JP3427265B2 - Nitride semiconductor device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting element such as a light emitting diode (LED), a laser diode (LD), a solar cell, an optical sensor, a light receiving element, or a nitride used for an electronic device such as a transistor or a power device. Semiconductor (for example, In _a Al _b Ga _{1 -ab} N, 0 ≦ a,
0 ≦ b, a + b ≦ 1) element.

[0002]

2. Description of the Related Art Nitride semiconductors have been put to practical use as materials for high-intensity blue LEDs and pure green LEDs in various light sources such as full-color LED displays, traffic lights, and image scanner light sources. These LED elements are basically
A GaN buffer layer on the sapphire substrate and Si
N-side contact layer made of doped GaN and InGa having a single quantum well structure (SQW: Single-Quantum-Well)
Multiple quantum well structure (M
QW: Multi-Quantum-Well) active layer and Mg-doped A
p-side clad layer made of lGaN and Mg-doped GaN
And a p-side contact layer composed of the above are sequentially stacked. At 20 mA, a blue LED having an emission wavelength of 450 nm has a power of 5 mW and an external quantum efficiency of 9.1% and 520 nm.
The green LED shows excellent characteristics such as 3 mW and external quantum efficiency of 6.3%. The active layer having a quantum well structure is expected to improve the light emission output due to the characteristics of the structure.

[0003]

However, when the above-mentioned conventional element is used as an LED element for a light source for illumination, an outdoor display exposed to direct sunlight, etc., the light emission output is not sufficiently satisfactory. As described above, the quantum well structure active layer is expected to dramatically improve the light emission output.
It is difficult to make full use of the expected potential. Further, lowering the forward voltage (Vf) of the element and improving the electrostatic breakdown voltage lead to widening the versatility of the element and improving the reliability of the element. Therefore, the object of the present invention is to improve the reliability of the element and to expand the range of application to various application products, so that the light emission output can be further improved and the electrostatic breakdown voltage with a low Vf is good. Another object of the present invention is to provide another nitride semiconductor device.

[0004]

That is, the present invention can achieve the object of the present invention by the constitutions (1) to (7) below. (1) Between the n-type nitride semiconductor and the p-type nitride semiconductor,
In the nitride semiconductor device having an active layer, the n-type nitride semiconductor is an n-type contact layer made of Al _g Ga _1-g N (0 ≦ g ≦ 0.2), a GaN layer and In _p Ga _{1-. p} N
An n-type multilayer film layer formed by stacking (0 <p <1) layers,
An n-side first multilayer film layer having a lower layer of undoped GaN and an intermediate layer of GaN doped with n-type impurities between the n-type contact layer and the n-type multilayer film layer; Nitride semiconductor device. (2) The nitride semiconductor device according to (1), wherein the n-side first multilayer film layer further includes an upper layer made of an undoped nitride semiconductor. (3) The undoped GaN lower layer has a thickness of 10
The nitride semiconductor device according to (1) or (2) above, which is 0 to 10000Å. (4) The n-type multilayer film layer is formed by laminating an undoped GaN layer and an undoped In _p Ga _1-p N (0 <p <1) layer, and is any one of (1) to (3) above. 1. The nitride semiconductor device according to one. (5) The p-type nitride semiconductor is Al _x Ga _{1 -x} N (0 <
(1) which includes a p-type multilayer film layer having a superlattice structure in which x <1) and In _y Ga _1-y N (0 ≦ y <1) are stacked.
The nitride semiconductor device according to any one of (4). (6) The nitride semiconductor device according to (5), wherein the number of nitride semiconductor layers forming the p-type multilayer film layer is smaller than the number of nitride semiconductor layers forming the n-type multilayer film layer. (7) The nitride semiconductor device according to (6), wherein the p-type multilayer film layer is modulation-doped.

That is, according to the present invention, as described above, the n-type multilayer film layer and the p-type multilayer film layer having different compositions and / or the number of layers are formed so as to sandwich the active layer. By specifying the layer structure near the active layer of the device structure, it is possible to improve the light emission output, reduce Vf, and provide a nitride semiconductor device having a good electrostatic breakdown voltage.

The active layer having a quantum well structure has a possibility of improving the light emission output, but it has been difficult for the conventional element to fully exhibit the possibility of the quantum well structure.

On the other hand, the inventors of the present invention have conducted various studies in order to fully exhibit the performance of the active layer of the quantum well structure. As a result, the inventors have found that the composition and / or the number of layers are close to or in contact with the active layer. By forming different n-type multilayer film layers and p-type multilayer film layers, the performance of the active layer is satisfactorily drawn to improve the light emission output, and at the same time, reduce Vf and improve the electrostatic breakdown voltage. I was able to. The reason for this is not clear, but in addition to improving the crystallinity of the active layer and the crystallinity of the layer forming the p-electrode, a multilayer structure probably improves the crystallinity, and further, the composition and / or The difference in crystal properties between the n-type multilayer film layer and the p-type multilayer film layer due to the difference in the number of layers synergistically affects the entire device and has a positive effect on the device performance (emission output, Vf, electrostatic breakdown voltage). Etc.) is considered to be improved.

In the present invention, the multi-layer film layer is formed by laminating at least two single nitride semiconductor layers of at least two kinds having different compositions, and adjacent single nitride semiconductor layers. A plurality of single nitride semiconductor layers are laminated so that the compositions are different from each other. Further, in the present invention, the difference in composition of the nitride semiconductor forming the n-type multilayer film layer and the composition of the nitride semiconductor forming the p-type multilayer film layer means that each of the multilayer film layers is single. Although the composition of the nitride semiconductor may be the same, it means that the overall layer structure (overall composition) of the multilayer film layer formed by laminating a plurality of single nitride semiconductor layers does not match. That is, the composition of the n-type multilayer film layer and the composition of the p-type multilayer film layer may partially match, but the composition of the nitride semiconductor layer is adjusted so as not to completely match. In the present invention, the difference in the number of laminated layers means that at least one or more p-type or n-type nitride semiconductors forming a multilayer film layer are laminated.

Further, in the present invention, when the number of nitride semiconductor layers forming the p-type multilayer film layer is smaller than the number of nitride semiconductor layers forming the n-type multilayer film layer, the light emission output, Vf. Also, it is preferable because the characteristics of electrostatic withstand voltage can be improved. In the present invention, the number of p-type multilayer film layers stacked may be at least one layer smaller than the number of n-type multilayer film layers stacked.

