JPH06232450A - Gallium nitride compound semiconductor and forming method of electrode thereof - Google Patents

Abstract

PURPOSE:To improve an emission output of a light-emitting element using a gallium nitride compound semiconductor, to lower also a forward voltage and a forward current and thereby to make the light-emitting element be of practical use. CONSTITUTION:After an electrode having a width of 20mum or below is deposited on a gallium nitride compound semiconductor doped with a p-type dopant, the gallium nitride compound semiconductor is annealed at a temperature of 400 deg.C or above, so that the electrode be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention mainly relates to a detailed structure of a gallium nitride-based compound semiconductor used for a light emitting device such as a blue light emitting diode and a blue light emitting laser diode, and more particularly to a nitride doped with a p-type dopant. The present invention relates to a gallium compound semiconductor and an electrode forming method thereof.

[0002]

2. Description of the Related Art Gallium nitride (GaN), indium gallium nitride (InGaN), gallium aluminum nitride (GaAlN), and nitride are practical semiconductor light emitting device materials used for blue light emitting diodes (LEDs), blue laser diodes, and the like. Attention has been focused on gallium nitride-based compound semiconductors such as indium aluminum gallium (InAlGaN).

The structure of an LED element using, for example, GaN will be described with reference to FIGS. 1 and 2. FIG. 1 is a sectional view showing the structure of a conventional LED device, and FIG. 2 is a plan view of this device seen from the electrode side. In this device, a buffer layer 2 made of AlN, an n-type GaN layer 3, and a high-resistance i-type GaN layer 4 doped with a p-type dopant are sequentially laminated on a substrate 1 basically made of sapphire. The n-type GaN layer 3 has an electrode (hereinafter, referred to as an n-type electrode) 5 and the i-type GaN layer 4 has an electrode (hereinafter, referred to as a p-type electrode) 6. Then, by supplying electricity between these electrodes, the light emitted from the i-type GaN layer 4 is
It can be observed from the sapphire substrate 1 side which is a translucent substrate. In particular, as shown in FIG. 2, by forming the p-type electrode 6 on almost the entire surface of the i-type GaN layer 4, i-type Ga is formed.
The contact resistance between the N layer 4 and the p-type electrode 6 is lowered, and the forward voltage is lowered.

[0004]

However, in the conventional light emitting element, the p-type electrode 6 is shown in FIG. 2 because the i-type GaN layer 4 has a very high resistivity of 10 ⁶ Ω · cm or more. Even if formed on almost the entire surface, the p-type electrode 6 does not make ohmic contact with the i-type GaN layer. For example, at a forward current of 10 mA, the forward voltage is still high at 20 to 30 V, and the light emission output is high. Was only a few μW, which was not a satisfactory characteristic for an LED.

The present invention has been made in view of such circumstances, and an object of the present invention is to improve the light emission output of a light emitting device using a gallium nitride compound semiconductor, and to improve the forward voltage and the forward current. Is lowered to obtain a practical light emitting element.

[0006]

[Means for Solving the Problems] In order to achieve the above-mentioned object, we have conducted a number of experiments and found that an electrode formed on a gallium nitride-based compound semiconductor, especially a high-resistance i-type nitride doped with a p-type dopant. The inventors have found that the above problems can be solved by making the gallium compound semiconductor to have a low resistance p-type and improving the method for forming the p-type electrode of the gallium nitride compound semiconductor, and have completed the present invention. That is, the gallium nitride-based compound semiconductor of the present invention has p
A p-type electrode having a width of 20 μm or less, which is ohmic-contacted by annealing, is formed on a gallium nitride-based compound semiconductor doped with a type dopant. Moreover, the p-type electrode is formed on the gallium nitride-based compound semiconductor doped with a p-type dopant.
It can be formed by depositing an electrode having a width of 0 μm or less and then annealing the gallium nitride-based compound semiconductor at 400 ° C. or higher.

The p-type electrode needs to be an electrode having a width of 20 μm or less, and its shape and length are irrelevant.
In order to uniformly spread the current, it is preferable to form the p-type layer over the entire surface as long as possible. For example, if the shape is a circle, the diameter is 20 μm or less, and if it is an ellipse, the minor axis is 20 μm.
It is necessary that the thickness be less than or equal to μm, and innumerable circular and elliptical electrodes can be formed on the entire surface of the p-type layer. Further, as shown in FIG. 6, a plurality of p-type electrodes 6 having a width of 20 μm or less are formed, and in order to electrically connect the p-type electrodes 6 from above, a conductive material such as Au, In, Al, or solder is used. You may coat with.

