JP4085782B2 - Nitride semiconductor device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a light emitting diode (LED), a laser diode (LD), a light emitting element such as a solar cell or a photosensor, a light receiving element, or a nitride semiconductor (for example, In _X ) used in an electronic device such as a transistor or a power device. Al _Y Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1).
[0002]
[Prior art]
Nitride semiconductors have been put to practical use in various light sources such as full-color LED displays, traffic signal lights, and image scanner light sources as materials for high-intensity blue LEDs and pure green LEDs. These LED elements are basically a sapphire substrate buffer layer made of GaN, an n-type contact layer made of Si-doped GaN, an InGaN single quantum well structure (SQW: Single-Quantum-Well) or an InGaN type. A multi-quantum well structure (MQW: Multi-Quantum-Well) active layer, a p-type cladding layer made of Mg-doped AlGaN, and a p-type contact layer made of Mg-doped GaN are sequentially stacked. .
[0003]
At 20 mA, a blue LED with a wavelength of 450 nm has a light output of 2.5 mW in the single quantum well structure, an external quantum efficiency of 5%, a light output of 5 mW in the multiple quantum well structure, and an external quantum effect of 9.1%. The green LED of 520 nm has very excellent characteristics such as a light emission output of 2.2 mW in a single quantum well structure, an external quantum efficiency of 4.3%, a light emission output of 3 mW in a multiple quantum well structure, and an external quantum effect of 6.3%. Show.
[0004]
As described above, the LED element disclosed by the above-mentioned applicant has a high output, can be applied to practical use, and is applied to various products such as signals.
[0005]
[Problems to be solved by the invention]
However, at the present time when an LED element capable of reducing power consumption without lowering the light emission output is desired in accordance with recent energy savings, the above LED element is not sufficient. The LED element has a forward voltage (V _f ) of nearly 3.6 V at 20 mA, and further reduction is desired.
[0006]
Accordingly, an object of the present invention is to solve the above problems and provide a nitride semiconductor device having excellent device characteristics.
[0007]
[Means for Solving the Problems]
That is, the nitride semiconductor device of the present invention can be achieved by the following configurations (1) to (8).
(1) In a nitride semiconductor device having at least an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer on a substrate in order, the active layer is a well layer including a nitride semiconductor containing In And a barrier layer comprising a nitride semiconductor, the barrier layer comprising a last barrier layer formed closest to the p-type nitride semiconductor layer in the active layer, and the last barrier layer And a modulation-doped barrier layer formed on the n-type nitride semiconductor layer side, the last barrier layer is a layer not intentionally doped with impurities, and the modulation-doped barrier layer includes an n-type An n-type impurity high-concentration layer doped with impurities, and an n-type impurity low-concentration layer formed adjacent to the n-type impurity high-concentration layer and having a lower n-type impurity concentration than the n-type impurity high-concentration layer On the last barrier layer It is characterized by having a p-type multi-film layer of the super lattice structure. Thereby, a nitride semiconductor device capable of reducing the forward voltage without deteriorating device characteristics can be provided.
As a more specific nitride semiconductor device of the present invention,
(2) The n-type impurity low concentration layer is not intentionally doped with impurities,
(3) The p-side nitride semiconductor layer includes a p-type contact layer.
[0008]
(4) The modulation doped barrier layer is a lower layer made of a nitride semiconductor not intentionally doped with impurities, an intermediate layer made of a nitride semiconductor doped with n-type impurities, and intentionally doped with impurities. At least three upper layers made of non-nitride semiconductors are sequentially stacked. As a result, it is possible to minimize the diffusion of impurities into the well layer in contact with the barrier layer and to suppress the deterioration of the crystallinity of the well layer.
[0009]
(5) The n-type impurity is at least one of Si, Ge, and Sn.
(6) The barrier layer, said has an undoped barrier layer of undoped another intentional impurities the last barrier layer, in order from the n-type nitride semiconductor layer side, and the modulation-doped barrier layer, Having an undoped barrier layer and the last barrier layer;
(7) The impurity concentration difference between the n-type impurity high concentration layer and the n-type impurity low concentration layer of the modulation doped barrier layer is one digit or more.
(8) The film thickness of the n-type impurity high concentration layer is 10 to 60 mm.
It is characterized by that.
