JP2803741B2 - Gallium nitride based compound semiconductor electrode forming method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the general formula In _x Al _Y Ga
_{The present} invention relates to a method for forming an electrode of a gallium nitride-based compound semiconductor represented by _1-XYN (0 ≦ X <1, 0 ≦ Y <1), particularly an n-type gallium nitride-based compound semiconductor and a p-type gallium nitride-based compound semiconductor And a method of forming an electrode capable of obtaining ohmic contact with the electrode.

[0002]

2. Description of the Related Art GaN, GaAlN, InGaN, In
Gallium nitride based compound semiconductor such as AlGaN is ｛In _X
Al _Y Ga ₁ -XYN (0 ≦ X <1, 0 ≦ Y <1)} has a direct transition and the band gap changes from 1.95 eV to 6 eV.
Promising as a material for light-emitting elements. It is known that this material exhibits n-type characteristics in a non-doped state or by doping with an n-type dopant such as Si or Ge. On the other hand, with regard to p-type characteristics, a gallium nitride-based compound semiconductor doped with a p-type
A technology for forming a mold has been developed, and a p-type gallium nitride-based compound semiconductor has been realized. (See, for example,
-257679, JP-A-3-218325)

As described above, when a p-type gallium nitride-based compound semiconductor becomes feasible, a pn junction type light emitting device having a high light emission output is required. In the case of a pn junction type light emitting element, an n-type gallium nitride based compound semiconductor and p-type
It is essential that the electrodes formed on the gallium nitride-based compound semiconductors are in ohmic contact with those gallium nitride-based compound semiconductors. However, the physical properties of gallium nitride-based compound semiconductors have not yet been elucidated yet, and in reality, there is no known electrode material capable of obtaining ohmic contact.

[0004]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made in view of such circumstances, and an object thereof is to provide a light emitting device using a pn junction type gallium nitride-based compound semiconductor. In order to improve the luminous output and luminous efficiency of the GaN layer, it is an object of the present invention to provide a method for forming an electrode capable of obtaining ohmic contact with an n-type layer and a p-type layer of a gallium nitride compound semiconductor.

[0005]

According to the electrode forming method of the present invention, an n-type gallium nitride-based compound semiconductor having an electron carrier concentration of 1 × 10 ¹⁷ / cm ³ or more, or a hole carrier concentration of 1 × 10 ¹⁷ / cm ^{3 is used.}
An alloy containing chromium and / or nickel or the metal is deposited on a p-type gallium nitride-based compound semiconductor of 10 ¹⁵ / cm ³ or more, and then annealed.

In the electrode forming method of the present invention, what is particularly important is that the electron carrier concentration of the n-type gallium nitride compound semiconductor forming the electrode needs to be 1 × 10 ¹⁷ / cm ³ or more. If the concentration is less than 1 × 10 ¹⁷ / cm ³ , good ohmic contact with the n-type layer cannot be obtained. Similarly, the hole carrier concentration of the p-type gallium nitride-based compound semiconductor forming the electrode needs to be 1 × 10 ¹⁵ / cm ³ or more. If it is less than 1 × 10 ¹⁵ / cm ³ , good ohmic contact with the p-type layer cannot be obtained.

Next, an n-type gallium nitride compound semiconductor,
The electrode material attached to the p-type gallium nitride-based compound semiconductor needs to be an alloy containing chromium and / or nickel or its metal. Specific metals are Cr and Ni alone, and alloys are Au, Pt, M
An alloy of at least one metal selected from o, Ti, In, and Ga with Cr, an alloy of Ni, or a Cr—Ni alloy can be used.
Single or Cr-Ni alloy, Cr-Au alloy, Ni-
Au alloys are preferred. The Cr and Ni contents of the alloy are not particularly limited, but the more Cr and Ni, the better.

In order to attach the above-mentioned electrode material to the gallium nitride-based compound semiconductor, an evaporation method can be preferably used, and a metal or a simple metal which has been alloyed in advance can be attached as an evaporation material.

