JP2000091705A - Gallium nitride based semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a gallium nitride based semiconductor light emitting element represented by a specified formula having low operating current and voltage by decreasing the band gap of a first p-type layer toward a second p-type layer and setting it equal to or larger than the band gap at the interface of first and a second p-type layers. SOLUTION: The gallium nitride based semiconductor light emitting element has a layer structure sandwiching a p-type layer and an n-type layer represented by a general formula InxAlyGa1-x-yN (0<=x<=1, 0<=y<=1, 0<=x+y<=1). A p-type AlGaN layer 8 has six layer structure of p-type Al0.19Ga0.81N, and the like, (14-19) sequentially from the side of interface to an active layer 7 and has total thickness of 200 Å. The p-type Al0.19Ga0.81N layer 14 has large Al composition so that it has a large conduction band barrier. The p-type AlGaN layer 14-19 has Al composition decreasing toward a o-type GaN optical guide layer 9 and the valence band discontinuity at each interface is suppressed to be small.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a high luminous efficiency,
The present invention also relates to a gallium nitride based semiconductor light emitting device having a low operating voltage.

[0002]

2. Description of the Related Art The general formula In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦
The gallium nitride based semiconductor represented by 1, 0 ≦ x + y ≦ 1) has a large band gap, and is expected to be applied to light emitting diodes and semiconductor lasers from green to ultraviolet.

FIG. 10 is a sectional view showing the structure of a conventional gallium nitride-based light emitting diode (eg, S. Nakamu).
ra et al., Japanese Journal of Applied Physics 34, L1
Pages 332 to L1335 (1995)). In FIG. 10, the layer structure of the gallium nitride based light emitting diode is as follows:
GaN buffer layer 1 on (0001) plane sapphire substrate 101
02, 4 μm thick n-type GaN contact layer 103, thickness 30
In In _0.45 Ga _0.55 N active layer 104, 1000 ｐ thick p-type Al
_{It comprises a 0.2} Ga _0.8 N layer 105 and a p-type GaN contact layer 106 having a thickness of 0.5 μm. n in contact with n-type contact layer 103
The p-electrode 1 is in contact with the electrode 107 and the p-type contact layer 106.
08 is formed. High-intensity blue light emission is obtained with a light-emitting diode using such a layer structure.

FIG. 11 is a schematic view of a band structure around the active layer 104 of the light emitting diode shown in FIG. FIG.
Is a band diagram in a flat band without considering doping for simplicity. p-type Al _0.2 Ga _0.8 N layer 105
Has a large band gap difference from the active layer 104 and a large hetero-barrier on the conduction band side. As a result, it has a function of blocking electrons from overflowing from the active layer 104 to the p-type layer side. Since the p-type AlGaN has a property that the resistance increases as the Al composition increases, such an electron blocking function is provided by a p-type Al having a small thickness and a large Al composition.
This is performed in the GaN layer 105, and the other p-type layers are made of p-type GaN having a relatively low resistance, thereby suppressing the electron overflow and the increase in the element resistance.

FIG. 12 is a sectional view of a layer structure of a conventional gallium nitride based semiconductor laser (for example, S. Nakamu
ra et al., Applied Physics Letters 70, 868-870 (1997)). In FIG. 12, the layer structure of this gallium nitride based laser has a (0001) plane sapphire substrate 111.
GaN buffer layer 112, n-type GaN contact layer 113 with a thickness of 3 μm, n-type In _0.05 Ga _0.95 N crack prevention layer 114 with a thickness of 0.1 μm, n-type Al _0.07 Ga _0.93 N cladding layer 1 with a thickness of 0.5 μm
15. n-type GaN optical guide layer 116 having a thickness of 0.1 μm and a thickness of 50 °
In _0.14 Ga _0.86 N quantum well layer and 100 mm thick In _0.02 Ga _0.98
Three-period multiple quantum well structure active layer 11 composed of N barrier layer
7, 200-mm thick p-type Al0.2Ga0.8N layer 118, 0.1 μm thick
P-type GaN optical guide layer 119, p-type Al _0.07 Ga having a thickness of 0.5 μm
_{It comprises a 0.93} N cladding layer 120 and a 0.2 μm thick p-type GaN contact layer 121. An n-electrode 122 is formed in contact with the n-type contact layer 113, and a p-electrode 123 is formed in contact with the p-type contact layer 121. Room temperature continuous oscillation is realized by a semiconductor laser using such a layer structure.