Further, in the present invention, the n-type multilayer film layer is Al _z G
a _1-z N (0 ≦ z <1) and In _p Ga _{1 -p} N (0 <p <
1) and the p-type multilayer film layer is Al _x Ga _{1 -x} N
By including (0 <x <1) and In _y Ga _1-y N (0 ≦ y <1), better emission output, Vf, and electrostatic breakdown voltage can be obtained. Still further, the present invention provides p
When the type multilayer film layer and / or the n-type multilayer film layer is modulation-doped, the light emission output, Vf, and electrostatic withstand voltage can be improved. Further, in the present invention, the modulation dope is
In a single nitride semiconductor layer forming a multilayer film layer, it means that adjacent nitride semiconductor layers have different impurity concentrations. One of the adjacent nitride semiconductor layers forming the multilayer film layer is undoped and the other is May be doped with impurities, and when both adjacent nitride semiconductor layers are doped with impurities, the adjacent nitride semiconductors may have different impurity concentrations.

In the present invention, when the n-type multilayer film layer 6 and the p-type multilayer film layer 8 have different compositions, the n-type multilayer film layer 6 is formed.
And the number of layers forming the p-type multilayer film layer 8 are
The number of layers may be the same or different, preferably the number of layers is different, and more preferably the number of layers of the p-type multilayer film layer is smaller than the number of layers of the n-type multilayer film layer in terms of light emission output, Vf, and electrostatic withstand voltage. preferable. In the present invention, when the n-type multilayer film layer and the p-type multilayer film layer have different numbers of layers, the composition of the n-type multilayer film layer and p
It may be the same as or different from the composition of the type multi-layer film layer, and preferably the composition is different in order to obtain the effects of the present invention as described above. Further, in the present invention, when the number of layers of the n-type multilayer film layer and the number of layers of the p-type multilayer film are different, the combination of the number of layers of n-type and p-type is not particularly limited, and p-type multilayer film layers 8 and n Any combination may be used as long as the type multilayer film layer 6 has a different number of layers, and preferably, as described above, p
In order to obtain the effects of the present invention, it is preferable that the number of the n-type multilayer film layers is smaller than the number of the n-type multilayer film layers.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The n of the present invention will be described below with reference to FIG.
The nitride semiconductor having the p-type multilayer film layer and the p-type multilayer film layer will be described in more detail. FIG. 1 is a schematic cross-sectional view showing the structure of a nitride semiconductor device (LED device) which is an embodiment of the present invention. However, the present invention is not limited to this. In FIG. 1, on a sapphire substrate 1, a buffer layer 2 made of GaN, an undoped GaN layer 3, an n-type contact layer 4 made of Si-doped GaN, and undoped Ga.
It has a structure in which an N layer 5, an n-type multilayer film layer 6, an active layer 7 of InGaN / GaN having a multiple quantum well structure, a p-type multilayer film layer 8, and a p-type contact layer 9 of Mg-doped GaN are sequentially stacked. A nitride semiconductor device is shown. The composition and / or number of layers of the respective nitride semiconductors forming the n-type multilayer film layer 6 and the p-type multilayer film layer 8 are different between n-type and p-type. Here, in FIG. 1, one n-type multilayer film layer is provided as the n-type nitride semiconductor and one p-type multilayer film layer is provided as the p-type nitride semiconductor.
Two or more multilayer films may be provided on each type nitride semiconductor. For example, the undoped GaN layer 5 is formed by sequentially stacking a lower layer made of an undoped nitride semiconductor, an intermediate layer made of a nitride semiconductor doped with an n-type impurity, and a lower layer made of an undoped nitride semiconductor from the substrate side. It is preferable to improve the light emission output, Vf, and electrostatic withstand voltage when the multilayer film is formed. When the n-type nitride semiconductor has two types of n-type multilayer film layers as described above, it is sufficient that one of the two types of n-type multilayer film layers is larger than the number of p-type multilayer film layers.

First, the multilayer film layer will be described. In the present invention, the n-type multilayer film layer 6 may be composed of at least two kinds of nitride semiconductors having different compositions,
The preferred composition is AlzGa1-zN (0≤z <1)
[First nitride semiconductor layer] and InpGa1-pN (0 <p <
1) Two types of compositions including [second nitride semiconductor layer]. As a preferable composition of the first nitride semiconductor layer, the smaller the z value of the chemical formula representing the first nitride semiconductor layer, the better the crystallinity, more preferably the z value is 0.
GaN showing [zero]. The preferred composition of the second nitride semiconductor layer is InpGa1-pN having a p value of 0.5 or less in the chemical formula representing the second nitride semiconductor layer,
More preferably, it is InpGa1-pN having ap value of 0.1 or less. In the present invention, as a preferable combination of the first nitride semiconductor layer and the second nitride semiconductor layer, the first nitride semiconductor layer is GaN and the second nitride semiconductor layer is X value of 0. A combination is InXGa1-XN of 5 or less.

Further, the n-type multilayer film layer 6 having the above composition is formed by forming at least one layer of the first nitride semiconductor layer and at least one layer of the second nitride semiconductor layer, and a total of two layers or more. Three or more layers, preferably at least two or more layers each, a total of four or more layers are laminated, preferably at least seven or more layers each, and a total of 14 or more layers are laminated. The upper limit of the number of laminated layers of the first nitride semiconductor layer and the second nitride semiconductor layer is not particularly limited, but is, for example, 500 layers or less. When the number of layers exceeds 500, it takes too much time to stack the layers, and the operation tends to be complicated, or the device characteristics tend to deteriorate slightly.

The film thickness of the single nitride semiconductor layer forming the n-type multilayer film 6 is not particularly limited, but a film of at least one single nitride semiconductor layer of two or more kinds of nitride semiconductor layers. The thickness should be 100 angstroms or less, preferably 7
It is 0 angstrom or less, and more preferably 50 angstrom or less. By thinning the film thickness of the single nitride semiconductor layer forming the n-type multilayer film layer 6 in this way, the multilayer film layer has a superlattice structure and the crystallinity of the multilayer film layer is improved. The output tends to improve.

