JP3868136B2 - Gallium nitride compound semiconductor light emitting device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention comprises a nitride semiconductor In _x Al _y Ga _1-xy N (0 ≦ x, 0 ≦ y, x + y ≦ 1), and is used for a light emitting element such as a light emitting diode element and a laser diode element. The present invention relates to a light emitting element.
[0002]
[Prior art]
Nitride semiconductors have already been put to practical use in various light sources such as full-color LED displays, traffic signal lights, and image scanner light sources as high-luminance pure green light-emitting LEDs and blue LEDs. These LED elements basically include an n-type contact layer made of GaN on a sapphire substrate, an active layer including an InGaN layer having a single quantum well structure or a multiple quantum well structure, and a p-type made of Mg-doped AlGaN. It has a structure in which a clad layer and a p-type contact layer made of Mg-doped GaN are stacked in order, and if the active layer is a single quantum well structure with a blue LED of 20 mA and an emission wavelength of 450 nm, 2.5 mW The external quantum efficiency is 5%, the active layer has a multiple quantum well structure, 5 mW, the external quantum efficiency is 9.1%, and the green light emission wavelength is 520 nm, and the single quantum well structure is 2.2 mW. In the case of an efficiency of 4.3 percent, a multiple quantum well structure, 3 mW and an external quantum efficiency of 6.3 percent exhibit very excellent characteristics.
[0003]
[Problems to be solved by the invention]
However, in recent years, the conventional nitride semiconductor element has been used for outdoor large-sized displays and the like, and further improvement in light emission output is required in consideration of application to various application products in the future. If the n-type contact layer is GaN doped with an n-type impurity as a method for increasing the light output, an element having a low resistance structure can be obtained. However, when the doping amount of the n-type impurity is increased, the crystallinity of the n-type contact layer is deteriorated. If the crystallinity of the n-type contact layer is deteriorated, the crystallinity of all the active layer, p-type cladding layer and p-type contact layer laminated thereon is also deteriorated, and the light emission output is increased. The effect will be countered.
[0004]
[Means for Solving the Problems]
Therefore, in the present invention, an n-type contact layer made of GaN doped with an n-type impurity, an active layer containing In and Ga and having a quantum well, and a p-type cladding containing p-type AlGaN doped with a p-type impurity. In a nitride semiconductor device having a layer and a p-type contact layer made of GaN doped with a p-type impurity in order, the film thickness is 10 angstroms between the n-type contact layer and the active layer and in contact with the active layer To 0.2 μm of undoped first nitride semiconductor layer is formed, and further, between the p-type cladding layer and the active layer, is in contact with the p-type cladding layer and the active layer and has a thickness of 10 Å a second nitride semiconductor layer of undoped made of AlGaN is formed is 100 Å, the p-type cladding layer of Mg doped _Al b Ga Characterized in that a layer consisting of a superlattice of _{-b N (0 <b <1} ) and Mg-doped _{In c Ga 1-c N (} 0 ≦ c <1).
[0010]
The light-emitting element of the present invention is, for example, a nitride semiconductor having a low resistance structure in which an n-type contact layer is doped with a high-concentration impurity having a Si concentration of 1 × 10 ¹⁸ / cm ³ or more. In addition, undoped In _g Al _h Ga _1-gh N (0 ≦ g, 0 ≦ h, g + h ≦ 1) is formed with a thickness of 0.2 μm or less, and is further in contact with the active layer on the p side. By forming In _i Al _j Ga _1-ij N (0 ≦ i, 0 ≦ j, i + j ≦ 1) with a film thickness of 100 angstroms or less, an element with high light emission output and good crystallinity can be obtained. . Furthermore, the p-type cladding layer has a superlattice structure of Mg-doped Al _b Ga _1-b N (0 ≦ b <1) and Mg-doped In _c Ga _1-c N (0 ≦ c <1). High light output can be maintained. Further, the larger the film thickness of the first and second nitride semiconductors, the better the crystallinity of the layer formed thereon, but if it is too thick, the carrier injection efficiency will deteriorate, It stops emitting light. Therefore, by reducing the thickness of the first nitride semiconductor on the n side to 0.2 μm or less and the thickness of the second nitride semiconductor on the p side to 100 angstroms or less, the n-type impurity is added to the n-type contact layer. As a result, even if Si is highly doped to 1 × 10 ²¹ / cm ³ , an LED element can be maintained that maintains 2.5 mW at 20 mA.
[0011]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to FIG. 1 which is a schematic cross-sectional view of a nitride semiconductor device showing the structure of a nitride semiconductor device according to an embodiment of the present invention.