FIG. 13 is a schematic diagram showing a band structure around the active layer 117 of the semiconductor laser shown in FIG. FIG. 13 is a band diagram of a flat band in which doping is not considered for simplicity. The semiconductor laser shown in FIG. 12 has the same function as the light emitting diode shown in FIG. 10 in that the electron overflow blocking function is performed by the p-type AlGaN layer 118 having a small thickness and a large Al composition. The layer is made of p-type AlGaN and p-type GaN having a relatively low resistance and a low Al composition, thereby suppressing electron overflow and suppressing an increase in element resistance. In the case of a semiconductor laser, unlike a light emitting diode, a p-type GaN light guide layer 119 and a p-type Al _0.07 layer having a low refractive index are used to increase light confinement in the active layer 117.
The Ga _0.93 N cladding layer 120 is required, but the Al composition of the p-type cladding layer 120 is suppressed to a size that does not increase the resistivity so much.

[0007]

As described above, in the light emitting diode and the semiconductor laser shown in FIGS. 10 and 12, a thin p-type AlGaN having a large Al composition is provided in contact with the active layer, and other p-type layers are formed. With AlGaN or G with low Al composition
By adopting aN, the two requirements of suppressing the electron overflow and reducing the resistance are achieved. However, as shown in FIG. 11 and FIG.
The p-type GaN layer in contact with the N layer has a large valence band heterobarrier when holes flow to the active layer. GaN and AlG
Since the effective mass of holes is very large in aN, holes need to be piled up in the p-type GaN layer in contact with the thin-film p-type AlGaN layer in order to flow holes into the active layer. As a result, an extremely large electric field is generated in the thin p-type AlGaN layer.

FIG. 14 shows a band diagram around the active layer when the hole current is large in the semiconductor laser of FIG. As a result of such a large electric field generated in the thin p-type AlGaN layer, the electron drift current and the electron tunnel current from the active layer toward the p-type layer increase, and the overflow of electrons increases. Therefore, electrons are not effectively confined in the active layer, and the oscillation threshold current increases. Further, an electric field generated due to hole pile-up causes an extra device voltage. Such a situation is the same for the light emitting diode shown in FIG.

In order to further increase the luminous efficiency and lower the voltage of a gallium nitride based light emitting diode, or to further lower the threshold and lower the voltage of a semiconductor laser, electron drift / tunnel current caused by such hole pile-up. ,
And extra voltage reduction is required. In particular, since a semiconductor laser requires a higher operating current density than a light emitting diode, reduction of these is important.

The present invention has been made in view of the above problems, and has as its object to provide a gallium nitride based semiconductor light emitting device having a low operating current and a low operating voltage.

[0011]

According to the present invention, there is provided a compound represented by the general formula: In _x Al _y
Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ x + y ≦ 1) A layer in which an active layer is sandwiched between a p-type layer and an n-type layer composed of a gallium nitride-based semiconductor represented by In the gallium nitride based semiconductor light emitting device having a structure, the p-type layer has a multilayer structure including at least a first p-type layer and a second p-type layer in contact with the first p-type layer in order from the active layer side, and The band gap of the first p-type layer in the region including the vicinity of the interface with the second p-type layer, the second p-type layer
And the band gap at the interface between the first p-type layer and the second p-type layer is smaller than that of the second p-type layer. The first
A gallium nitride-based semiconductor light-emitting device characterized by having a band gap equal to or larger than the band gap at the interface with the p-type layer.

In this case, in the first p-type layer, a region where the band gap is stepwise or continuously reduced toward the second p-type layer is at least the second p-type layer.
Any region including the vicinity of the interface with the mold layer may be used.Even if the band gap is reduced toward the second p-type layer over the entire first p-type layer, the band gap may be in the middle of the first p-type layer. It may be either smaller from the first to the second p-type layer side.

Further, the present invention provides that the band gap of the first p-type layer is stepwise or continuously from the active layer side to the second p-type layer in a region near the interface with the active layer. 2. The gallium nitride based semiconductor light emitting device according to claim 1, wherein the size is larger.

In this case, in the first p-type layer, the region where the band gap increases from the active layer side toward the second p-type layer is limited to the region near the interface with the active layer. ,
In the region near the second p-type layer in the first p-type layer, as described above, the band gap must be reduced stepwise or continuously toward the second p-type layer.
In the present invention, the first p-type layer can be formed in contact with the active layer.