Annealing is performed to make the electrode material compatible with the gallium nitride-based compound semiconductor.
By performing the treatment at a temperature of 0 ° C. or higher, the electrode material can be brought into ohmic contact. Further, by performing annealing in a nitrogen atmosphere, nitrogen in the gallium nitride-based compound semiconductor can be prevented from decomposing and leaving, and crystallinity can be maintained. Although the upper limit of the annealing temperature is not particularly limited, it is usually preferable to perform the annealing at 1100 ° C. or lower. If the temperature exceeds 1100 ° C., the gallium nitride-based compound semiconductor tends to be easily decomposed as described above. Further, the p-type gallium nitride based compound semiconductor,
After depositing the electrode material with a width of 20 μm or less, by performing annealing at 400 ° C. or more, the resistivity of the p-type gallium nitride-based compound semiconductor decreases, and a more preferable p-type can be obtained.

[0010]

FIG. 1 is a schematic diagram showing S carriers having different electron carrier concentrations.
After attaching an electrode made of a Cr-Ni alloy to the i-doped n-type GaN layer and annealing at 500 ° C. for 15 minutes, current-voltage characteristics between the respective Cr-Ni electrodes were measured.
FIG. 6 is a diagram showing a comparison of the results of an examination of ohmic contact between an n-type GaN layer and an electrode. A is 2 × 10 ¹⁹ / cm ³ , B is 1
× 10 ¹⁸ / cm ³ , C 1 × 10 ¹⁷ / cm ³ , D 6 × 10 ¹⁶
4 is an n-type GaN layer having an electron carrier concentration of / cm ³ . As can be seen by comparing A to D, ohmic contact is easily obtained in the n-type GaN layer having a high electron carrier concentration, and ohmic contact is still obtained at 1 × 10 ¹⁷ / cm ³ , but 6 × At 10 ¹⁶ / cm ³ , the voltage and the current were not completely in a linear relationship, indicating that there was no ohmic contact.

FIG. 2 shows that an electrode made of a Cr—Ni alloy is adhered to Mg-doped p-type GaN layers having different hole carrier concentrations, and annealed at 500 ° C. for 15 minutes. It is a figure which shows the current-voltage characteristic between electrodes, and compares and shows the result of having investigated the ohmic contact of a p-type GaN layer and an electrode. E is 1 × 10
¹⁷ / cm ³ , F is 1 × 10 ¹⁶ / cm ³ , G is 1 × 10 ¹⁵ / c
m ³ and H are p-type GaN layers having a hole carrier concentration of 5 × 10 ¹⁴ / cm ³ . This figure also shows that there is a limit value of ohmic contact near the hole carrier concentration of 1 × 10 ¹⁵ / cm ³ , and it is difficult to obtain ohmic contact below the limit value.

FIG. 3 shows a hole carrier concentration of 4 × 10
^{When a} Ni-Cr alloy is deposited on a ¹⁶ / cm ³ Mg-doped p-type GaN layer and then annealed at a different temperature for 15 minutes, the relationship between the current-voltage characteristics of the p-type GaN layer and the electrode depending on the annealing temperature FIG. I is before annealing, J is 200 ° C, K is 300
C and L indicate an annealing temperature of 400C. I
L show ohmic contact between the annealing temperature and the p-type GaN layer.
The contact resistance between the aN layer and the electrode decreases and the slope increases,
Also, it can be seen that the current value increases in proportion to the voltage and ohmic contact is obtained. Therefore, the preferred annealing temperature is 400 ° C. or higher.

[0013]

[Example 1] Using a MOCVD method, a buffer layer made of GaN was formed on a sapphire substrate by about 200 angstroms, and a non-doped GaN layer was formed thereon by 2 μm.
Then, a Ga0.9Al0.1N layer doped with Mg is grown to a thickness of 0.2 μm on the GaN layer. Mg
After the growth of the doped Ga0.9Al0.1N layer, the substrate is placed in an annealing apparatus and annealed in a nitrogen atmosphere at 700 ° C. for 10 minutes to further reduce the resistance of the Mg-doped Ga0.9Al0.1N layer to a p-type. As a result of the hole measurement, the hole carrier concentration of the Mg-doped p-type Ga0.9Al0.1N layer was 1 × 10
¹⁷ / cm ³ .