FIG. 1 shows a substrate 1, a buffer layer 2, an undoped GaN layer 3, an n-type contact layer 4 containing an n-type impurity, an undoped first nitride semiconductor layer 5, and an active layer 6 having a single quantum well structure. , A second nitride semiconductor layer 7 made of undoped, a p-type cladding layer 8 containing a p-type impurity, and a p-type contact layer 9 containing a p-type impurity are sequentially stacked. Further, an n-electrode 10 is formed on the n-type cladding layer 4, and a p-electrode 11 is formed on the p-type contact layer 9.
[0012]
In the present invention, as the substrate 1, in addition to sapphire whose main surface is the sapphire C-plane, R-plane or A-plane, other insulating substrates such as spinel (MgAl ₂ O ₄ ), SiC (6H, 4H, 3C Semiconductor substrates such as Si, ZnO, GaAs, and GaN can be used.
[0013]
In the present invention, the buffer layer 2 is a nitride semiconductor made of AlGaN, and the crystallinity improvement becomes more remarkable as the composition having a smaller Al ratio, more preferably, the buffer layer 2 made of GaN.
[0014]
Next, in the present invention, the undoped GaN layer 3 is a layer formed without adding an n-type impurity during growth. When the undoped GaN layer 3 is grown on the buffer layer 2, the crystallinity of the undoped GaN layer is improved, and the crystallinity of the n-type contact layer 4 grown on the undoped GaN layer 3 is also improved.
[0015]
Next, in the present invention, the n-type contact layer 4 containing an n-type impurity is made of GaN doped with Si as an n-type impurity, and the impurity concentration is 1 × 10 ¹⁸ / cm ³ or more, 1 × 10 ²¹ / cm ³ or less, Preferably, it is adjusted to 5 × 10 ¹⁸ / cm ³ or more and 5 × 10 ²⁰ / cm ³ or less. Thus, if a large amount of n-type impurity is doped and this layer is an n-type contact layer, V _f and the threshold can be lowered. When the impurity concentration deviates from the above range, V _f tends to be difficult to decrease. Further, when the n-type contact layer 4 is formed on undoped GaN 3 having good crystallinity, the crystallinity can be improved despite having a high concentration of n-type impurities.
[0016]
The composition of the n-type contact layer 4 can be composed of In _k Al _m Ga _1-km N (0 ≦ k, 0 ≦ m, k + m ≦ 1), and the composition is not particularly limited, When GaN is Al _m Ga _1-m N having an m value of 0.2 or less, a nitride semiconductor layer with low crystallinity is easily obtained.
[0017]
Next, in the present invention, the n-side first nitride semiconductor layer 5 is undoped In _g Al _h Ga _1-gh N (0 ≦ g, 0 ≦ h, g + h ≦ 1). It is formed in contact with the active layer in the range of 0.5 μm, preferably in the range of 10 Å to 0.2 μm. Although there is a high carrier concentration on the n side, the carrier injection efficiency deteriorates when the film thickness of the first nitride semiconductor layer exceeds 0.5 μm, and a sufficient light emission output is obtained. Absent. On the other hand, if the thickness is smaller than 10 angstroms, the crystallinity of the layer formed thereon deteriorates, and a sufficient light output cannot be obtained.
[0018]
In the present invention, the active layer 6 desirably has a single or multiple quantum well structure having a well layer made of an undoped nitride semiconductor containing In and Ga, preferably InGaN. The nitride semiconductor light emitting device having a low resistance structure according to the present invention has a remarkable effect particularly in a single quantum well structure.
[0019]
Next, in the present invention, the second nitride semiconductor layer 7 on the p side is undoped In _i Al _j Ga _1-ij N (0 ≦ i, 0 ≦ j, i + j ≦ 1), from 10 angstroms, It is formed in contact with the active layer in the range of 0.1 μm, preferably in the range of 10 Å to 100 Å.
[0020]
Next, in the present invention, the p-type cladding layer 8 may be a layer composed of a single layer of Al _b Ga _1-b N (0 ≦ b <1) doped with Mg as a p-type impurity, but is preferably Al _b Ga _{1. -b N (0 ≦ b <1} ) and it is desirable that the super lattice structure of the Mg-doped _{in c Ga 1-c N (} 0 ≦ c <1). When the p-type cladding layer has a superlattice structure, the resistivity decreases, so that an element having a high light emission output can be obtained while V _f and the threshold value can be decreased. When this layer has a superlattice structure, the thickness of the nitride semiconductor layer constituting the superlattice is adjusted to 100 angstroms or less, more preferably 70 angstroms or less, and most preferably 50 angstroms or less.