[0010]
In the present invention, an undoped nitride semiconductor layer refers to a nitride semiconductor layer that is not intentionally doped with impurities. For example, impurities contained in raw materials, contamination in the reaction apparatus, and other layers intentionally doped with impurities In the present invention, a layer in which impurities are mixed due to unintended expansion from the layer and a layer that can be regarded as substantially undoped due to a small amount of doping (for example, resistivity of 3 × 10 ⁻¹ Ω · cm or more) are also defined as undoped in the present invention.
[0011]
In the present invention, the fact that the n-type impurity is contained in the nitride semiconductor layer may be indicated as addition or dope.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
As a result of various experiments, the inventor of the present application has found a nitride semiconductor capable of reducing the forward voltage while minimizing a decrease in light emission output, and has achieved the present invention.
[0013]
Since the multiple quantum well structure has a large film thickness, an undoped active layer having no impurities has a high resistance. If an n-type or p-type impurity is added to the active layer, the resistance can be lowered.
[0014]
However, if the impurity concentration is too high, the crystallinity of the layer or the layer in contact with the layer is deteriorated, and the light emission output tends to be reduced.
[0015]
Therefore, this time, when doping an n-type impurity into a single layer of a well layer or a barrier layer in an active layer, the element can be reduced in the forward voltage without deteriorating the active layer by doping in modulation. A nitride semiconductor device having excellent characteristics is formed.
[0016]
FIG. 1 is a schematic cross-sectional view of an element structure of a nitride semiconductor element, which is an embodiment of the present invention. Hereinafter, the nitride semiconductor device of the present embodiment will be described in detail.
[0017]
FIG. 1 shows an n-type comprising 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 lower layer, an n-type impurity doped intermediate layer, and an undoped upper layer. A first multilayer film layer 5; an n-type second multilayer film layer 6 comprising third and fourth nitride semiconductor layers; an active layer 7 having a multiple quantum well structure; a p-type multilayer film layer 8 containing p-type impurities; A p-type contact layer made of n-type impurity doped GaN is sequentially stacked. Further, an n-electrode 11 is formed on the n-type contact layer 4 and a p-electrode 10 is formed on the p-type contact layer 9.
[0018]
(Active layer 7)
In the present invention, the active layer 7 has a quantum well structure including a nitride semiconductor having In in the well layer 7b, and has a multi-quantum well structure having a multilayer structure in which the well layer 7b and the barrier layer 7a are sequentially stacked. is there. The order of lamination of the well layer 7b and the barrier layer 7a is not particularly limited, and is laminated from the well layer 7b and ends with the well layer 7b, from the well layer 7b and ends with the barrier layer 7a, and from the barrier layer 7a. It may end with the barrier layer 7a, or may be stacked from the barrier layer 7a and end with the well layer 7b. The thickness of the active layer 7 is not particularly limited, and the total thickness of the active layer is adjusted by adjusting the number and order of the well layers 7b and the barrier layers 7a in consideration of the desired wavelength of the LED element and the like. To do. Specifically, it is 200 to 8000 angstrom, preferably 500 to 6000 angstrom. A total film thickness of the active layer 7 within the above range is preferable in terms of light emission output and time required for crystal growth of the active layer 7.
[0019]
(Well layer)
The well layer contains a nitride semiconductor having In. The single thickness of the well layer is adjusted to 100 angstroms or less, preferably 70 angstroms or less, more preferably 50 angstroms or less. The lower limit of the thickness of the well layer is not particularly limited, but it is 1 atomic layer or more, preferably 10 angstroms or more. It is preferable that the single film thickness of the well layer is in the above range from the viewpoint of improving the light emission output and reducing the half width of the light emission spectrum.
[0020]
(Barrier layer 7a)
On the other hand, the single film thickness of the barrier layer 7a is 30 to 500 angstroms, preferably 50 to 300 angstroms. When the barrier layer 7a is in the above range, the photoelectric conversion efficiency is improved, and low V _f and low leakage current are preferable. The barrier layer 7a is selected from a nitride semiconductor having a larger band gap energy than the well layer 7b, preferably In _Y Ga _1-Y N (0 ≦ Y <1, X> Y) or Al _Z Ga _1-Z. N (0 <Z <0.5). However, the well layer 7b and the barrier layer 7a can be made of InAlN.