As a method of attaching the electrode to the gallium nitride compound semiconductor doped with p-type impurities, for example, a method such as vapor deposition, sputtering or plating can be used, and an appropriate mask such as photoresist is used for the gallium nitride compound semiconductor. Formed on top and through the mask, width 2
It can be 0 μm or less. As the electrode material, for example, Au, Pt, Ni, In or alloys thereof can be used.

[0009]

The operation of the p-type electrode according to the present invention will be described below with reference to FIGS. 3 and 4. FIG. 3 shows p according to the present invention.
FIG. 4 is a partial cross-sectional view showing the structure of the i-type GaN layer 4 having the type electrode 6 formed therein, and FIG. 4 is a partial cross-sectional view showing the structure of the i-type GaN layer 4 having the p-type electrode 6 formed by the conventional method.

As described above, the i-type GaN layer 4 doped with the p-type dopant is a layer having a resistivity of 10 ⁶ Ω · cm or more and is almost an insulator. This high resistance i-type GaN
In order to make the layer a p-type with low resistance, we first applied Japanese Patent Application No. 3-3.
In No. 21353, a technique of making this i-type GaN layer into a p-type having low resistance by annealing at 400 ° C. or higher was proposed. Moreover, the action of i-type GaN doped with a p-type dopant to become a p-type with low resistance by annealing is as follows. When a gallium nitride-based compound semiconductor is grown, a gas containing hydrogen atoms such as NH ₃ is used as a source gas, and the hydrogen atoms (H) are mixed with p-type dopant (M) and M in the gallium nitride-based compound semiconductor.
The i-type GaN layer has a high resistance by binding in the -H state and making the p-type dopant inactive. Therefore, by heat generated by annealing, H is dissociated from the p-type dopant bound by MH and removed from the gallium nitride-based compound semiconductor layer, thereby activating M and reducing i-type resistance. It can be p-type.
This is an action peculiar to gallium nitride-based compound semiconductor due to annealing.

By the way, in the case of forming an electrode of a semiconductor light emitting device having a pn junction, after adhering various electrode materials to the p-type layer and the n-type layer, the purpose is to alloy the electrode material, or the semiconductor layer. The semiconductor light emitting device may be annealed at several hundred degrees for the purpose of improving ohmic contact between the electrode and the electrode material. Due to the annealing at the time of forming the electrode, the above-mentioned action appears especially in the gallium nitride-based compound semiconductor. That is, when annealing, p
In the process in which hydrogen atoms bonded to the type dopant come out, first, thermal dissociation occurs due to annealing, and MH
The bond of is released. Next, the hydrogen dissociated by diffusion reaches the surface of the i-type GaN layer 4 where there is no p-type electrode 6, and is released to the outside.

However, as shown in FIG. 4, i-type GaN is used.
When a wide electrode is conventionally deposited on the layer 4, hydrogen dissociated from the p-type dopant in the i-type GaN layer 4 during the annealing is blocked by the upper electrode and does not come out. In particular, since hydrogen under the electrode does not flow out, the i-type GaN layer 4 directly below the electrode remains in the high resistance region. On the other hand, as shown in FIG. 3, when an electrode having a width of 20 μm or less is attached, hydrogen is generated in the i-type GaN layer 4 directly below the electrode.
It becomes possible to get out of, and becomes the p-type with a low resistance as a whole. That is, it can be estimated that the diffusion distance of hydrogen contained in the i-type GaN layer 4 is within about 10 μm.

Further, FIG. 7 shows that Ga is formed on a sapphire substrate.
When a wafer having an N buffer layer and an Mg-doped i-type GaN layer grown thereon was placed in an annealing apparatus and annealed in a nitrogen atmosphere for 10 minutes, the annealing temperature and the resistance of the i-type GaN layer after annealing were measured. It is a figure which shows the relationship with a rate. As shown in this figure, the resistivity of the i-type GaN layer sharply decreases from around 400 ° C.,
When the temperature exceeds 700 ° C., the value becomes almost constant and the resistance becomes p-type. Therefore, the annealing temperature is 400 ° C. or higher, more preferably 700 ° C. or higher. Further, the annealing atmosphere is preferably performed in an atmosphere containing no hydrogen. This is because hydrogen may be re-occluded in the i-type GaN layer and become high in resistance.

