JPH06275868A - Formation of electrode of gallium nitride-based compound semiconductor - Google Patents

Abstract

PURPOSE:To provide the formation method, of an electrode, wherein the n-type layer and the p-type layer of a p-n junction-type gallium nitride-based compound semiconductor as well as an ohmic contact are obtained in order to enhance the light-emitting output and the light-emitting efficiency of a light-emitting element which utilizes the gallium nitride-based compound semiconductor. CONSTITUTION:An alloy which contains chromium and/or nickel or the metals are applied to an n-type gallium nitride-based compound semiconductor at an electron carrier concentration of 1X10<17>/cm<3> or higher or to a p-type gallium nitride-based compound semiconductor at an electron carrier concentration of 1X10<15>/cm<3> or higher, and an annealing operation is then performed.

Description

Detailed Description of the Invention

[0001]

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-XY N (0 ≦ X <1, 0 ≦ Y <1), and particularly to an n-type gallium nitride-based compound semiconductor and a p-type gallium nitride-based compound semiconductor The present invention relates to a method for forming an electrode that can achieve ohmic contact with

[0002]

2. Description of the Related Art GaN, GaAlN, InGaN, In
Gallium nitride-based compound semiconductors such as AlGaN are {In _x
Al _Y Ga _1-XY N (0 ≦ X <1, 0 ≦ Y <1)} has a direct transition, and the band gap changes from 1.95 eV to 6 eV, so that a light emitting diode, a laser diode, etc.
It is regarded as a promising material for light emitting devices. It is known that this material exhibits an n-type characteristic in a non-doped state or by being doped with an n-type dopant such as Si or Ge. On the other hand, regarding p-type characteristics, recently, gallium nitride-based compound semiconductors doped with p-type dopants
With the development of p-type gallium nitride-based compound semiconductors, it has become possible to realize p-type gallium nitride compound semiconductors. (For example, Japanese Patent Laid-Open No.
-257679, JP-A-3-218325)

As described above, if a p-type gallium nitride compound semiconductor can be realized, 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 device, an n-type gallium nitride-based compound semiconductor, and p
It is essential that the electrodes formed on the gallium nitride-based compound semiconductor have ohmic contact with those gallium nitride-based compound semiconductors. However, the physical properties of gallium nitride-based compound semiconductors have not yet been clarified, and the reality is that no electrode material capable of obtaining ohmic contact has yet been known.

[0004]

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

[0005]

The electrode forming method of the present invention comprises an n-type gallium nitride compound semiconductor having an electron carrier concentration of 1 × 10 ¹⁷ / cm ³ or more, or a hole carrier concentration of 1 ×
It is characterized in that an alloy containing chromium and / or nickel or the metal is adhered to a p-type gallium nitride 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 must 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 compound semiconductor must be an alloy containing chromium and / or nickel, or a metal thereof. Specific metals are Cr and Ni alone, and alloys are Au, Pt, and M.
An alloy of at least one metal selected from o, Ti, In, and Ga and Cr, an alloy of Ni, or a Cr—Ni alloy can be used, and especially Cr, Ni.
Alone 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 higher the Cr and Ni contents, the more preferable.

To deposit the above electrode material on the gallium nitride-based compound semiconductor, a vapor deposition method can be preferably used, and a metal or a metal simple substance which has been alloyed in advance can be deposited as a vapor deposition material.

Annealing is performed to make the electrode material and the gallium nitride-based compound semiconductor conform to each other, and preferably 40
By carrying out at a temperature of 0 ° C. or higher, the above electrode material can be brought into ohmic contact. In addition, annealing is preferably performed in a nitrogen atmosphere, whereby nitrogen in the gallium nitride-based compound semiconductor can be prevented from decomposing and flowing out, and crystallinity can be maintained. The upper limit of the annealing temperature is not particularly limited, but it is usually preferably 1100 ° C. or lower. This is because when the temperature exceeds 1100 ° C, the gallium nitride-based compound semiconductor tends to decompose as described above. Further, the p-type gallium nitride compound semiconductor is
By depositing the electrode material with a width of 20 μm or less and then performing annealing at 400 ° C. or higher, the resistivity of the p-type gallium nitride compound semiconductor is lowered, and a more preferable p-type can be obtained.