[0021]
(N-type impurities)
In the present invention, the n-type impurity doped into the active layer 7 may be a group IV or group VI element such as Si, Ge, Sn, S, O, Ti, Zr. Si, Ge, and Sn are preferably used, and Si is more preferably used.
[0022]
(Modulation dope)
When the active layer 7 is doped with an n-type impurity, it is modulation-doped in a single layer of the well layer 7b or the barrier layer 7a. Modulation doping is a method in which the impurity concentration of one layer is low, preferably undoped in a state in which no impurity is doped, and the other side of the layer is highly doped, and the threshold voltage, forward voltage, etc. are reduced. be able to. This is because a layer having a low impurity concentration is present in the multilayer film layer, so that the mobility of the layer is increased, and a layer having a high impurity concentration is also present at the same time. By being able to form a layer. In other words, the presence of a high mobility layer with a low impurity concentration and a layer with a high impurity concentration and a high carrier concentration at the same time makes a layer with a high carrier concentration and high mobility a cladding layer. It is presumed that the voltage and forward voltage will decrease. In the case of modulation doping, the impurity concentration difference is preferably one digit or more.
[0023]
In the present invention, when the well layer 7b is doped with an n-type impurity, the single layer preferably has a two-layer structure of an n-type impurity doped layer and an undoped layer. The doping amount (concentration) of the n-type impurity is 1 × 10 ¹⁷ / cm ³ to 1 × 10 ¹⁹ / cm ³ , preferably 6 × 10 ¹⁷ / cm ^{3 to} 7 × 10 ¹⁸ / cm ³ , more preferably 9 ×. 10 ¹⁷ / cm ^{3 to} 5 × 10 ¹⁸ / cm ³ . The thickness of the doped layer is 10 angstroms to 50 angstroms, preferably 10 angstroms to 30 angstroms, more preferably 10 angstroms to 20 angstroms.
[0024]
On the other hand, when the barrier layer 7a is doped with n-type impurities in the present invention, the lower layer 7a- (1) made of undoped nitride semiconductor in a single layer, and the intermediate layer made of nitride semiconductor doped with n-type impurities It is preferable to have a three-layer structure in which at least three layers of 7a- (2) and an upper layer 7a- (3) made of an undoped nitride semiconductor are sequentially stacked. The doping amount (concentration) of the n-type impurity is 1 × 10 ¹⁷ / cm ³ to 1 × 10 ¹⁹ / cm ³ , preferably 6 × 10 ¹⁷ / cm ^{3 to} 7 × 10 ¹⁸ / cm ³ , more preferably 9 ×. 10 ¹⁷ / cm ^{3 to} 5 × 10 ¹⁸ / cm ³ . The thickness of the doped layer is 10 angstroms to 100 angstroms, preferably 10 angstroms to 60 angstroms, more preferably 10 angstroms to 30 angstroms. This range is preferable in terms of obtaining good crystallinity and low resistivity.
[0025]
【Example】
Examples of the present invention will be described below. In addition, this invention is not limited only to the Example shown below.
[0026]
[Example 1]
Based on FIG. 1, a manufacturing method of Example 1 of the element of the present invention will be described.
[0027]
(Substrate 1)
The substrate 1 made of sapphire (C-plane) is set in a MOVPE reaction vessel, and the inside of the vessel is sufficiently replaced with hydrogen, and then the temperature of the substrate is raised to 1050 ° C. while flowing hydrogen to clean the substrate. In addition to the sapphire C surface, the substrate 1 is a sapphire substrate whose main surface is the R surface and the A surface, an insulating substrate such as spinel (MgAl ₂ O ₄ ), SiC (including 6H, 4H, and 3C), Si, A semiconductor substrate such as ZnO, GaAs, or GaN can be used.
[0028]
(Buffer layer 2)
Subsequently, the temperature is lowered to 510 ° C., hydrogen is used as a carrier gas, ammonia and TMG (trimethyl gallium) are used as a source gas, and a buffer layer 2 made of GaN is grown to a thickness of about 200 Å on the substrate. The buffer layer 2 can be omitted depending on the type of substrate and the growth method. The buffer layer 2 can also be made of AlGaN with a small Al ratio.
[0029]
(Undoped GaN layer 3)
After growth of the buffer layer 2, only TMG is stopped and the temperature is raised to 1050 ° C. When the temperature reaches 1050 ° C., TMG and ammonia gas are similarly used as the source gas, and the undoped GaN layer 3 is grown to a thickness of 1.5 μm.