When the n-type multilayer film layer 6 is composed of the first nitride semiconductor layer and the second nitride semiconductor layer, at least one of them has a thickness of 100 angstroms or less, preferably 70 angstroms or less. It is preferably 50 angstroms or less. If at least one of the first nitride semiconductor layer and the second nitride semiconductor layer is a thin film layer having a thickness of 100 angstroms or less, each single nitride semiconductor layer has an elastic critical film thickness or less, and crystals are excellent. When a nitride semiconductor having an elastic critical film thickness or less is further grown on the nitride semiconductor layer having improved crystallinity, the crystallinity becomes better. From this, the crystallinity of the first and second nitride semiconductor layers becomes better as they are stacked, and as a result, the crystallinity of the entire n-type multilayer film layer 6 becomes better. In this way, the crystallinity of the entire n-type multilayer film layer 6 is improved, so that the light emission output of the device is improved.

The preferred film thicknesses of the first nitride semiconductor layer and the second nitride semiconductor layer are both 100 angstroms or less, preferably 70 angstroms or less, and most preferably 50 angstroms or less.
If both the first and second nitride semiconductor layers forming the n-type multilayer film layer 6 have a thickness of 100 angstroms or less, the thickness of a single nitride semiconductor layer becomes the elastic critical film thickness or less. A nitride semiconductor having good crystallinity can be grown as compared with the case of growing with a film. In addition, the first of the n-type multilayer film layer 6
When the film thicknesses of both the second nitride semiconductor layer and the second nitride semiconductor layer are 70 angstroms or less, the multilayer film layer has a superlattice structure and good crystallinity, and the active layer is grown on the superlattice structure having good crystallinity. Then, the n-type multilayer film layer 6 acts like a buffer layer, and the active layer can be grown with good crystallinity.

The total film thickness of the n-type multilayer film layer 6 is not particularly limited, but is 25 to 10000 angstroms, preferably 25 to 5000 angstroms, and more preferably 25 to 1000 angstroms. When the film thickness is in this range, the crystallinity is good and the output of the device is improved.

The position where the n-type multilayer film layer 6 is formed is not particularly limited. Even if it is formed in contact with the active layer 7, the active layer 7 is formed.
And n-type multilayer film layer 6 may be formed separately.
Are preferably formed in contact with the active layer 7. n
When the mold type multilayer film layer 6 is formed in contact with the active layer 7,
N in contact with the well layer or barrier layer which is the first layer of the active layer 7
The nitride semiconductor layer forming the multi-layer type multilayer film layer 6 includes the first
Or the second nitride semiconductor layer. As described above, the stacking order of the first nitride semiconductor layer and the second nitride semiconductor layer forming the n-type multilayer film layer 6 is not particularly limited. That is, even if stacking starts from the first nitride semiconductor and ends with the first nitride semiconductor, or stacking starts with the first nitride semiconductor and ends with the second nitride semiconductor, the second nitride semiconductor starts. The stacking may start from the first semiconductor and end with the first nitride semiconductor, or the stacking may start from the second nitride semiconductor and end with the second nitride semiconductor. Figure 1
Then, the n-type multilayer film layer 6 is formed in contact with the active layer 7, but as described above, when the n-type multilayer film layer 6 is formed apart from the active layer 7, the n-type multilayer film is formed. Layer 6 and active layer 7
A layer made of another n-type nitride semiconductor may be formed between and.

In the present invention, the single nitride semiconductor layer constituting the n-type multilayer film layer 6, for example, the first and second nitride semiconductor layers may be undoped or may be doped with n-type impurities. . In the present invention, “undoped” refers to a state in which impurities are not intentionally doped, and for example, impurities mixed by diffusion from an adjacent nitride semiconductor layer are also referred to as “undoped” in the present invention. Note that impurities mixed by diffusion often have a gradient in impurity concentration in the layer.

A single nitride half that constitutes the n-type multilayer film layer 6
The conductor layer includes a first nitride semiconductor layer and a second nitride semiconductor layer.
The first and second nitride semiconductor layers are formed of a body layer,
Both may be undoped, or both may be doped with n-type impurities.
May be added, and either one may be
It may be doped. A first nitride semiconductor layer and a first
N-type impurities are added to one of the two nitride semiconductor layers.
Or both of them are doped with n-type impurities
The difference in the concentration between the nitride semiconductor layers
The output is improved by modulation doping.
It tends to be easy. In addition, the first nitride semiconductor layer and
Both of the second nitride semiconductor layers are doped with n-type impurities.
The adjacent single nitride semiconductor layers are
Pure matter concentration may be different or the same, preferably different
It can be mentioned. To improve the crystallinity,
Is most preferred and the next adjacent one is undoped
Modulation dope, followed by modulation dope
It is the order of the loop. In addition, the first nitride semiconductor layer and the second nitride semiconductor layer
Both of the nitride semiconductor layers are doped with n-type impurities.
In this case, the impurity concentration may be high in either layer.
Yes. When the n-type impurity is doped, the impurity concentration is
5 x 10 but not limited to ^{twenty one}/cm³Below, preferably 1
× 10²⁰/cm³Below, the lower limit is 5 × 10¹⁶/cm³To key
To adjust. 5 x 10^{twenty one}/cm³More than nitride semiconductor layer
However, the crystallinity of the
It This also applies to the case of modulation doping. In the present invention
The n-type impurities include Si, Ge, Sn, S, etc.
Group IV or VI group elements are preferably selected, and more preferably S
i and Sn are used.

Next, the p-type multilayer film layer 8 will be described.
In the present invention, the p-type multilayer film layer 8 may be composed of at least two kinds of nitride semiconductors having different compositions, and a preferable composition is Al _x Ga _1-x N (0 <x
<1) [Third nitride semiconductor layer] and In _y Ga _1-y N (0
≦ y <1) and [fourth nitride semiconductor layer]. A preferred composition of the third nitride semiconductor layer is Al _x Ga _{1 -x} N having an x value of 0.5 or less in the chemical formula representing the third nitride semiconductor layer. If x exceeds 0.5, the crystallinity tends to be poor and cracking tends to occur. A preferable composition of the fourth nitride semiconductor layer is GaN having a y value of 0 [zero] in the chemical formula showing the fourth nitride semiconductor layer. When the y value is zero, a multilayer film layer having good crystallinity tends to grow easily. In the present invention, as a preferable combination of the nitride semiconductors forming the n-type multilayer film layer 8, the third nitride semiconductor layer is Al _x Ga _{1 -x} N having an x value of 0.5 or less, and
The nitride semiconductor layer may be combined with GaN.

