JPH10270755A - Nitride semiconductor device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain superior ohmic contact of low Mg concentration by forming a positive electrode, containing at least Ru and Ni, on the surface of a p-type nitride semiconductor layer doped with p-type impurities. SOLUTION: A buffer layer 2, an n-side contact layer 3, an anti-crack layer 4, an n-side clad layer 5, an n-side optical guide layer 6, an active layer 7, a p-type cap layer 8, a p-side optical guide layer 9 and a p-side clad layer 10 are laminated on a sapphire substrate 1 in this order, and after this, a p-side contact layer 11 comprising p-type GaN doped with Mg is formed, and then a positive electrode 20 comprising an alloy containing Ru and Ni by 50% each is formed on the entire surface of the uppermost layer. When Mg concentration becomes 1×10<18> cm<3> , superior ohmic is obtained with Ru/Ni, and by using such a positive electrode containing Ru and Ni as this, superior ohmic contact of low Mg concentration is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light emitting diode (LE).
D), a light emitting element such as a laser diode (LD), a light receiving element such as a solar cell or an optical sensor, or a nitride semiconductor (In _X Al _Y ) used for an electronic device such as a transistor.
Ga _1-XY N, 0 ≦ X, 0 ≦ Y, X + Y ≦ 1).

[0002]

2. Description of the Related Art Nitride semiconductors have just recently been put to practical use in full-color LED displays, traffic signals and the like as materials for high-brightness blue LEDs and pure green LEDs. LEDs used in these various devices include an active layer made of InGaN having a single quantum well structure (SQW: Single-Quantum-Well) between an n-type nitride semiconductor layer and a p-type nitride semiconductor layer. It has a double heterostructure. Wavelengths such as blue and green are determined by increasing or decreasing the In composition ratio of the InGaN active layer.

In addition, the present applicant has recently published a laser oscillation of 410 nm at room temperature under pulse current using this material (for example, Appl. Phys. Lett., Vol. 69, No. 1).
0, 2 Sep. 1996, p. 1477-1479). This laser device has a structure in which an n-type nitride semiconductor layer, an active layer, and a p-type nitride semiconductor layer are sequentially formed on a sapphire A surface, and a ridge stripe is formed in part of the p-type nitride semiconductor layer. For example, a pulse current (pulse width 1 μs, pulse cycle 1
ms, duty ratio 0.1%) and threshold current 187m
A: A laser beam of 410 nm is oscillated at a threshold current density of 3 kA / cm ² .

Each of these light-emitting elements has a double hetero structure in which an active layer emitting light is sandwiched between a p-type layer and an n-type layer, and the uppermost p-layer is made of a Ni alloy. A positive electrode is provided. The positive electrode of the Ni alloy has good ohmic contact with the p-type nitride semiconductor and has excellent adhesiveness with the nitride semiconductor, and is currently a useful electrode.

In addition to the Ni alloy positive electrode, a p-type nitride semiconductor electrode material has been proposed. For example, JP-A-8-3
No. 2115 discloses an electrode containing a metal nitride and a metal hydride (hydrogen storage metal). Specifically, Pd is used for a metal hydride, Ti is used for a metal nitride,
Hf, Nb, etc. are shown. Also, Japanese Patent Application Laid-Open No. 7-249
No. 797 discloses an electrode made of Cr and Au. JP-A-5-315647 discloses Ag, A
It is shown that simple metals or alloys such as u, Pt, Ir, Pd, and Rh are used.

[0006]

It is known that a p-type nitride semiconductor can be obtained by techniques such as annealing and electron beam irradiation. However, even if a p-type nitride semiconductor is obtained, its resistivity is several tens Ω. -Very high from cm to several hundred ohm-cm. Moreover, even if p-type impurities are doped at a high concentration,
Since the type impurity is only about 1/100 of the doping amount and the actual carrier concentration is only 10 ¹⁷ to 10 ¹⁸ / cm ³ ,
There are few metals that can obtain good ohmic contact with the type nitride semiconductor. Further, when a p-type impurity is doped at a high concentration in the nitride semiconductor, the crystallinity of the p-type nitride semiconductor is deteriorated, the electric characteristics are also deteriorated, and there is a disadvantage that it is still difficult to obtain ohmic.