[0030]
(N-type contact layer 4)
Subsequently, at 1050 ° C., an n-type contact layer 4 made of GaN doped with Si at 5 × 10 ¹⁸ / cm ³ is grown to a thickness of 2.165 μm, using TMG as the source gas and silane gas as the impurity gas. Let
[0031]
(N-type first multilayer film layer 5)
Next, the silane gas alone is stopped, TMG and ammonia gas are used at 1050 ° C., and a lower layer made of undoped GaN is grown to a thickness of 3000 angstroms. Subsequently, silane gas is added at the same temperature to add Si to 4 × 10 ¹⁸ / An intermediate layer made of GaN doped with cm ³ is grown to a thickness of 300 Å, and then only the silane gas is stopped, and an upper layer made of undoped GaN is grown to a thickness of 50 Å at the same temperature, and consists of three layers. An n-type first multilayer film layer 5 having a layer thickness of 3350 angstroms is grown.
[0032]
(N-type second multilayer layer 6)
Next, a nitride semiconductor layer made of undoped GaN is grown at 40 Å at the same temperature, then the temperature is set to 800 ° C., and TMG, TMI, and ammonia are used to form a nitride semiconductor layer made of undoped In _0.3 Ga _0.7 N. For 20 angstroms. By repeating these operations, an n-type second multilayer film layer 6 made of a multilayer film having a superlattice structure in which 10 layers are alternately stacked is grown to a thickness of 600 angstroms.
[0033]
(Active layer 7)
Next, a lower layer 7a- (1) made of undoped GaN is grown to a thickness of 120 Å using TMG and ammonia. Subsequently, silane gas is added at the same temperature, and an intermediate layer 7a- (2) made of GaN doped with Si at 1 × 10 ¹⁸ / cm ³ is grown to a thickness of 10 angstroms. The upper layer 7a- (3) made of undoped GaN is grown at a temperature of 120 angstroms at a temperature, and such a three-layer barrier layer 7a having a total thickness of 250 angstroms is grown.
[0034]
Next, a well layer 7b made of undoped In _0.3 Ga _0.7 N is grown to a thickness of 30 Å using TMG, TMI, and ammonia at the same temperature. By repeating these operations, six layers of Si-doped three-layer barrier layers 7a and undoped well layers 7b are alternately stacked. Finally, an undoped barrier layer 7a 'is laminated with a film thickness of 250 angstroms, and an active layer made of a multiple quantum well structure with a total of 13 layers and a total film thickness of 1930 angstroms is grown. As a result, the barrier layer has a three-layer structure in which the sixth to sixth layers are Si-doped.
[0035]
(P-type multilayer film layer 8)
Next, a nitride semiconductor layer made of p-type Al _0.2 Ga _0.8 N doped with Mg at 5 × 10 ¹⁹ / cm ³ using TMG, TMA, ammonia, Cp ₂ Mg (cyclopentanedienylmagnesium) at a temperature of 1050 ° C. Of In _0.02 Ga _0.98 N doped with 5 × 10 ¹⁹ / cm ^{3 of} Mg using TMG, TMI, ammonia, Cp ₂ Mg at a temperature of 800 ° C. A semiconductor layer is grown to a thickness of 25 angstroms. By repeating these operations, five p-type AIGaN layers and five p-type InGaN layers are alternately laminated to form a p-type multilayer film layer 8 composed of a multilayer film having a superlattice structure with a total number of 10 layers and a total film thickness of 325 angstroms. Grow.
[0036]
(P-type contact layer 9)
Subsequently, at 1050 ° C., a p-type contact layer 9 made of p-type GaN doped with Mg at 1 × 10 ²⁰ / cm ³ is grown to a thickness of 1200 Å using TMG, ammonia, and Cp ₂ Mg.
[0037]
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.
[0038]
After annealing, the wafer is taken out from the reaction vessel, a mask having a predetermined shape is formed on the surface of the uppermost p-type contact layer, and etching is performed from the p-type contact layer 9 side with an RIE (reactive ion etching) apparatus. As shown in FIG. 1, the surface of the n-type contact layer 4 is exposed.
[0039]
After exposing the surface of each pn semiconductor by etching, each electrode is formed by sputtering.