The p-type multilayer film layer 8 having the above composition is formed by forming at least one or more third nitride semiconductor layer and at least one fourth nitride semiconductor layer, and a total of two or more layers. Three or more layers, preferably at least two or more layers each, are laminated, and a total of four or more layers are laminated. The upper limit of the stacking of the third nitride semiconductor layer and the fourth nitride semiconductor layer is not particularly limited, but in consideration of the manufacturing process such as stacking time, the device characteristics, and the like, for example, 100 layers or less can be cited.

The total film thickness of the p-type multilayer film layer 8 is not particularly limited, but is 25 to 10000 angstroms, preferably 25 to 5000 angstroms, and more preferably 25 to 1000 angstroms. When the film thickness is in this range, the crystallinity is good and the output of the device is improved. Further, in the present invention, the p-type multilayer film layer 8
When the film thickness is relatively thin within the above range, the Vf and the threshold value of the element tend to decrease.

The film thickness of a single nitride semiconductor layer forming the p-type multilayer film layer 8 is not particularly limited, but a single nitride semiconductor layer of at least one of two or more types of nitride semiconductor layers is used. The film thickness of the nitride semiconductor layer is 100 angstroms or less, preferably 70 angstroms or less, and more preferably 50 angstroms or less. Thus p
By reducing the film thickness of the single nitride semiconductor layer forming the multi-layer type multilayer film layer 8, the multilayer film layer has a superlattice structure,
Since the crystallinity of the multilayer film is improved, when a p-type impurity is added, a p-layer having a high carrier concentration and a low resistivity can be obtained, and the Vf and threshold value of the device tend to be lowered. This makes it possible to obtain good light emission output with low power consumption.

When the p-type multilayer film layer 8 is composed of the third nitride semiconductor layer and the fourth nitride semiconductor layer, at least one of the film thicknesses is 100 angstroms or less, preferably 70 angstroms or less, and most preferably. It is preferably 50 angstroms or less. When at least one of the third nitride semiconductor layer and the fourth nitride semiconductor layer is a thin film layer having a thickness of 100 angstroms or less, each single nitride semiconductor layer has an elastic critical film thickness or less and crystallinity becomes good. When a nitride semiconductor having an elastic critical film thickness or less is further grown on the nitride semiconductor layer having improved crystallinity, the crystallinity becomes better. From this, the crystallinity of the third and fourth nitride semiconductor layers becomes better as they are stacked, and as a result, the crystallinity of the entire p-type multilayer film layer 8 becomes better. Since the crystallinity of the entire p-type multilayer film layer 8 is improved in this way, a p-type layer having a high carrier concentration and a low resistivity can be obtained when p-type impurities are added, and the Vf and threshold of the device can be obtained. Values tend to decrease. This makes it possible to obtain good light emission output with low power consumption.

The preferred film thicknesses of the third nitride semiconductor layer and the fourth nitride semiconductor layer are both 100 angstroms or less, preferably 70 angstroms or less, and most preferably 50 angstroms or less. If the thicknesses of the third and fourth nitride semiconductor layers forming the p-type multilayer film layer 8 are both 100 angstroms or less, the thickness of a single nitride semiconductor layer becomes the elastic critical film thickness or less, A nitride semiconductor having good crystallinity can be grown as compared with the case of growing with a film. In addition, the third and fourth p-type multilayer film layers 8
If the thickness of both of the nitride semiconductor layers is 70 angstroms or less, the multilayer film layer has a superlattice structure, the crystallinity is good, and the Vf, threshold value, etc. of the device are easily lowered,
It is preferable for improving the light emission output.

The position where the p-type multilayer film layer 8 is formed is not particularly limited, and even if it is formed in contact with the active layer 7, the active layer 7 is formed.
And the p-type multilayer film layer 8 are preferable.
Are preferably formed in contact with the active layer 7. p
It is preferable that the mold type multilayer film layer 8 is formed in contact with the active layer 7 because the emission output is easily improved. When the p-type multilayer film layer 8 is formed in contact with the active layer 7, the nitride semiconductor layer forming the p-type multilayer film layer 8 in contact with the well layer or the barrier layer which is the first layer of the active layer 7 is The third nitride semiconductor layer or the fourth nitride semiconductor layer may be used. As described above, the stacking order of the third nitride semiconductor layer and the fourth nitride semiconductor layer forming the p-type multilayer film layer 8 is not particularly limited. That is, even if stacking starts from the third nitride semiconductor layer and ends at the third nitride semiconductor layer, or stacking starts from the third nitride semiconductor layer and ends at the fourth nitride semiconductor layer, The stacking may start from the fourth nitride semiconductor layer and end with the third nitride semiconductor layer, or the stacking may start from the fourth nitride semiconductor layer and end with the fourth nitride semiconductor layer. . In FIG. 1, the p-type multilayer film layer 8 is formed in contact with the active layer 7, but as described above, when the p-type multilayer film layer 8 is formed apart from the active layer 7, the p-type multilayer film layer 8 is formed. A layer made of another p-type nitride semiconductor may be formed between the multilayer film layer 8 and the active layer 7.

In the present invention, both the third nitride semiconductor layer and the fourth nitride semiconductor layer may be undoped, or one of them may be doped with a p-type impurity, and both may be p-type. It may be doped with impurities. p
When the third and fourth nitride semiconductor layers forming the p-type multilayer film layer 8 are both undoped, the p-type multilayer film layer 8
Is 0.1 μm or less, preferably 700 Å or less, and more preferably 500 Å or less. When the film thickness is thicker than 0.1 μm, holes are less likely to be injected into the active layer, and the light emission output tends to decrease. Moreover, if the film thickness exceeds 0.1 μm, the resistance value of the undoped layer tends to increase.
In addition, if one of the third and fourth nitride semiconductor layers is modulation-doped with a p-type impurity, the emission output tends to be improved. Further, modulation doping is preferable because a p-layer having a high carrier concentration can be easily obtained. Further, when both the third and fourth nitride semiconductor layers are doped with p-type impurities, the carrier concentration is further increased as compared with the case where one is undoped, which is preferable because Vf is lowered. When both the third and fourth nitride semiconductor layers are doped with p-type impurities, the adjacent nitride semiconductor layers may have the same impurity concentration, but preferably have different impurity concentrations (modulation dose).