[0021]
Next, in the present invention, the p-type contact layer 9 is made of GaN doped with Mg as a p-type impurity, and the impurity concentration is 1 × 10 ¹⁸ to 1 × 10 ²¹ / cm ³ , more preferably 5 × 10 ^{18 to} 5 × 10. ^A preferable p-type film can be obtained by adjusting to ²⁰ / cm ³ , more preferably 5 × 10 ¹⁹ to 1 × 10 ²⁰ / cm ³ .
[0022]
【Example】
Examples of the present invention will be described below, but the present invention is not limited thereto.
[Example 1]
A first embodiment will be described with reference to FIG.
The substrate 1 made of sapphire (C-plane) is set in a MOVPE reaction vessel, and the temperature of the substrate is raised to 1050 ° C. while flowing hydrogen to clean the substrate.
[0023]
(Buffer layer 2)
Subsequently, the temperature is lowered to 510 ° C., hydrogen is used as the carrier gas, ammonia and TMG (trimethyl gallium) are used as the source gas, and a buffer layer 2 made of GaN is grown on the substrate 1 to a thickness of 150 Å.
(Undoped GaN layer 3)
After growing the buffer layer 2, only TMG is stopped and the temperature is raised to 1050 ° C. Subsequently, at 1050 ° C., TMG and ammonia are similarly used as source gases, and the undoped GaN layer 3 is grown to a thickness of 1.5 μm.
[0024]
(N-type contact layer 4)
Subsequently, at 1050 ° C., the n-type contact layer 4 made of GaN doped with 4.5 × 10 ¹⁸ / cm ^{3 of} Si is used with a source gas of TMG, ammonia, and silane gas as an impurity gas, with a thickness of 2.25 μm. Grow.
[0025]
(N-side nitride semiconductor layer 5)
Next, the silane gas is stopped and an undoped AlGaN layer 5 is grown to a thickness of 0.15 μm at 1050 ° C. using TMG, TMA, and ammonia.
(Active layer 6)
Next, the temperature is lowered to 800 ° C., and an active layer 6 made of undoped In _0.35 Ga _0.65 N is grown to a thickness of 30 Å using TMG, TMI (trimethylindium), and ammonia.
[0026]
(P-side nitride semiconductor layer 7)
Next, nitrogen and TMI are stopped, the temperature is raised to 1050 ° C., and an undoped AlGaN layer 7 is grown to a thickness of 10 Å using TMG, TMA, and ammonia.
[0027]
(P-type cladding layer 8)
Subsequently, at 1050 ° C., a layer made of AlGaN doped with Mg at 1 × 10 ²⁰ / cm ^{3 is} grown at 40 Å using TMG, TMA, ammonia, Cp ₂ Mg, and then the temperature is set at 800 ° C. A stop TMI is flown and a layer made of InGaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown to a thickness of 25 Å. These operations are alternately repeated to grow a p-type cladding layer 8 made of a superlattice in which five layers are stacked.
[0028]
(P-type contact layer 9)
Subsequently, at 1050 ° C., a p-type contact layer 9 made of p-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown to a thickness of 0.15 μm using TMG, ammonia, and Cp ₂ Mg.
[0029]
After completion of the reaction, the temperature is lowered to room temperature, and the wafer is annealed in a reaction vessel at 700 ° C. in a nitrogen atmosphere to further reduce the resistance of the p-type layer.
After annealing, the wafer is taken out from the reaction vessel, a predetermined mask is formed on the surface of the uppermost p-type contact layer 9, and etching is performed from the p-type contact layer side with an RIE (reactive ion etching) apparatus. As shown, the surface of the n-type contact layer 4 is exposed.
[0030]
After etching, a light-transmitting p-electrode 10 containing Ni and Au having a thickness of 200 angstroms is formed on almost the entire surface of the p-type contact layer as the uppermost layer with a thickness of 0.5 μm, while n is exposed by etching. An n-electrode 11 containing W and Al was formed on the surface of the mold contact layer 4 to obtain an LED element.
This LED element emitted blue light with a forward voltage of 3.4 V and 468 nm at a forward voltage of 20 mA, and the light emission output was 3 mW.
[0031]
[Example 2]
An LED element was fabricated in the same manner as in Example 1 except that the active layer 6 was changed as follows.