[0040]
The LED element thus obtained exhibited blue light emission of 463 nm at 20 mA, V _f was 3.36 V, and light emission output was 6.5 mW.
[0041]
[Example 2]
When the active layer 7 is formed, an LED element is formed in the same manner as in Example 1 except that the Si-doped barrier layer 7a has a three-layer structure, and seven of the seven layers have a three-layer structure doped with Si. did.
[0042]
The LED element thus obtained exhibited blue light emission of 468 nm at 20 mA, V _f was 3.4 V, and light emission output was 6.5 mW.
[0043]
[Example 3]
When forming the active layer 7, the three-layered barrier layer 7a doped with Si has a three-layered structure of Si doped from the bottom to the third of the seven layers, and the upper four layers are undoped barrier layers 7a ′. The LED element was formed in the same manner as in Example 1 except that.
[0044]
The LED element thus obtained showed blue emission of 471 nm at 20 mA, V _f was 3.45 V, and the light emission output was 6.69 mW.
[0045]
[Example 4]
When the barrier layer 7a of the active layer 7 is formed, a lower layer 7a- (1) made of undoped GaN is grown to a thickness of 116.6 Å using TMG and ammonia, and then silane gas is added at the same temperature. An intermediate layer 7a- (2) made of GaN doped with Si at 1 × 10 ¹⁸ / cm ^{3 is formed} to a thickness of 16.8 angstrom, and then only the silane gas is stopped, and the upper layer 7a- made of undoped GaN at the same temperature. An LED element was formed in the same manner as in Example 1 except that (3) was grown to a thickness of 116.6 angstroms and a barrier layer 7a having a total film thickness of 250 angstroms consisting of these three layers was grown.
[0046]
The LED element thus obtained emitted blue light of 459 nm at 20 mA, V _f was 3.27 V, and the light emission output was 6.03 mW.
[0047]
[Example 5]
When the barrier layer 7a of the active layer 7 is formed, a lower layer 7a- (1) made of undoped GaN is grown to a thickness of 141.6 angstroms using TMG and ammonia, and then silane gas is added at the same temperature. An intermediate layer 7a- (2) made of GaN doped with Si at 1 × 10 ¹⁸ / cm ³ is grown to a thickness of 16.8 angstrom, and then only the silane gas is stopped and an upper layer made of undoped GaN at the same temperature. 7a- (3) was grown to a thickness of 141.6 angstroms, and an LED element was formed in the same manner as in Example 1 except that such a three-layer barrier layer 7a having a total thickness of 300 angstroms was grown. .
[0048]
The LED element thus obtained showed blue light emission of 459 nm at 20 mA, V _f was 3.40 V, and the light emission output was 5.93 mW.
[0049]
[Example 6]
When the barrier layer 7a of the active layer 7 is formed, a lower layer 7a- (1) made of undoped GaN using TMG and ammonia is grown to a film thickness of 166.6 angstrom, and then silane gas is added at the same temperature. An intermediate layer 7a- (2) made of GaN doped with Si at 1 × 10 ¹⁸ / cm ³ is grown to a thickness of 16.8 angstrom, and then only the silane gas is stopped and an upper layer made of undoped GaN at the same temperature. 7a- (3) was grown to a thickness of 166.6 angstroms, and an LED element was formed in the same manner as in Example 1 except that such a three-layer barrier layer 7a having a total film thickness of 350 angstroms was grown. .
[0050]
The LED element thus obtained emitted blue light of 457 nm at 20 mA, V _f was 3.45 V, and the light emission output was 6.41 mW.
[0051]
[Example 7]
When the barrier layer 7a of the active layer 7 is formed, a lower layer 7a- (1) made of undoped GaN is grown to a thickness of 191.6 Å using TMG and ammonia, and then silane gas is added at the same temperature. An intermediate layer 7a- (2) made of GaN doped with Si at 1 × 10 ¹⁸ / cm ³ is grown to a thickness of 16.8 angstrom, and then only the silane gas is stopped and an upper layer made of undoped GaN at the same temperature. 7a- (3) was grown to a thickness of 191.6 angstroms, and an LED element was formed in the same manner as in Example 1 except that such a three-layer barrier layer 7a having a total thickness of 400 angstroms was grown. .
[0052]
The LED element thus obtained showed blue light emission of 459 nm at 20 mA, V _f was 3.50 V, and the light emission output was 6.21 mW.