If a p-type nitride semiconductor having a low impurity concentration and a preferable ohmic can be obtained, a p-type nitride semiconductor serving as a contact layer as a current injection layer has good crystallinity, so that a long-life element can be realized. Be expected. Accordingly, it is an object of the present invention to provide a nitride semiconductor device having a positive electrode capable of stably obtaining a favorable ohmic contact with a p-type nitride semiconductor even in a range where the doping amount of a p-type impurity is small. is there.

[0008]

The nitride semiconductor device of the present invention is characterized in that a positive electrode containing at least Ru and Ni is formed on the surface of a p-type nitride semiconductor layer doped with a p-type impurity. Features.

The p-type nitride semiconductor on which the positive electrode is formed is
It is characterized in that Mg is doped at 5 × 10 ¹⁷ / cm ³ or more and 2 × 10 ²⁰ / cm ³ or less. Mg is 5 × 10 ¹⁷ / cm
³ small, no sufficient carrier concentration is obtained than tends it is difficult to obtain an ohmic contact, 2 × 10 ²⁰
If it is more than / cm ^3, the crystallinity of the p-type nitride semiconductor layer deteriorates, and the device life tends to be shortened.

[0010] Further, the semiconductor device is characterized in that the thickness of the p-type nitride semiconductor layer is 400 Å or less.
By reducing the thickness of the p-type nitride semiconductor layer forming the positive electrode, the series bulk resistance of the p-type nitride semiconductor itself is reduced, and the current is easily spread uniformly in the contact layer.

[0011]

FIG. 1 is a diagram showing current-voltage characteristics of an electrode formed on p-type GaN. Specifically, Ru and Ni of the present invention are applied to p-type GaN doped with Mg. FIG. 6 is a diagram showing a comparison between current-voltage characteristics of an electrode (α) containing the same and a conventional electrode (β) containing Ni and Au. This is because at least two electrodes made of each alloy are deposited on the surface of the Mg-doped GaN layer, annealed in an inert gas atmosphere at 400 ° C. or more for 5 minutes, and then the current-voltage characteristics between the same type of electrodes are obtained. Is measured.
In this figure, (a) contains 5 × 10 ¹⁷ / cm ³ of Mg,
(B) is 1 × 10 ¹⁸ / cm ³ , (c) is 1 × 10 ¹⁹ / cm ³ ,
(D) contains 2 × 10 ²⁰ / cm ³ .

As shown in this figure, when the Mg concentration is 5 × 10 ¹⁷
At / cm ³ , the carrier concentration of p-type GaN is still low, so that the Ni / Au electrode is close to a Schottky barrier. On the other hand, Ni / Ru has a lower contact resistance than Ni / Au and tends to be closer to ohmic. Next, when Mg becomes 1 × 10 ¹⁸ / cm ³ , it can be seen that a good ohmic has already been obtained with Ru / Ni. By using a positive electrode containing Ru and Ni in this way,
As compared with the conventional Ni / Au electrode, a good ohmic is obtained at a low Mg concentration.

The material of the positive electrode may be any metal containing Ru and Ni, and may contain other metals such as Pt, Au, Ti, and Pd. Ru and Ni may be formed independently, or may be formed in the form of an alloy from the beginning. When each is formed alone, the order of lamination is not particularly limited, but it is preferable that Ni is on the side in contact with the GaN layer. Further, the ratio of Ru to Ni is R
It is desirable that u be 0.1% by weight or more, more preferably 1% by weight or more, based on Ni. If the content is less than 0.1% by weight, it is difficult to obtain a preferable ohmic at a low Mg concentration. The upper limit is not particularly limited, but is adjusted to 95% by weight or less, more preferably 90% by weight or less based on Ni. If the content is more than 95% by weight, the adhesion to the p-type GaN layer is deteriorated, and the electrode tends to peel off. Such a composition is the same even when the positive electrode has a layered structure or an alloy.