[0010]

Operation: FIG. 1 shows S having different electron carrier concentrations.
An electrode made of a Cr—Ni alloy was attached to the i-doped n-type GaN layer, annealed at 500 ° C. for 15 minutes, and then the current-voltage characteristics between the respective Cr—Ni electrodes were measured.
It is a figure which compares and shows the result of having investigated the ohmic contact of an n-type GaN layer and an electrode. A is 2 × 10 ¹⁹ / cm ³ , B is 1
× 10 ¹⁸ / cm ³ , C is 1 × 10 ¹⁷ / cm ³ , D is 6 × 10 ^16.
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 , it can be seen that the voltage and the current are not completely in a linear relationship and no ohmic contact is made.

Further, in FIG. 2, electrodes made of a Cr-Ni alloy are adhered to Mg-doped p-type GaN layers having different hole carrier concentrations, each is annealed at 500 ° C. for 15 minutes, and then each Cr-Ni is deposited. It is a figure which compares and shows the result of having measured the current voltage characteristic between electrodes, and checking 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 in the vicinity of the hole carrier concentration of 1 × 10 ¹⁵ / cm ³ , and it is difficult to obtain ohmic contact below the limit value.

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

[0013]

EXAMPLES Example 1 Using a MOCVD method, a GaN buffer layer having a thickness of about 200 Å is formed on a sapphire substrate, and a non-doped GaN layer having a thickness of 2 μm is formed thereon.
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 at 700 ° C. for 10 minutes in a nitrogen atmosphere to further reduce the resistance of the Mg-doped Ga0.9Al0.1N layer to p-type. As a result of hole measurement, the hole carrier concentration of this Mg-doped p-type Ga0.9Al0.1N layer is 1 × 10.
It was ¹⁷ / cm ³ .

Next, N is formed on the surface of the p-type Ga0.9Al0.1N layer.
After depositing the i-Au alloy, the substrate is also placed in an annealing apparatus and annealed at 500 ° C. for 10 minutes in a nitrogen atmosphere. After the annealing was completed, the current-voltage characteristics between the electrodes were measured, and when the ohmic contact between the p-type Ga0.9Al0.1N layer and the electrodes was examined, the same straight line as in Fig. 2 and E was obtained, and ohmic contact was obtained. Was confirmed.

[Embodiment 2] In Embodiment 1, p-type Ga is used.
An electrode was formed in the same manner except that the electrode material 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
An n-type In0.1Ga0.9N layer doped with Si is grown to a thickness of 0.2 μm on the layer, and then an alloy of Ni is vapor-deposited thereon to attach an electrode. This Si-doped In0.1Ga0.9
The electron carrier concentration of the N layer was 2 × 10 ¹⁹ / cm ³ .
After that, after annealing as in Example 1, the current-voltage characteristics between the electrodes were measured, and Si-doped n-type In0.1Ga0.9 was measured.
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.

[Embodiment 4] The same operation as in Embodiment 3 is performed except that the Si doping amount in the Si-doped n-type In0.1Ga0.9N layer is changed so that the electron carrier concentration is 1 × 10 ¹⁸ / cm ^3. When a Ni electrode was formed and the current-voltage characteristics were measured, the same straight line as in FIG. 1B was obtained, and ohmic contact was confirmed.

[0018]

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

[Brief description of drawings]

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

FIG. 2 Mg-doped p-type G having different hole carrier concentrations
The figure which compares and shows the relationship of the current voltage characteristic of an aN layer and an electrode.

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

Claims (2)

[Claims] 1. An n-type gallium nitride-based compound semiconductor having an electron carrier concentration of 1 × 10 ¹⁷ / cm ³ or more or a p-type gallium nitride-based compound semiconductor having a hole carrier concentration of 1 × 10 ¹⁵ / cm ³ or more, and chromium and And / or an alloy containing nickel, or a method of forming an electrode of a gallium nitride-based compound semiconductor, which comprises depositing the metal and then annealing. 2. 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.