Further, in the present invention, the active layer is formed of a single or multiple quantum well having InGaN or GaN as a quantum well, and the first and second p-type layers are formed of a general formula Al _z Ga _{1− z}
It is preferable to be represented by N (0 ≦ z ≦ 1).

Further, in the present invention, the second p-type layer is in contact with a third p-type layer on the opposite side of the first p-type layer, and the second p-type layer has a refractive index of It can be configured to be higher than the average refractive index of the first p-type layer and the refractive index of the third p-type layer. In this case, in the semiconductor laser, the second p-type layer functions as a light confinement layer.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described in detail based on embodiments with reference to the drawings. Hereinafter, embodiments of the present invention will be described by taking a semiconductor laser as an example among gallium nitride based semiconductor light emitting devices. The effect of the invention is the same for a light emitting diode.

Embodiment 1 FIG. 1 is a view showing a nitriding process according to the present invention.
Sectional view of the layer structure of the first embodiment of the gallium-based semiconductor laser
It is. FIG. 1 shows a gallium nitride based laser of the present invention.
Is formed on a sapphire substrate 1 having a (0001) plane as a surface.
GaN buffer layer 2, n-type GaN contact layer with thickness of 3μm
3. n-type In with thickness of 0.1μm_0.05Ga_0.95N crack prevention layer
4. 0.5μm thick n-type Al_0.07Ga_0.93N clad layer 5, thickness
0.1 μm n-type GaN optical guide layer 6, 50 mm thick In_0.14Ga_0.86
N quantum well layer and 100 mm thick In_0.02Ga_0.98From the N barrier layer
Three-period multiple quantum well structure active layer 7, p-type AlGaN layer
8, p-type GaN optical guide layer 9 with a thickness of 0.1 μm, p-type GaN with a thickness of 0.5 μm
Type Al_0.07Ga_0.93N cladding layer 10, 0.2 μm thick p-type GaN
And a contact layer 11. On the n-type contact layer 3
The p-electrode 13 is formed on the n-electrode 12 and the p-type contact layer 11.
Is done. FIG. 2 shows the vicinity of the active layer 7 and the p-type AlGaN layer 8.
1 shows a schematic view of a band structure. Figure 2 shows the dough for simplicity.
Band diagram in case of flat band without considering ping
It has become. The p-type AlGaN layer 8 is on the interface side with the active layer 7.
In order from the 50mm thick p-type Al_0.19Ga_0.81N layer 14, thickness 3
0Å p-type Al_{0.1 6}Ga_0.84N layer 15, 30 mm thick p-type Al_0.13
Ga_0.87N layer 16, 30 mm thick p-type Al_0.1Ga _0.9N layer 17, thickness
30 mm p-type Al_0.07Ga_0.93N-layer 18, p-type Al 30 mm thick
_0.04Ga_{0.9 6}It has a six-layer structure with the N layer 19,
The thickness is 200 mm. p-type Al _0.19Ga_0.81N layer 14
Has a sufficiently large conduction band barrier for electrons in the active layer
Has a large Al composition. p-type AlGaN layer 14
19 stepwise toward the p-type GaN light guide layer 9
Al composition decreases, and valence band discontinuity at the interface of each layer always occurs
It is kept small.

FIG. 6 is a band diagram near the active layer when a high current is injected in the gallium nitride based laser according to the first embodiment of the present invention. The p-type AlGaN layers 14 to 19 in the p-type AlGaN layer 8 are:
Since the Al composition decreases stepwise toward the p-type GaN light guide layer 9, the valence band discontinuity at the interface between the layers is always kept small, and the pile-up of the hole hardly occurs. Therefore, the p-type Al _0.19 Ga
_{In the 0.81} N layer 14, the electric field is suppressed, and the drift of the active layer electrons and the overflow due to the tunnel are reduced as compared with the semiconductor laser according to the related art. Further, since an extra voltage due to hole pile-up is not applied to the p-type AlGaN layer 8, the operating voltage can be reduced. As described above, the operation current and the operation voltage of the semiconductor laser can be reduced by implementing the present invention.