[0014]

The present invention will be described in detail in the following examples. FIG.
FIG. 2 is a schematic cross-sectional view showing the structure of a laser device according to one embodiment of the present invention, and shows a structure when the device is cut in a direction perpendicular to a stripe-shaped positive electrode, that is, a direction perpendicular to a resonance direction of laser light. It shows. Hereinafter, the device of the present invention will be described with reference to this drawing. Note that the general formula In _x Al _Y Ga _{1 -XYN} shown in the present specification simply indicates the composition ratio of a nitride semiconductor. For example, even if different layers are represented by the same general formula, the The X and Y values of the layers do not match.

Example 1 A substrate 1 made of sapphire (C-plane) was set in a reaction vessel, and after sufficiently replacing the inside of the vessel with hydrogen, the temperature of the substrate was increased to 1050 ° C. while flowing hydrogen.
To clean the substrate. Another sapphire C face substrate 1, a sapphire having the principal R-plane, A plane, other, including other insulating substrate such as spinel _{(MgA1 2 O 4), SiC} (6H, 4H, and 3C ), S
A semiconductor substrate of i, ZnO, GaAs, GaN, or the like can be used.

(Buffer Layer 2) Subsequently, the temperature is set to 510 ° C.
The buffer layer 2 made of GaN is grown on the substrate 1 to a thickness of about 200 angstroms using hydrogen as a carrier gas and ammonia and TMG (trimethylgallium) as a source gas. The buffer layer 2 is made of AlN, Ga
N, AlGaN, etc., at a temperature of 900 ° C. or less,
m, preferably several tens to several hundreds of angstroms. This buffer layer is formed in order to alleviate the lattice constant mismatch between the substrate and the nitride semiconductor, but may be omitted depending on the growth method of the nitride semiconductor, the type of the substrate, and the like.

(N-side contact layer 3) Growth of buffer layer 2
After that, only TMG was stopped and the temperature was raised to 1050 ° C.
You. When the temperature reaches 1050 ° C, TMG is also used as the raw material gas.
Using silane gas as ammonia gas and impurity gas,
1 × 10 Si¹⁹/cm^ThreeConsisting of doped n-type GaN
The n-side contact layer 3 is grown to a thickness of 6 μm. n side
The contact layer 3 is an n-type In_XAl_YGa_1-XYN (0 ≦
X, 0 ≦ Y, X + Y ≦ 1), whose composition is particularly important
However, it is preferable that the n-type GaN has a Y value of 0.1
The following Al_XGa _1-XIf N, a good oh
Mick is easy to obtain.

(Crack prevention layer 4) Next, the temperature was set to 800
° C, and using TMG, TMI (trimethylindium), ammonia and silane gas as raw material gases,
A crack preventing layer 4 of In ¹⁹ Ga 0.9 N doped with 10 ¹⁹ / cm ³ is grown to a thickness of 500 Å. The crack prevention layer 4 is made of an n-type nitride semiconductor containing In, preferably InGaN, so that cracks can be prevented from entering the nitride semiconductor layer containing Al. This crack prevention layer is 10
It is preferable to grow the film with a thickness of 0 Å to 0.5 μm. If it is thinner than 100 Å, it is difficult to act as a crack prevention as described above,
If it is thicker than 0.5 μm, the crystals themselves tend to turn black. The crack preventing layer 4 may be omitted depending on conditions such as a growth method and a growth apparatus.

(N-side cladding layer 5)
C., and using TMA (trimethylaluminum), TMG, NH ₃ , and SiH ₄ as raw material gases,
¹⁹ / cm ³ doped with n-type Al0.20Ga0.80N made of a first layer of 20 angstroms and Si to 1 × 10 ¹⁹ / cm
^A second layer of ^3- doped n-type GaN is grown to 20 Å. Then, this pair is grown 125 times, and the total film thickness is 0.5 μm (5000 Å).
Is grown on the n-side cladding layer 5 composed of the multi-layer film. The n-side cladding layer 5 functions as a carrier confinement layer and a light confinement layer, and has a different composition from the first layer containing a nitride semiconductor containing Al, preferably AlGaN, or GaN or InGaN, and the first layer. It is desirable to grow a multilayer film layer having a laminated structure with a second layer made of a nitride semiconductor. As described above, when a superlattice structure in which nitride semiconductor layers having different compositions with a single film thickness of 100 Å or less, more preferably 70 Å or less, and most preferably 50 Å or less are laminated and grown, a single nitride When the thickness of the semiconductor layer becomes less than the critical limit thickness, the crystallinity becomes very good and continuous oscillation easily occurs at room temperature. The superlattice layer as the cladding layer is present in at least one of the n-type nitride semiconductor layer or the p-type nitride semiconductor layer outside the active layer, and is preferably present in both layers. It is desirable. It is desirable that the entire n-side cladding layer 5 be grown with a thickness of 100 Å or more and 2 μm or less, more preferably 500 Å or more and 1 μm or less.