(Active layer 6)
A barrier layer made of undoped GaN is grown at a temperature of 1050 ° C. to a thickness of 200 Å. Subsequently, the temperature is set to 800 ° C., and TMG, TMI (trimethylindium), and ammonia are used, and undoped In _0.35 Ga _0.65 N A well layer composed of 30 Å is grown to a thickness of 30 Å. Then, five barrier layers and four well layers are alternately stacked in the order of barrier + well + barrier + well +... + Barrier to grow an active layer 6 having a multiple quantum well structure with a total thickness of 1120 angstroms. Let
As a result, this LED element emitted blue light with a forward voltage of 3.6 V and 470 nm at a forward voltage of 20 mA, and the light emission output was 6.0 mW.
[0032]
[Example 3]
An LED element was fabricated in the same manner as in Example 1 except that the active layer 6 was changed as follows.
(Active layer 6)
At 800 ° C., an active layer 6 made of undoped In _0.45 Ga _0.55 N is grown to a thickness of 30 Å using TMG, TMI (trimethylindium), and ammonia.
As a result, this LED element emitted blue-green light with a forward voltage of 3.4 V and 500 nm at a forward voltage of 20 mA, and the light emission output was 2.5 mW.
[0033]
[Example 4]
In Example 1, except that the second nitride semiconductor layer 7 on the p side was removed, an LED element was produced in the same manner. As a result, an LED element having the same characteristics as that of Example 1 was obtained. .
[0034]
[Example 5]
An LED element was fabricated in the same manner as in Example 1 except that the p-type cladding layer 8 was changed as follows.
(P-type cladding layer 8)
A p-type cladding layer 8 made of AlGaN doped with Mg at 1 × 10 ²⁰ / cm ³ was grown at a thickness of 250 Å at 1050 ° C. using TMG, TMA, ammonia, and Cp ₂ Mg.
Other than that, an LED element was produced in the same manner as in Example 1. As a result, an LED element having the same characteristics was obtained although it was slightly inferior to Example 1.
[0035]
【The invention's effect】
As described above, according to the present invention, in a nitride semiconductor device having a low resistance structure in which an n-type contact layer is a nitride semiconductor doped with a high concentration of impurities, the n-type contact layer is provided between the n-type contact layer and the active layer. An undoped first nitride semiconductor layer is provided with a thickness of 2000 angstroms or less, and an undoped second nitride semiconductor layer is provided with a thickness of 100 angstroms or less between the p-type cladding layer and the active layer. . With such a structure, Vf and the threshold value are reduced, and an element with high light emission output can be obtained. For example, an LED element that maintains 2.5 mW at 20 mA can be obtained even if the n-type contact layer is highly doped with Si as 1 × 10 ²¹ / cm ³ as an n-type impurity.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of an LED element according to an embodiment of the present invention.
[Brief description of symbols]
1 ... substrate
2 ... buffer layer,
3 ... GaN layer,
4 ... n-type contact layer,
5 ... n-side nitride semiconductor layer,
6 ... active layer,
7... P-side nitride semiconductor layer,
8 ... p-type cladding layer,
9: p-type contact layer,
10 ... p electrode,
11: n electrode.

Claims (5)

an n-type contact layer made of GaN doped with an n-type impurity, an active layer containing In and Ga and having a quantum well, a p-type cladding layer containing p-type AlGaN doped with a p-type impurity, and a p-type In a nitride semiconductor device having a p-type contact layer made of GaN doped with impurities in order,
An undoped first nitride semiconductor layer having a thickness of 10 angstroms to 0.2 μm is formed between the n-type contact layer and the active layer in contact with the active layer,
Further, an undoped second nitride semiconductor layer made of AlGaN having a thickness of 10 angstroms to 100 angstroms is formed between the p-type cladding layer and the active layer in contact with the p-type cladding layer and the active layer. Has been
The p-type cladding layer is a layer made of a superlattice of Mg-doped Al _b Ga _1-b N (0 <b <1) and Mg-doped In _c Ga _1-c N (0 ≦ c <1). A nitride semiconductor light emitting device characterized by that. 2. The nitride semiconductor light emitting device according to claim 1, wherein the n-type contact layer is doped with Si as 1 × 10 ¹⁸ / cm ³ or more and 1 × 10 ²¹ / cm ³ or less as an n-type impurity. element. The nitride semiconductor light-emitting element according to claim 1, wherein the first nitride semiconductor layer is an undoped AlGaN layer. The nitride semiconductor light emitting device according to any one of claims 1 to 3 , wherein the active layer has a single quantum well structure. The thickness of the second semiconductor layer made of the p-side of the undoped nitride semiconductor light emitting device according to any one of claims 1 to 4, characterized in that the 10 Å

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