[Embodiment 2] FIG. 3 is a schematic diagram showing a band structure near an active layer 7 and a p-type AlGaN layer 8 in a second embodiment of the gallium nitride based laser according to the present invention.
FIG. 3 is a band diagram in the case of a flat band in which doping is not considered for simplicity. Example 2
Is compared with the laser of Example 1 shown in FIG.
Only the internal structure of the aN layer 8 is different. In the second embodiment, the p-type AlGaN layer 8 is formed in order from the interface side with the active layer 7.
P-type Al _0.19 thickness 50 Å Ga _0.81 N layer 20, Al _0.19 Ga _0.81 layer thickness 150 Al composition from N to Al _{0. 04} Ga _0.96 N is decreased linearly
Å has a two-layer structure with the p-type AlGaN layer 21. p
The type Al _0.19 Ga _0.81 N layer 20 has a large Al composition so as to have a sufficiently large conduction band barrier for electrons in the active layer. In the p-type AlGaN layer 21, since the Al composition continuously decreases toward the p-type GaN light guide layer 9, the valence band discontinuity is always small.

FIG. 7 is a band diagram near the active layer when a high current is injected in the gallium nitride based laser according to the second embodiment of the present invention. Since the p-type AlGaN layer in the p-type AlGaN layer 8 has a continuously decreasing Al composition toward the p-type GaN optical guide layer 9,
The valence band discontinuity at each position is always kept small, and the pile-up of holes is hard to occur. Therefore, the electric field is suppressed particularly in the p-type AlGaN layer 20, and the drift of the active layer electrons and the overflow due to the tunnel are reduced as compared with the semiconductor laser according to the related art. Also, p-type Al
Since an extra voltage due to hole pile-up is not applied to the GaN layer 8, the operating voltage can be reduced. As mentioned above,
By implementing the present invention, the operating current and operating voltage of the semiconductor laser can be reduced.

[Embodiment 3] FIG. 4 shows the nitriding process according to the present invention.
In the third embodiment of the gallium-based laser, the active layer 7 and the
And a schematic diagram of a band structure near the p-type AlGaN layer 8.
FIG. 4 shows a flat without considering doping for simplicity.
The band diagram is for a band. Example 3
Is compared with the laser of Example 1 shown in FIG.
Only the internal structure of the aN layer 8 is different. Example 3
In addition, the p-type AlGaN layer 8 is sequentially formed from the interface side with the active layer 7.
10mm thick p-type Al_0.19Ga_0.81N-layer 22, 10 mm thick p-type A
l_0.2Ga _0.8N layer 23, 10 mm thick p-type Al_0.21Ga_0.79N layer 2
4. 10mm thick p-type Al_0.22Ga_{0.7 8}N layer 25, thickness 10mm
p-type Al_0.23Ga_0.77N layer 26, p-type Al 30 mm thick_0.19Ga
_0.81N-layer 27, p-type Al 30 mm thick_0.15Ga_0.85N layer 28, thickness
30 mm p-type Al_0.11Ga_0.89N-layer 29, p-type Al 30 mm thick
_0.07Ga_0.93N-layer 30, p-type Al 30 mm thick_0.03Ga_0.97N layer 3
1 and 10 layers. p-type Al_0.19Ga_0.81
The N layer 22 has a conduction band barrier large enough for the electrons of the active layer.
It has a large Al composition to have a rear. p-type AlGa
In the N layers 22 to 26, toward the p-type GaN light guide layer 9,
The Al composition increases stepwise. Also, p-type AlGaN
In layers 27 to 31, the layers move toward the p-type GaN light guide layer 9.
Since the Al composition is reduced in steps, the valence at each interface is
Child band discontinuity is always kept small.

FIG. 8 is a band diagram near the active layer when a high current is injected in the gallium nitride based laser according to the third embodiment of the present invention. The p-type AlGaN layers 22 to 26 in the p-type AlGaN layer 8 are:
The Al composition increases stepwise toward the p-type GaN light guide layer 9, and the Al composition decreases stepwise toward the p-type GaN light guide layer 9 in the p-type AlGaN layers 27 to 31.
In the p-type AlGaN layers 27 to 31, as in the first embodiment, the valence band discontinuity at the interface between the respective layers is always kept small, and the structure is such that the pile-up of holes hardly occurs. Further, the p-type AlGaN layers 22 to 26
Since the l composition is increased, even if an electric field is generated by the hole current, it can be canceled. Therefore, the electric field can be further suppressed as compared with the first and second embodiments, the drift of the active layer electrons and the overflow due to the tunnel can be reduced, and the operating voltage can be reduced. As mentioned above,
By implementing the present invention, the operating current and operating voltage of the semiconductor laser can be reduced.

