductor layer is 2 × 10 ^{15 ~5} × ¹⁰ 20 / cm ³ density of the nitride semiconductor light-emitting device according to any one of claims 1 to 5 is Mg.

Images