Next, N is added to the surface of the p-type Ga0.9Al0.1N layer.
After depositing the i-Au alloy, the substrate is similarly placed in an annealing apparatus and annealed at 500 ° C. for 10 minutes in a nitrogen atmosphere. After the end of the annealing, the current-voltage characteristics between the electrodes were measured, and the ohmic contact between the p-type Ga0.9Al0.1N layer and the electrode was examined. The same straight line as in FIGS. 2 and E was obtained, and the ohmic contact was obtained. It was confirmed that.

[Embodiment 2] In Embodiment 1, p-type Ga
An electrode was formed in the same manner except that the electrode material to be deposited on the 0.9Al0.1N layer was a Cr-Au alloy, and the current-voltage characteristics were measured. Similarly, the same straight line as in FIGS. 2 and E was obtained.
Ohmic contact was confirmed.

Embodiment 3 Non-doped GaN of Embodiment 1
After growing a Si-doped n-type In0.1Ga0.9N layer to a thickness of 0.2 μm on the layer, an electrode of Ni is deposited thereon by vapor deposition of a Ni alloy. The Si-doped In0.1Ga0.9
The electron carrier concentration of the N layer was 2 × 10 ¹⁹ / cm ³ .
Thereafter, after annealing as in Example 1, the current-voltage characteristics between the electrodes were measured, and the Si-doped n-type In0.1Ga0.9
When the ohmic contact between the N layer and the electrode was examined, FIG.
The same straight line as in A was obtained, and ohmic contact was confirmed.

Example 4 The procedure of Example 3 was repeated, except that the amount of Si doped in the Si-doped n-type In0.1Ga0.9N layer was changed and the electron carrier concentration was 1 × 10 ¹⁸ / cm ^3. When a Ni electrode was formed and current-voltage characteristics were measured, the same straight line as in FIGS. 1 and B was obtained, and ohmic contact was confirmed.

[0018]

As described above, according to the method of the present invention, an ohmic contact between the n-type and p-type gallium nitride-based compound semiconductors and the electrodes can be obtained. When a light-emitting element such as an n-junction light-emitting diode or a laser diode is manufactured, the forward voltage of the light-emitting element can be reduced and the luminous efficiency can be improved, which is of great industrial value.

[Brief description of the drawings]

FIG. 1 is a diagram showing a comparison of current-voltage characteristics between an n-type GaN layer having different electron carrier concentrations and an electrode.

FIG. 2 shows Mg-doped p-type G having different hole carrier concentrations.
FIG. 7 is a diagram showing a comparison of current-voltage characteristics between an aN layer and an electrode.

FIG. 3 is a graph showing a comparison of a current-voltage characteristic between a p-type GaN layer and an electrode depending on an annealing temperature.

Continuation of the front page (56) References JP-A-49-29771 (JP, A) JP-A-4-213878 (JP, A) JP-A-4-68579 (JP, A) (58) Fields investigated (Int .Cl. ⁶ , DB name) H01L 33/00 H01S 3/18 JICST file (JOIS)

Claims (3)

(57) [Claims] Claims 1. A method comprising: growing on a non-doped GaN layer;
After attaching an alloy containing chromium and / or nickel or its metal to an n-type gallium nitride-based compound semiconductor having an electron carrier concentration of 1 × 10 ¹⁷ / cm ³ or more, annealing is performed to bring the electrode into ohmic contact. A method for forming an electrode of a gallium nitride-based compound semiconductor. 2. An alloy containing chromium and / or nickel or its metal is attached to p-type GaN doped with Mg having a hole carrier concentration of 1 × 10 ¹⁵ / cm ³ or more, and then annealed. Forming a gallium nitride-based compound semiconductor electrode by reducing the resistivity of the GaN type GaN and making an ohmic contact with the electrode. 3. The method for forming an electrode of a gallium nitride-based compound semiconductor according to claim 1, wherein the annealing temperature is 400 ° C. or higher.