[Embodiment 4] FIG. 5 is a schematic diagram showing a band structure near an active layer 7 and a p-type AlGaN layer 8 in a gallium nitride based laser according to a fourth embodiment of the present invention.
FIG. 5 is a band diagram in the case of a flat band in which doping is not considered for simplicity. Example 4
Is compared with the laser of Example 1 shown in FIG.
Only the internal structure of the aN layer 8 is different. In the fourth embodiment, the p-type AlGaN layer 8 is
_A 50-mm thick p-type AlGaN layer 32 in which the Al composition continuously increases from _0.19 Ga _0.81 N to Al _0.23 Ga _0.77 N, Al _0.23 Ga _0.77 N
And a p-type AlGaN layer 33 with a thickness of 150 ° in which the Al composition is continuously reduced from Al to Al _0.03 Ga _0.97 N. At the interface with the active layer 7, the p-type AlGaN layer 32
It has a large Al composition so as to have a sufficiently large conduction band barrier for electrons in the active layer. In the p-type AlGaN layer 33, since the Al composition decreases continuously toward the p-type GaN light guide layer 9, the valence band discontinuity is always kept small.

FIG. 9 is a band diagram near the active layer when a high current is injected in the gallium nitride based laser according to the fourth embodiment of the present invention. In the p-type AlGaN layer 32 in the p-type AlGaN layer 8, the Al composition continuously increases toward the p-type GaN optical guide layer 9, and the p-type AlGaN layer 32
In the AlGaN layer 33, the Al composition continuously decreases toward the p-type GaN light guide layer 9. In the p-type AlGaN layer 33, the valence band discontinuity at each position is always kept small as in the second embodiment, and the structure is such that the pile-up of holes hardly occurs. Further, in the p-type AlGaN layer 32, A
Since the l composition is increased, even if an electric field is generated by the hole current, it can be canceled. Therefore, the electric field can be further suppressed as compared with the first and second embodiments, the drift of the active layer electrons and the overflow due to the tunnel can be reduced, and the operating voltage can be reduced. As mentioned above,
By implementing the present invention, the operating current and operating voltage of the semiconductor laser can be reduced.

In the above description of the first to fourth embodiments, the embodiment of the present invention has been described by taking a semiconductor laser as an example, but the present invention is also effective for a light emitting diode.

In the first and third embodiments, the example in which the Al composition is changed stepwise in the p-type AlGaN layer 8 has been described. However, the number of steps and the amount of change in the composition between adjacent steps are different from those of the adjacent steps. If the difference in band gap between them is sufficiently small, an Al composition profile other than that shown in the examples may be used. For example, the difference in band gap between adjacent steps may be set to about 0.3 eV or less, preferably 0.03 eV or less.

In Examples 2 and 4, p-type AlGaN
Although the example in which the Al composition is changed linearly and continuously in the layer 8 has been described, other Al composition profiles may be used at each position.
If the Al composition change is sufficiently small, there is no problem in practicing the invention.

Further, in the present invention, if the change of the band gap in the layer thickness direction is similar to that of the embodiment, p
Even if a p-type InAlGaN layer is used instead of the p-type AlGaN layer 8, the p-type G
Instead of the aN light guide layer 9, a p-type InAlGaN layer may be used.

[0030]

According to the present invention, a gallium nitride based semiconductor laser having a low operating current and a low operating voltage can be realized.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a gallium nitride based laser of Examples 1 to 4 of the present invention.

FIG. 2 is a band diagram in a flat band near an active layer in the gallium nitride based laser of Example 1.

FIG. 3 is a band diagram in a flat band near an active layer in the gallium nitride based laser of Example 2.

FIG. 4 is a band diagram in a flat band near an active layer in the gallium nitride based laser of Example 3.

FIG. 5 is a band diagram in a flat band near an active layer in the gallium nitride based laser of Example 4.

FIG. 6 is a band diagram near an active layer when a high current is injected in the gallium nitride based laser of Example 1.

FIG. 7 is a band diagram near the active layer when a high current is injected in the gallium nitride based laser of Example 2.

FIG. 8 is a band diagram near the active layer when a high current is injected in the gallium nitride based laser of Example 3.

FIG. 9 is a band diagram near the active layer when a high current is injected in the gallium nitride based laser of Example 4.