(N-side light guide layer 6) Subsequently, at 1050 ° C.
Then, an n-side optical guide layer 6 made of n-type GaN doped with 1 × 10 ¹⁹ / cm ³ of Si is grown to a thickness of 0.2 μm.
The n-side light guide layer 6 functions as a light guide layer of an active layer, and is preferably used to grow GaN or InGaN. desirable. This layer may be non-doped (do not dope impurities).

(Active Layer 7) Next, TMG, T
The active layer 7 is grown using MI, ammonia, and silane gas. The active layer 7 is maintained at a temperature of 800.degree.
A well layer made of In0.2Ga0.8N doped with i at 8 × 10 ¹⁸ / cm ³ is grown to a thickness of 25 Å. Then, at the same temperature, only by changing the molar ratio of TMI, In0.01 Ga0.9 doped with 8 × 10 ¹⁸ / cm ^{3 of} Si.
A barrier layer of 5N is grown to a thickness of 50 Å. This operation is repeated twice to finally form a multiple quantum well structure in which well layers are stacked. The impurity doped into the active layer may be doped into both the well layer and the barrier layer as in this embodiment, or may be doped into either one. The threshold value tends to decrease when doped with an n-type impurity.

(P-side cap layer 8) Next, the temperature is set to 105
0 ℃, TMG, TMA, ammonia, Cp2Mg
(Cyclopentadienyl magnesium), the band gap energy is larger than that of the active layer, and Mg is 1 ×
A p-side cap layer 8 made of 10 ²⁰ / cm ³ doped p-type Al 0.1 Ga 0.9 N is grown to a thickness of 300 Å. Although the p-side cap layer 8 is p-type, it is thin, so that it may be i-type in which carriers are compensated by doping n-type impurities, or may be non-doped (in a state where impurities are not doped). Preferably, it is p-type.
The thickness of the p-side cap layer 8 is 0.1 μm or less, more preferably 500 Å or less, and most preferably 3 μm or less.
Adjust to less than 00 angstroms. This is because if the layer is grown with a thickness greater than 0.1 μm, cracks are likely to be formed in the p-side cap layer 8, and a nitride semiconductor layer having good crystallinity is difficult to grow. In addition, carriers cannot pass through the energy barrier due to the tunnel effect. When the composition ratio of Al is larger and the thickness of AlGaN is smaller, the LD element is more likely to oscillate. For example, Al _Y G having a Y value of 0.2 or more
If a ₁ -YN, it is desirable to adjust the thickness to 500 Å or less. The lower limit of the thickness of the p-side cap layer 8 is not particularly limited, but is preferably formed to a thickness of 10 Å or more.

(P-side light guide layer 9) Subsequently, at 1050 ° C.
And Mg-doped p-type G having a smaller band gap energy than the cap layer doped with Mg at 1 × 10 ²⁰ / cm ^3.
A p-type light guide layer 9 made of aN is grown to a thickness of 0.2 μm. This p-side light guide layer 9 is
Acts as a light guide layer for the active layer,
It is desirable to grow InGaN, and it is usually desirable to grow it to a thickness of 100 Å to 5 μm, more preferably 200 Å to 1 μm. This layer may also be non-doped.