[0053]
[Example 8]
When the barrier layer 7a of the active layer 7 is formed, a lower layer 7a- (1) made of undoped GaN is grown to a thickness of 241.6 angstrom using TMG and ammonia, and then silane gas is added at the same temperature. An intermediate layer 7a- (2) made of GaN doped with Si at 1 × 10 ¹⁸ / cm ³ is grown to a thickness of 16.8 angstrom, and then only the silane gas is stopped and an upper layer made of undoped GaN at the same temperature. An LED element was formed in the same manner as in Example 1 except that 7a- (3) was grown to a thickness of 241.6 angstroms and a barrier layer having a total thickness of 500 angstroms consisting of these three layers was grown.
[0054]
The LED element thus obtained exhibited blue light emission of 462 nm at 20 mA, V _f was 3.55 V, and the light emission output was 6.31 mW.
[0055]
【The invention's effect】
As described above, in a nitride semiconductor device having at least an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer on a substrate in order, the active layer includes a nitride semiconductor having In in a well layer. The forward voltage can be reduced without causing deterioration of device characteristics by modulating and doping an n-type impurity in a single layer of the well layer or the barrier layer. Among the barrier layers, there was no particular difference due to the presence or absence of doping in the last laminated last barrier layer, but considering that the last barrier layer is the base of the p-type multilayer film layer and the p-type contact layer The last barrier layer is preferably undoped.
[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.
FIG. 2 is a schematic cross-sectional view showing a structure of an active layer of an LED element according to an embodiment of the present invention.
DESCRIPTION OF SYMBOLS 1 ... Sapphire substrate 2 ... Buffer layer 3 ... Undoped GaN layer 4 ... n-type contact layer 5 ... n-type 1st multilayer film layer 6 ... n-type 2nd multilayer film layer 7 ... active layer 7a ... n-type doped barrier layer 7a- (1) ... undoped lower barrier layer 7a- (2) ... n-type doped intermediate barrier layer 7a- (3) ... undoped Upper barrier layer 7a '... undoped barrier layer 7b ... undoped well layer 8 ... p-type multilayer film layer 9 ... p-type contact layer 10 ... p electrode 11 ... n electrode

Claims (8)

In a nitride semiconductor device having at least an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer in this order on a substrate,
The active layer has a multiple quantum well structure having a well layer containing a nitride semiconductor containing In and a barrier layer containing a nitride semiconductor,
The barrier layer has a last barrier layer formed closest to the p-type nitride semiconductor layer in the active layer, and a modulation-doped barrier layer formed closer to the n-type nitride semiconductor layer than the last barrier layer ,
The last barrier layer is a layer that is not intentionally doped with impurities,
The modulation doped barrier layer includes an n-type impurity high concentration layer doped with an n-type impurity and an n-type impurity high concentration layer formed adjacent to the n-type impurity high concentration layer and having a lower n-type impurity concentration. an n-type impurity low concentration layer ,
A nitride semiconductor device comprising a p-type multilayer film having a superlattice structure on the last barrier layer .   The nitride semiconductor device according to claim 1, wherein the n-type impurity low concentration layer is intentionally not doped with an impurity.   The nitride semiconductor device according to claim 1, wherein the p-side nitride semiconductor layer includes a p-type contact layer.   The modulation doped barrier layer includes a lower layer made of a nitride semiconductor not intentionally doped with an impurity, an intermediate layer made of a nitride semiconductor doped with an n-type impurity, and a nitridation not intentionally doped with an impurity. 4. The nitride semiconductor device according to claim 1, wherein at least three upper layers made of a physical semiconductor are laminated in order. 5.   The nitride semiconductor element according to claim 1, wherein the n-type impurity is at least one of Si, Ge, and Sn. Said barrier layer, said has an undoped barrier layer of undoped another intentional impurities the last barrier layer, in order from the n-type nitride semiconductor layer side, and the modulation-doped barrier layer, an undoped barrier The nitride semiconductor device according to claim 1, further comprising a layer and the last barrier layer.   7. The nitride according to claim 1, wherein an impurity concentration difference between the n-type impurity high-concentration layer and the n-type impurity low-concentration layer of the modulation doped barrier layer is one digit or more. Semiconductor element.   The nitride semiconductor device according to claim 1, wherein the n-type impurity high concentration layer has a thickness of 10 to 60 mm.

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