FIG. 10 is a cross-sectional view of a conventional gallium nitride based semiconductor light emitting diode.

FIG. 11 is a band diagram in a flat band near an active layer in a conventional gallium nitride based semiconductor light emitting diode.

FIG. 12 is a cross-sectional view of a conventional gallium nitride based semiconductor laser.

FIG. 13 is a band diagram in a flat band near an active layer in a conventional gallium nitride based semiconductor laser.

FIG. 14 is a band diagram near an active layer when a high current is injected in a conventional gallium nitride based semiconductor laser.

[Explanation of symbols]

Sapphire substrate with 1,101,111 (0001) plane as the surface 2, 102, 112 GaN buffer layer 3, 103, 113 n-type GaN contact layer 4, 114 n-type In _0.05 Ga _0.95 N crack prevention layer 5, 115 n-type Al _0.07 Ga _0.93 N cladding layer 6, 116 n-type GaN optical guiding layer 7, 117 active layer with multiple quantum well structure 8, 118 p-type AlGaN layer 9, 119 p-type GaN optical guiding layer 10, 120 p-type Al _0.07 Ga _0.93 N cladding layer 11, 106, 121 p-type GaN contact layer 12, 107, 122 n-electrode 13, 108, 123 p-electrode 14, 20 p-type Al _0.19 Ga _0.81 N layer 15 p-type Al _0.16 Ga _0.84 N layer 16 p-type Al _0.13 Ga _0.87 N layer 17 p-type Al _0.1 Ga _0.9 N layer 18 p-type Al _0.07 Ga _0.93 N layer 19 p-type Al _0.04 Ga _0.96 N layer 21 p-type AlGaN layer with continuously changing Al composition 22 p-type Al _0.19 Ga _0.81 N layer 23 p-type Al _0.2 Ga _0.8 N layer 24 p-type Al _0.21 Ga _0.79 N layer 25 p-type Al _0.22 Ga _0.78 N layer 26 p-type Al _0.23 Ga _0.77 N layer 27 p-type Al _0.19 Ga _0.81 N layer 28 p-type Al _0.15 Ga _0.85 N layer 29 p-type Al _0.11 Ga _0.89 N layer 30 p-type Al _0.07 Ga _0.93 N layer 31 p _-Type Al _0.03 Ga _0.97 N layer 32, 33 p-type AlGaN layer with continuously changing Al composition 104 In _0.45 Ga _0.55 N active layer 105 p-type Al _0.2 Ga _0.8 N layer

Claims (5)

[Claims] The general formula In _x Al _y Ga _1-xy N (0 ≦ x ≦ 1, 0 ≦ y ≦
1, 0 ≦ x + y ≦ 1) a gallium nitride-based semiconductor light emitting device having a layer structure in which an active layer is sandwiched between a p-type layer and an n-type layer composed of a gallium nitride-based semiconductor represented by the following formula: A multilayer structure including at least a first p-type layer and a second p-type layer in contact with the first p-type layer from the active layer side, and the band gap of the first p-type layer is the second p-type layer.
In a region including the vicinity of the interface with the mold layer, it is stepwise or continuously reduced toward the second p-type layer side,
And whether the band gap at the interface of the first p-type layer with the second p-type layer is equal to the band gap at the interface of the second p-type layer with the first p-type layer. Or a gallium nitride based semiconductor light emitting device characterized by being larger. 2. The band gap of the first p-type layer is:
In the region near the interface with the active layer, the second
2. The gallium nitride-based semiconductor light emitting device according to claim 1, wherein the size increases stepwise or continuously toward the p-type layer. 3. The gallium nitride based semiconductor light emitting device according to claim 1, wherein said first p-type layer is formed in contact with said active layer. 4. The active layer is composed of a single or multiple quantum well having InGaN or GaN as a quantum well, and the first and second p-type layers are formed of a general formula Al _z Ga _{1 -z} N (0 The gallium nitride-based semiconductor light emitting device according to any one of claims 1 to 3, wherein the gallium nitride-based semiconductor light-emitting device is formed of a gallium nitride-based semiconductor represented by ≤z≤1). 5. The second p-type layer is in contact with a third p-type layer on the opposite side of the first p-type layer, and the second p-type layer has a refractive index of the second p-type layer. 5. The gallium nitride-based semiconductor light emitting device according to claim 1, wherein the average refractive index of the first p-type layer and the refractive index of the third p-type layer are larger.