In the present invention, when the p-type multilayer film layer 8 is doped with p-type impurities, the p-type impurities include Mg and Z.
Group II elements such as n, Cd, Be and Ca are preferably selected,
Preferably, Mg and Be are used. When doping with p-type impurities, the impurity concentration is adjusted to 1 × 10 ²² / cm ³ or less, preferably 5 × 10 ²⁰ / cm ³ or less. 1 x 10 ²² / cm ³
If the amount is larger than that, the crystallinity of the nitride semiconductor layer is deteriorated, and the light emission output tends to be reduced. The lower limit of the doping amount of p-type impurities is not particularly limited, but is 5 × 10 ¹⁶ / cm ³ or more.

The layers forming the element structure other than the n-type multilayer film layer 6 and the p-type multilayer film layer 8 shown in FIG. 1 will be described below, but the present invention is not limited thereto.

As the substrate 1, sapphire having a C-plane, R-plane or A-plane as a main surface, or spinel (MgA1)
_In addition to insulating substrates such as ₂ O ₄ ), SiC (6H, 4
It is possible to use a semiconductor substrate such as H, 3C), Si, ZnO, GaAs, or GaN.

As the buffer layer 2, Ga _d Al _1-d N is used.
(However, d is in the range of 0 <d ≦ 1), and the crystallinity is more significantly improved in a composition having a smaller proportion of Al. More preferably, the buffer layer 2 made of GaN is Can be mentioned. The thickness of the buffer layer 2 is 0.002-0.5 μm, preferably 0.05-
The thickness is adjusted to 0.2 μm, more preferably 0.01 to 0.02 μm. When the film thickness of the buffer layer 2 is in the above range, the crystal morphology of the nitride semiconductor becomes good, and the crystallinity of the nitride semiconductor grown on the buffer layer 2 is improved. The growth temperature of the buffer layer 2 is 200 to 900 ° C.
And preferably adjusted to a range of 400 to 800 ° C. When the growth temperature is in the above range, a good polycrystal is formed,
This polycrystal is preferable because it can improve the crystallinity of the nitride semiconductor grown on the buffer layer 2 as a seed crystal. The buffer layer 2 grown at such a low temperature may be omitted depending on the type of substrate, the growth method, and the like.

The undoped GaN layer 3 has a higher temperature than that of the previously grown buffer layer 2, for example, 900 ° C. to 11 ° C.
In _f Al _g Ga _1-fg N (0 ≦ f,
0 ≦ g, f + g ≦ 1), and the composition thereof is not particularly limited, but preferably GaN and a nitride semiconductor having few crystal defects when Al _g Ga _1-g N having a g value of 0.2 or less is used. Easy to obtain layers. There is no particular limitation on the film thickness, and the film is grown to be thicker than the buffer layer, and is usually 0.1 μm.
The film is grown to the above film thickness.

[0035] As the n-type contact layer 4 made of Si-doped GaN, similarly to the undoped GaN layer 3, an In _f
Al _g Ga _1-fg N (0 ≦ f, 0 ≦ g, f + g ≦ 1) can be used, and the composition thereof is not particularly limited, but is preferably GaN and Al _g Ga ₁ having a g value of 0.2 or less. _{When -g} N is used, it is easy to obtain a nitride semiconductor layer with few crystal defects. The film thickness is not particularly limited, but it is a layer forming the n-electrode, so it is desirable to grow the film with a film thickness of 1 μm or more. Further, it is desirable to dope the n-type impurity at a high concentration so that the crystallinity of the nitride semiconductor is not deteriorated.
It is desirable to dope in the range of ¹⁸ / cm ³ or more and 5 × 10 ²¹ / cm ³ or less.

As the undoped GaN layer 5, similar to the above, In _f Al _g Ga _{1 -fg} N ( _{0≤f, 0≤g} , f +
g ≦ 1), and the composition thereof is not particularly limited, but is preferably GaN and Al _g Ga having a g value of 0.2 or less.
_{When 1-g} N or In _f Ga _1-f N having an f value of 0.1 or less is used, a nitride semiconductor layer with few crystal defects can be easily obtained.
Unlike the case of growing the next layer directly on the n-type contact layer 4 doped with a high concentration of impurities, the growth of the undoped GaN layer improves the crystallinity of the underlying layer. It is preferable that the multilayer film layer 6 grows easily, and if the active layer 7 is further grown on the n-type multilayer film layer, the growth becomes easy and the crystallinity becomes good. Thus, on the undoped GaN layer 3 made of an undoped nitride semiconductor layer, the n-type contact layer 4 made of a nitride semiconductor doped with a high concentration of n-type impurities, and then the undoped made of an undoped nitride semiconductor. When the GaN layer 5 is laminated and the n-type multilayer film layer 6 is further laminated, Vf tends to decrease in the case of an LED device. Note that n
When the type multilayer film layer 6 is to be undoped, undoped Ga
The N layer 5 can be omitted.

In the present invention, the above undoped G
Instead of the aN layer 5, a multilayer film layer 5a-c including an undoped lower layer 5a, an n-type impurity-doped intermediate layer 5b, and an undoped upper layer 5c described below may be used. Multilayer film layers 5a-c
Is composed of at least three layers including an undoped lower layer 5a, an n-type impurity-doped intermediate layer 5b, and an undoped upper layer 5c from the substrate side. The n-side first multilayer film layer may have a layer other than the lower layer 5a to the upper layer 5c. Further, the multilayer film layers 5a-c may be in contact with the active layer,
Other layers may be provided between the active layers. Lower layer 5a
As the nitride semiconductor constituting the ~ upper 5c, In _g A
Nitride semiconductors having various compositions represented by l _h Ga _{1 -gh} N (0 ≦ g <1, 0 ≦ h <1) can be used, and preferably those having GaN composition. Further, the layers of the multilayer film layers 5a-c may have the same composition or different compositions.

The film thickness of the multilayer film layers 5a-c is not particularly limited, but is 175 to 12000 angstroms,
It is preferably 1000 to 10000 angstroms, more preferably 2000 to 6000 angstroms. It is preferable that the thickness of the multilayer film layers 5a-c is in the above range from the viewpoint of optimization of Vf and improvement of electrostatic withstand voltage. The adjustment of the film thickness of the first multilayer film layer 5 having the film thickness in the above range is performed by appropriately adjusting the film thicknesses of the lower layer 5a, the intermediate layer 5b, and the upper layer 5c to obtain the total film thickness of the multilayer film layers 5a-c. Is preferably in the above range.