(P-side cladding layer 10) Subsequently, at 1050 ° C.
And p-type Al0.20G doped with 1 × 10 ²⁰ / cm ^{3 of} Mg
a first layer of 0.80N is 20 Å;
A second layer of n-type GaN doped with 1 × 10 ²⁰ / cm ^{3 of} Mg is grown at 20 Å. Then, this pair is grown 125 times, and the total film thickness is 0.5 μm (500 μm).
A p-side cladding layer 10 composed of a multilayer film (0 angstrom) is grown. The p-side cladding layer 10 also functions as a carrier confinement layer and a light confinement layer, like the n-side cladding layer 5, and is formed of AlGaN, GaN, or IGaN.
It is desirable to grow a multilayer film layer having a laminated structure of a first layer made of nGaN and a second layer made of a nitride semiconductor having a composition different from that of the first layer. When the clad layer has a superlattice structure as described above, the thickness of a single nitride semiconductor layer becomes equal to or less than the critical thickness, the crystallinity becomes very good, and continuous oscillation easily occurs at room temperature. It is also very effective as a light confinement layer for confining light emission of the active layer. The total thickness of the p-side cladding layer 10 is 100 Å or more and 2 μm or less, and more preferably 50 Å or less.
It is desirable to grow the layer at a thickness of 0 Å to 1 μm.

In the case of a semiconductor device having a double hetero structure having an active layer having a quantum well layer as in this embodiment, a film thickness in contact with the active layer 7 and having a band gap energy larger than that of the active layer 7. A cap layer made of a nitride semiconductor of 0.1 μm or less, preferably a p-side cap layer 8 made of a nitride semiconductor containing Al is provided, and a p-side cap is provided at a position farther from the active layer than the p-side cap layer 8. A p-side light guide layer 9 having a smaller band gap energy than the layer 8 is provided, and a nitride semiconductor having a band gap larger than the p-side light guide layer 9 is provided at a position farther from the active layer than the p-side light guide layer 9. It is very preferable to provide the p-side cladding layer 10 having a superlattice structure including a nitride semiconductor preferably containing Al. Moreover, the p-side cap layer 8
Is set to be as thin as 0.1 μm or less, so that it does not act as a carrier barrier, and holes injected from the p-layer can pass through the p-side cap layer 8 by a tunnel effect. Recombine efficiently in the active layer,
The output of the LD is improved. That is, the injected carriers have a large band gap energy of the p-side cap layer 8, so that the carriers do not overflow the active layer even if the temperature of the semiconductor element is increased or the injected current density is increased. Since the carrier is blocked by the side cap layer 8, carriers are accumulated in the active layer, and light can be efficiently emitted.

(P-side contact layer 11) Finally, Mg is deposited on the p-side cladding layer 10 at 1050 ° C. at 1 × 10 ²⁰ / Mg.
p-side contact layer 1 made of p-type GaN doped with cm ³
1 is grown to a thickness of 150 angstroms. The p-side contact layer 11 is formed of a p-type In _x Al _Y Ga _{1 -XYN} (0
≦ X, 0 ≦ Y, X + Y ≦ 1), preferably Mg-doped GaN, or Mg-doped Al _Y Ga _1-Y N having a Y value of 0.1 or less, The most favorable ohmic contact with the positive electrode 20 is obtained. The thickness of the p-side contact layer 20 is 500 Å or less,
More preferably, it is adjusted to 300 angstrom or less, most preferably to 200 angstrom or less. The reason is that by adjusting the thickness of the p-type nitride semiconductor layer having a high resistivity to 500 Å or less, the resistivity further decreases, so that the threshold current and voltage decrease. Further, the amount of hydrogen removed from the p-type layer during annealing tends to increase and the resistivity tends to decrease. Further, the effect of reducing the thickness of the p-side contact layer 11 is as follows.
There are the following: For example, a p-side contact layer made of p-type GaN having a thickness greater than 500 angstroms is formed in contact with a p-side clad layer made of p-type AlGaN, and if the impurity concentration of the clad layer and the contact layer is the same, When the carrier concentration is the same, when the thickness of the p-side contact layer is smaller than 500 angstroms, the carrier on the cladding layer side easily moves to the contact layer side, and the carrier concentration on the p-side contact layer tends to increase. It is in. Therefore, p which forms the positive electrode 20
The carrier concentration of the side contact layer 11 is substantially increased, and a good ohmic is obtained.