The thickness of each of the lower layer 5a, the intermediate layer 5b and the upper layer 5c constituting the multilayer film layers 5a-c is not particularly limited, but various characteristics of the device performance may be obtained depending on the position where the layers are stacked in the multilayer film layers 5a-c. Since the effect on each layer is different, pay particular attention to the characteristics of each layer that are greatly related to the device performance, fix the film thickness of any two layers, and gradually change the film thickness of the remaining one layer.
The film thickness is measured in the range of good characteristics, and the range of film thickness is specified by adjusting each layer. Each layer of the multilayer film layers 5a-c may not directly affect the electrostatic breakdown voltage, but by combining the layers to form the multilayer film layers 5a-c, various element characteristics are excellent as a whole. With
In particular, the light emission output and electrostatic withstand voltage are significantly improved.

The undoped lower layer 5a has a thickness of 100 to
10,000 Angstroms, preferably 500-80
00 angstrom, more preferably 1000-50
It is 00 angstrom. Undoped lower layer 5a
Shows that the electrostatic breakdown voltage rises as the film thickness is gradually increased, but Vf rises sharply in the vicinity of 10000 angstroms, while as the film thickness is reduced, Vf decreases, but The decrease in the withstand voltage becomes large, and if it is less than 100 Å, the yield tends to decrease with the decrease in the electrostatic withstand voltage. Further, since it is considered that the upper layer 5a improves the influence of the decrease in the crystallinity of the n-side contact layer 4 containing the n-type impurity, the upper layer 5a is grown to a film thickness such that the improvement of the crystallinity is good. Is preferred.

The thickness of the n-type impurity-doped intermediate layer 5b is
50-1000 angstrom, preferably 100-
500 angstroms, more preferably 150-40
It is 0 angstrom. The intermediate layer 5b doped with this impurity is a layer that has a sufficient carrier concentration and has a relatively large effect on the light emission output, and if this layer is not formed, the light emission output tends to be significantly reduced. Film thickness is 100
When it exceeds 0 angstrom, the emission output tends to be greatly reduced to the extent that it is difficult to obtain a product. On the other hand, if the intermediate layer 5b is thick, the electrostatic withstand voltage is good, but the thickness is 5
If the thickness is less than 0 angstrom, the electrostatic withstand voltage tends to decrease significantly, and the product cannot be sufficiently satisfied.

The thickness of the undoped upper layer 5c is 25 to 1
000 angstrom, preferably 25 to 500 angstrom, more preferably 25 to 150 angstrom. The undoped upper layer 5c is formed in contact with or closest to the active layer in the first multilayer film, and is greatly involved in the prevention of leak current.
If the film thickness of c is less than 25 Å, the leak current tends to increase. Further, as shown in FIGS. 4 (a) and 4 (b), when the film thickness of the upper layer 5c exceeds 1000 angstroms, Vf tends to increase and the electrostatic withstand voltage tends to decrease, which makes the product unsatisfactory. .

As described above, the film thickness of each of the lower layer 5a to the upper layer 5c, as described above, pays attention to the element characteristics that are easily influenced by the fluctuation of the film thickness of each layer, and further, the lower layer 5a and the intermediate layer 5b. And when the upper layer 5c is combined, all of the device characteristics are almost uniformly improved, and particularly, the emission output and the electrostatic withstand voltage are improved, and various examinations are performed to satisfy the in-house standard. By defining the film thickness, it is possible to obtain an electrostatic withstand voltage capable of achieving a good light emission output and further improvement in the reliability of the product. In addition, the combination of the film thicknesses of the respective layers of the first multilayer film layer 5 is such that the composition of the active layer changes depending on the type of emission wavelength, the electrode, the LED.
It is appropriately adjusted depending on various conditions such as the shape of the element in order to obtain the best effect. With respect to the performance associated with the combination of the film thicknesses of the respective layers, by appropriately combining the film thicknesses within the above range, it is possible to obtain a better light emission output and a better electrostatic withstand voltage than the conventional ones.

The composition of each layer constituting the above-mentioned multilayer film layers 5a-c is In _m Al _n Ga _1-mn N ( _0≤m <1, 0≤n <
The composition represented by 1) may be used, and the composition of each layer may be the same or different, preferably a composition having a small ratio of In and Al, and more preferably a layer made of GaN.

The amount of n-type impurities doped in the n-type impurity-doped intermediate layer 5b is not particularly limited, but is 3 × 10 ^18.
/ Cm ³ or more, preferably 5 × 10 ¹⁸ / cm ³ or more. The upper limit of the n-type impurities is not particularly limited, but 5 × 10 ²¹ / cm ³ or less is desirable as the limit at which the crystallinity does not deteriorate too much. When the impurity concentration of the intermediate layer of the first multilayer film layer is in the above range, it is preferable in terms of improvement of light emission output and reduction of Vf. S as an n-type impurity
i, Ge, Se, S, O, etc. Periodic Table Group IVB, VIB
A group element is selected, and preferably Si, Ge, and S are n-type impurities.

At the interface of the multilayer film layers 5a-c, both layers serve as both layers as long as they do not impair the function of each layer and element.

Next, as the active layer 7, at least In
A nitride semiconductor, preferably In _j Ga _{1 -j} N
Examples thereof include a single quantum well structure having a well layer containing (0 ≦ j <1) or a multiple quantum well structure. The order of stacking the active layers 7 may be from the well layer to the well layer, the well layer to the barrier layer, or the barrier layer to the well layer. Well, the stacking order is not particularly limited. The thickness of the well layer is adjusted to 100 angstroms or less, preferably 70 angstroms or less, and more preferably 50 angstroms or less. If it is thicker than 100 Å, it tends to be difficult to improve the output. On the other hand, the thickness of the barrier layer is 300
It is adjusted to angstroms or less, preferably 250 angstroms or less, and most preferably 200 angstroms or less.

Next, as the p-type contact layer 9 made of Mg-doped GaN, similarly to the In _f Al _g Ga
_1-fg N (0 ≦ f, 0 ≦ g, f + g ≦ 1),
The composition is not particularly limited, but preferably GaN
In that case, a nitride semiconductor layer having few crystal defects can be easily obtained, and preferable ohmic contact with the p electrode material can be easily obtained.

The p-electrode and the n-electrode used in the present invention are not particularly limited, and conventionally known and usable electrodes and the like can be used. For example, the electrodes described in the examples can be mentioned. .

[0050]

The following is an example of an embodiment of the present invention. However, the present invention is not limited to this.

[First Embodiment] A first embodiment will be described with reference to FIG. (Substrate 1) MOV the substrate 1 made of sapphire (C surface)
The substrate is set in a PE reaction vessel, the temperature of the substrate is raised to 1050 ° C. while flowing hydrogen, and the substrate is cleaned.

(Buffer layer 2) Then, the temperature is changed to 510.degree.
Then, hydrogen is used as a carrier gas, ammonia and TMG (trimethylgallium) are used as a source gas, and a buffer layer 2 made of GaN is grown on the substrate 1 to a film thickness of about 200 Å. The first to grow at this low temperature
The buffer layer 2 can be omitted depending on the type of substrate, growth method, and the like.

(Undoped GaN Layer 3) After growing the buffer layer 2, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C, TM is also used as the source gas.
G, using ammonia gas, undoped GaN layer 3 1
Grow with a film thickness of μm.

(N-type contact layer 4) Subsequently, 1050 ° C.
Then, using TMG, ammonia gas as the source gas, and silane gas as the impurity gas, an n-type contact layer made of GaN doped with Si at 3 × 10 ¹⁹ / cm ³ is grown to a thickness of 3 μm.

(Undoped GaN Layer 5) Next, only silane gas was stopped, and undoped GaN was similarly formed at 1050 ° C.
Layer 5 is grown to a thickness of 100 Angstroms.

(N-type multilayer film layer 6) Next, the temperature is set to 800.degree.
Then, using TMG, TMI, and ammonia, a second nitride semiconductor layer made of undoped In _0.03 Ga _0.97 N is grown to 25 angstroms, and then the temperature is raised. The object semiconductor layer is grown to 25 angstroms. Then, these operations are repeated to grow an n-type multilayer film having a superlattice structure in which 10 layers are alternately stacked in the second + first order with a film thickness of 500 angstrom.

(Active layer 7) Next, a barrier layer made of undoped GaN was grown to a film thickness of 200 angstroms, and subsequently the temperature was set to 800 ° C., using TMG, TMI, and ammonia to remove undoped In _0.4 Ga _0.6 N. Is grown to a film thickness of 30 Å. Then, 5 layers of barrier layers and 4 layers of well layers are alternately laminated in the order of barrier + well + barrier + well ... + Barrier to grow an active layer 7 having a multiple quantum well structure with a total film thickness of 1120 angstroms. Let

(P-type multilayer film layer 8) Next, TMG, TM
Using A, ammonia, and Cp2Mg (cyclopentadienylmagnesium), a third nitride semiconductor layer made of p-type Al _0.1 Ga _0.9 N doped with Mg at 5 × 10 ¹⁹ / cm ³ was grown to a film thickness of 25 Å. Then Cp
2Mg and TMA are stopped, and a fourth nitride semiconductor layer made of undoped GaN is grown to a film thickness of 25 Å. Then, these operations are repeated to grow the p-type multilayer film layer 8 having a thickness of 200 angstroms, which is made of a superlattice in which four layers are alternately stacked in the third + fourth order.

(P-type contact layer 9) Subsequently, 1050 ° C.
Then, using TMG, ammonia, and Cp2Mg,
A p-type contact layer 8 made of p-type GaN doped with × 10 ²⁰ / cm ³ is grown to a film thickness of 700 Å.

After completion of the reaction, the temperature was lowered to room temperature, and the wafer was further heated to 700 ° C. in a reaction vessel in a nitrogen atmosphere.
Annealing is performed at 0 ° C. to further reduce the resistance of the p-type layer.

After the annealing, 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 9, and the p-type contact layer side is etched by an RIE (reactive ion etching) apparatus. Done,
As shown in FIG. 1, the surface of the n-type contact layer 4 is exposed.

After etching, the p-type contact layer, which is the uppermost layer, has a light-transmitting p-electrode 10 containing Ni and Au having a film thickness of 200 angstroms on almost the entire surface, and Au for bonding on the p-electrode 10. The p-pad electrode 11 is formed with a film thickness of 0.5 μm. On the other hand, the n-type electrode 12 containing W and Al was formed on the surface of the n-type contact layer 4 exposed by etching to obtain an LED element.

This LED element exhibits pure green light emission of 520 nm at a forward voltage of 20 mA and Vf is 3.5 V.
However, as compared with the conventional LED device having the multiple quantum well structure, Vf was decreased by about 0.5 V, and the light emission output was more than doubled. Therefore, at 10 mA, an LED having almost the same characteristics as the conventional LED element was obtained. Further, the obtained element has an electrostatic withstand voltage that is 1.2 times or more better than that of the conventional element.

The structure of the conventional LED element is GaN.
On the first buffer layer made of undoped GaN, the second buffer layer made of undoped GaN, and n made of Si-doped GaN
-Type contact layer, active layer having the same multiple quantum well structure as in Example 1, single Mg-doped Al _0.1 Ga _0.9 N layer,
A p-type contact layer made of Mg-doped GaN is sequentially stacked.

Example 2 In Example 1, when growing the n-type multilayer film layer 6, only the first nitride semiconductor layer was
An LED element was prepared in the same manner except that Si was grown as 1 × 10 ¹⁸ / cm ³ -doped GaN. Obtained L
The ED element has good element characteristics which are almost the same as those of the first embodiment.

[Embodiment 3] In Embodiment 1, when the n-type multilayer film layer 6 is grown, the second nitride semiconductor layer is an In _0.03 Ga _0.97 layer doped with Si at 1 × 10 ¹⁸ / cm ^3. ,
An LED element was manufactured in the same manner except that the first nitride semiconductor layer was GaN doped with Si at 5 × 10 ¹⁸ / cm ³ . The obtained LED element showed excellent characteristics with Vf of 3.4 V at 20 mA and an output of 1.5 times or more as compared with the conventional one. Further, the electrostatic breakdown voltage is as good as that of the first embodiment.