After the reaction is completed, the temperature is lowered to room temperature, and the wafer is placed in a nitrogen atmosphere in a reaction vessel.
Anneal at ℃ to further reduce the resistance of the p-type layer.

After the annealing, the wafer is taken out of the reaction vessel and etched by an RIE apparatus. As shown in FIG. 2, the uppermost p-side contact layer 11 and the p-side cladding layer 10 are etched to form a 4 μm stripe. A ridge stripe having a width is formed. When forming the ridge stripe, the ridge stripe is designed in advance so that the center of the stripe width approaches the negative electrode 22 to be formed later. In the case of forming a ridge stripe, in particular, the Al layer above the active layer
By forming a layer more than the p-type nitride semiconductor layer including ridges into a ridge shape, light emission of the active layer is concentrated on the lower portion of the ridge, the transverse mode is easily united, and the threshold value is easily lowered. In addition, when an insulating substrate is used as in the present embodiment, shifting the center of the stripe of the ridge portion to the center of the stripe of the active layer and approaching to the negative electrode 22 side reduces the threshold value. preferable.

Next, a mask is formed on the surface of the ridge stripe and the exposed surface of the p-side cladding layer 10,
Similarly, etching is performed by RIE to expose the surface of the n-side contact layer 3 where the negative electrode 22 is to be formed, as shown in FIG. After the surface is exposed, as shown in FIG.
A positive electrode 20 made of an alloy containing 50% of Ru and 50% of Ni is formed to a thickness of 500 Å on the entire upper surface of the ridge stripe of the side contact layer 11.

Next, on the exposed surface of the n-side contact layer 3, a negative electrode 22 made of Ti and Al is formed in a thickness of 0.5 μm in parallel with the ridge stripe. Note that n
As the material of the side contact layer 3 and the negative electrode 22 that can obtain a preferable ohmic, Al, Ti, W, Cu, Zn,
Metals or alloys such as Sn and In can be used.

Next, an insulating film 12 made of SiO ₂ is formed to a thickness of 0.5 μm on the entire surface of the nitride semiconductor layer except for the positions where the positive electrode 20 and the negative electrode 22 are formed. After the insulating film 12 is formed, the extraction pad electrode 21 including Ru and Au electrically connected to the positive electrode 20 is formed on the positive electrode 20.
Is formed with a thickness of 2 μm over the surface area of the positive electrode via the insulating film 12. The pad electrode 21 does not need to have an ohmic contact with the p-side contact layer 11 and only needs to be electrically connected to the positive electrode 20. Preferably, in the device of the present invention, N
A pad electrode containing at least two or more elements selected from the group consisting of i, Ru, Au, Ti, and Pt and having a larger surface area than the positive electrode is formed to have a larger thickness than the positive electrode. desirable. Since the pad electrode is thicker than the positive electrode to prevent peeling of the positive electrode and has a larger surface area than the positive electrode, in the case of a laser device such as the present embodiment, In addition to facilitating wire bonding from the pad electrode to the positive electrode side, and when connecting the positive electrode side to a radiator such as a heat sink or a submount, the bonding area is increased to improve heat dissipation.

As described above, the negative electrode 22 and the positive electrode 2
The wafer on which 0 is formed is transferred to a polishing apparatus, and the substrate 1 on which the nitride semiconductor is not formed is wrapped using a diamond abrasive to make the thickness of the substrate 100 μm. After lapping, the substrate surface is mirror-finished by polishing with a finer abrasive at 1 μm. By thus reducing the thickness of the substrate to 100 μm or less, the heat dissipation of the laser element is improved.

After the substrate is polished, the polished surface side is scribed,
Cleavage is performed in a bar shape in the direction perpendicular to the ridge stripe, and a resonator having a cavity length of 500 μm is formed on the cleavage plane. Further, a dielectric multilayer film made of SiO ₂ and TiO ₂ is formed on the resonator surface, and finally, the bar is cut in a direction parallel to the ridge stripe to form a laser chip.