[Embodiment 4] In Embodiment 1, when the p-type multilayer film layer 8 is grown, a p-type GaN layer doped with Mg of 1 × 10 ¹⁹ / cm ³ is grown on the fourth nitride semiconductor layer. Example 1 was repeated except that the LED element was manufactured in the same manner.
As a result, an LED element having characteristics substantially equivalent to the above was obtained.

[0068] In Example 5 Example 1, in growing the p-type multi-film layer 8, the third nitride semiconductor layer made of undoped Al _0.1 Ga _{0 .9} N and 25 Å, undoped GaN An LED element was manufactured in the same manner except that two fourth layers each having a thickness of 100 angstroms were alternately laminated with the fourth nitride semiconductor layer having a thickness of 25 angstroms. An LED device having the above was obtained.

[Embodiment 6] An LED is prepared in the same manner as in Embodiment 1 except that the total number of multilayer films 5a-c is changed to the undoped GaN layer 5 and the following layers are changed as follows.
Manufacture the device.

(N-side contact layer 4) Subsequently, 1050 ° C.
Then, similarly, using TMG, ammonia gas as the source gas, and silane gas as the impurity gas, the n-side contact layer 4 made of GaN doped with Si at 6 × 10 ¹⁸ / cm ³ is 2.25 μm.
Grow with a film thickness of m.

(Multilayer Film Layers 5a-c) Next, the silane gas alone was stopped, and the lower layer 5a made of undoped GaN was grown to a thickness of 2000 angstroms at 1050 ° C. using TMG and ammonia gas, and subsequently at the same temperature. Silane gas was added and Si was doped at 6 × 10 ¹⁸ / cm ³ Ga
The intermediate layer 5b made of N is grown to a film thickness of 300 angstroms, and then only the silane gas is stopped, and the upper layer 5c made of undoped GaN is grown to a film thickness of 50 angstroms at the same temperature. Thickness 235
A 0 angstrom first multilayer film layer 5 is grown.

(N-type multilayer film layer 6) Next, at the same temperature,
The first nitride semiconductor layer made of undoped GaN is 40
Angstrom growth is performed, then the temperature is set to 800 ° C., TMG, TMI, and ammonia are used, and undoped I
The first nitride semiconductor layer made of n _0.02 Ga _0.98 N
Grow angstroms. Then, these operations are repeated, and 10 layers are alternately laminated in the first + second order,
Finally, an n-type multilayer film layer 6 made of a multilayer film having a superlattice structure in which a first nitride semiconductor layer made of GaN is grown to 40 angstroms is grown to a film thickness of 640 angstroms.

(P-type multilayer film layer 8) Next, the temperature is 1050 ° C.
At this time, TMG, TMA, ammonia, and Cp2Mg (cyclopentadienylmagnesium) are used, and Mg is added to 5 × 10 ¹⁹
/ Cm ³ -doped p-type Al _0.2 Ga _0.8 N third nitride semiconductor layer was grown to a film thickness of 40 angstrom, and then the temperature was set to 800 ° C. and TMG, TMI, ammonia, and Cp 2 Mg were used to form Mg. A fourth nitride semiconductor layer of In _0.02 Ga _0.98 N doped with 5 × 10 ¹⁹ / cm ³ is grown to a film thickness of 25 Å. Then, these operations are repeated, and 5 layers are alternately laminated in the order of 3 + 4, and finally, a third nitride semiconductor layer is grown to a thickness of 40 angstroms. The mold multilayer film layer 8 is grown to a film thickness of 365 angstrom.

The obtained LED element showed favorable light emission output and Vf almost in the same manner as in Example 1, and further, a voltage was gradually applied in the opposite direction from each electrode of the n layer and the p layer of the LED element to obtain electrostatic properties. When the breakdown voltage was measured, it was 1.5 times or more that of the conventional element described in Example 1, and the static breakdown voltage was better than that of Example 1.

[0075]

According to the present invention, the reliability of the device is improved and the range of application to various applied products can be expanded. Therefore, the light emission output can be further improved, and the electrostatic breakdown voltage with a low Vf is excellent. A nitride semiconductor device can be provided.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing the structure of an LED element according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Sapphire substrate 2 ... Buffer layer 3 ... Undoped GaN layer 4 ... Si-doped GaN n-type contact layer 5 ... Undoped GaN layer 6 ... n-type multilayer film layer 7 ... Active layer 8 ... p-type multilayer film layer 9 ... Mg-doped GaN p-type contact layer 10 ... Full surface electrode 11 ... p electrode 12 ... n electrode

─────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-10-242512 (JP, A) JP-A-8-23124 (JP, A) JP-A-9-116234 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) H01L 33/00 H01L 31/04 H01L 31/10 H01S 5/00-5/50 JISST file (JOIS)

Claims (7)

(57) [Claims] 1. A nitride semiconductor device having an active layer between an n-type nitride semiconductor and a p-type nitride semiconductor, wherein the n-type nitride semiconductor is Al _g Ga _{1 -g} N (0 ≦ g ≤
0.2) n-type contact layer, GaN layer and In
_An n-type multilayer film layer in which _p Ga _1-p N (0 <p <1) layers are stacked, an undoped GaN lower layer and n between the n-type contact layer and the n-type multilayer film layer. A nitride semiconductor device, comprising: an n-side first multilayer film layer having an intermediate layer made of GaN doped with a type impurity. 2. The nitride semiconductor device according to claim 1, wherein the n-side first multilayer film layer further includes an upper layer made of an undoped nitride semiconductor. 3. The nitride semiconductor device according to claim 1, wherein the lower layer made of undoped GaN has a film thickness of 100 to 10000Å. 4. The n-type multilayer film layer is undoped GaN.
The nitride semiconductor device according to claim 1, wherein the layer and the undoped In _p Ga _1-p N (0 <p <1) layer are stacked. 5. The p-type nitride semiconductor is Al _x Ga _{1 -x.}
5. A p-type multilayer film layer having a superlattice structure formed by stacking N (0 <x <1) and In _y Ga _1-y N (0 ≦ y <1), in any one of claims 1 to 4. 1. The nitride semiconductor device according to one. 6. The nitride semiconductor device according to claim 5, wherein the number of nitride semiconductor layers forming the p-type multilayer film layer is smaller than the number of nitride semiconductor layers forming the n-type multilayer film layer. . 7. The nitride semiconductor device according to claim 6, wherein the p-type multilayer film layer is modulation-doped.