Finally, this laser chip is placed on the heat sink face up (in a state where the substrate and the heat sink face each other), and each electrode is bonded with a wire 28 made of a gold wire. Note that the position at the time of wire bonding is a position apart from the position of the ridge stripe as shown in FIG. By avoiding the area right above the ridge stripe, no impact is applied to the ridge portion, so that the crystal in the ridge portion is not broken. Then, when the laser oscillation of this laser chip was attempted, the oscillation wavelength was 40 at room temperature.
5 nm continuous oscillation was confirmed, and Ni and Au were applied to the positive electrode 20.
Compared with the laser device having the electrodes formed of the electrodes, the threshold current density was reduced by 5% and the threshold voltage was reduced by 2%, and the life was 1.5 times or more.

[Embodiment 2] In Embodiment 1, the positive electrode 2
When 0 was formed, a laser element was fabricated in the same manner as in Example 1 except that Ni was first evaporated to a thickness of 100 Å, and Ru was deposited thereon to a thickness of 400 Å. A laser device having the following characteristics was obtained.

[Embodiment 3] In Embodiment 1, the positive electrode 2
When forming 0, Ni is first deposited in a thickness of 100 angstroms, Ru is deposited thereon in a thickness of 100 angstroms, and Au is deposited thereon in a thickness of 200 angstroms. As a result, a laser element having substantially the same characteristics as in Example 1 was obtained.

Example 4 A laser device was obtained in the same manner as in Example 1 except that the Mg concentration of the p-side contact layer was changed to 5 × 10 ¹⁹ / cm ^3, and the characteristics were almost the same as those in Example 1. Was obtained.

Fifth Embodiment In the first embodiment, the Mg concentration of the p-side cladding layer 10 is set to 1 × 10 ¹⁹ / cm ³ and the Mg concentration of the p-side contact layer is set to 5 × 10 ¹⁸ / cm ^3. When a laser element was obtained in the same manner, a 7% increase in threshold current density and a 3% increase in threshold voltage were observed as compared with Example 1. However, an alloy composed of Ni and Au was used for the positive electrode. The threshold current density and the threshold voltage were still lower by 10% and 4%, respectively, as compared with the laser device similar to that of Example 5 formed.

[0039]

As described above, in the device of the present invention, a good ohmic can be obtained even with a p-type nitride semiconductor doped with a low concentration of p-type impurities. It is very effective for light emitting devices that need to be lowered. In addition, since a stable ohmic is obtained, the probability of occurrence of a defect due to the positive electrode in the manufacturing process is reduced, and an element having excellent reliability can be provided. In this specification, a laser device has been described. However, the present invention is not limited to a laser device, but may be any device such as an LED or a light receiving device as long as it is a nitride semiconductor device having a positive electrode formed on a p-type nitride semiconductor. But it is applicable.

[Brief description of the drawings]

FIG. 1 is a diagram showing current-voltage characteristics of positive electrodes formed on p-type GaN layers having different p-type impurity concentrations in comparison with (a) to (d).

FIG. 2 is a schematic sectional view showing the structure of a laser device according to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... Buffer layer 3 ... n-side contact layer 4 ... Crack prevention layer 5 ... n-side cladding layer 6 ... n-side light guide layer 7 ··· Active layer 8 ··· Cap layer 9 ··· p-side light guide layer 10 ··· p-side cladding layer 11 ··· p-side contact layer 12 ··· insulating film 20 · ... Positive electrode 21 ... Pad electrode 22 ... Negative electrode 23 ... Wire

Claims (3)

[Claims] 1. A nitride semiconductor device, wherein a positive electrode containing at least ruthenium (Ru) and nickel (Ni) is formed on a surface of a p-type nitride semiconductor layer doped with a p-type impurity. . 2. The p-type nitride semiconductor layer, wherein Mg is 5 ×
2. The nitride semiconductor device according to claim 1, wherein the nitride semiconductor device is doped with 10 ¹⁷ / cm ³ or more and 2 × 10 ²⁰ / cm ³ or less. 3. The p-type nitride semiconductor layer has a thickness of 400.
2. The method according to claim 1, wherein the distance is equal to or less than Å.
Or the nitride semiconductor device according to 2.