Therefore, in the electrode forming method of the present invention,
An electrode having a width of 20 μm or less is deposited on the i-type GaN layer 4 by vapor deposition, sputtering, or the like, and then annealed at 400 ° C. or more, so that the i-type GaN layer 4 has a low resistance p-type at the same time, and at the same time p-type. The electrode 6 and the GaN layer 4 that has changed to the p-type are in ohmic contact with each other, and a current easily flows.

[0015]

The present invention will be described in detail below with reference to FIGS. 5 and 6. FIG. 5 is a plan view of a chip having a GaN layer on which a p-type electrode is formed according to an embodiment of the present invention as viewed from the electrode side, and FIG. 6 is a partially enlarged view of the p-type electrode 6 of FIG. FIG.

[Example 1] 2 inch φ which is a transparent substrate
The GaN buffer layer 2 was grown to a film thickness of 200 angstroms on the C-plane of the sapphire substrate 1 using a MOCVD apparatus, and the Si-doped n-type GaN layer 3 having a film thickness of 4 μm was formed on the GaN buffer layer 2. On the n-type GaN layer 3, i-type Ga doped with Mg is grown.
The N layer 4 is grown. Further, a stripe-shaped p-type electrode 6 having a width of 20 μm is formed on the i-type GaN layer 4, and n-type G
The n-type electrode 5 is formed on the aN layer. Hereinafter, a method for forming the n-type electrode 5 and the p-type electrode 6 will be described in detail.

A protective film having a predetermined pattern is formed on the i-type GaN layer 4 by a photolithography technique. A part of the i-type GaN layer 4 is etched until the n-type GaN layer 3 is exposed. After the etching is completed, the protective film is peeled off, and a stripe-shaped p-type electrode pattern and a plane-shaped n-type electrode pattern are formed with a photoresist as shown in FIG. Al is deposited on the n-type GaN layer 3 and the p-type GaN layer 4 is formed.
Then, Au / Ni is vapor-deposited to form an n-type electrode 6 and a p-type electrode 5, respectively. The p-type electrode is formed by forming stripes having a width of 20 μm at intervals of 10 μm to form 16 stripes. After forming both electrodes, the wafer is annealed at 700 ° C. for 10 minutes in a nitrogen atmosphere. After the annealing, in order to electrically connect the p-type electrode 5, as shown in FIG.
A conductive material 7 such as n or Al is deposited.

After the electrodes 5 and 6 are formed as described above, the wafer is cut into 1 × 0.8 mm square chips to emit light as a light emitting diode.
Forward voltage 4V, peak wavelength 430n at 0 mA
The emission output was 60 μW.

[Embodiment 2] Embodiment 1 is different from Embodiment 1 except that the width of the p-type electrode 6 is 15 μm, the stripe interval is 15 μm, and the number is 16.
When the wafer was processed in the same manner as described above to form a light emitting diode, the forward current was 20 mA, the forward voltage was 4 V,
The light emission output was 60 μW, which was equivalent to that in Example 1.

Comparative Example 1 The width of the p-type electrode 6 is 25 μm,
Example 1 except that the stripe interval is 5 μm and the number is 16
When a wafer was processed in the same manner as described above to form a light emitting diode, the forward voltage was 5 V and the light emission output was 30 μW at the same forward current of 20 mA.

Comparative Example 2 The width of the p-type electrode 6 is 30 μm,
A wafer was processed into a light emitting diode in the same manner as in Example 1 except that the stripe spacing was 10 μm and the number of lines was 12, and the forward voltage was 7 V and the light emission output was 10 μW at the same forward current of 20 mA.

[Comparative Example 3] The width of the p-type electrode 6 is 50 μm,
Example 1 except that the stripe interval is 10 μm and the number is 8
When a wafer was processed in the same manner as described above to form a light emitting diode, the forward voltage was 10 V and the light emission output was 5 μW at the same forward current of 20 mA.

[0023]

As described above, in a gallium nitride compound semiconductor having a p-type electrode having a width of 20 μm or less, the entire i-type gallium nitride compound semiconductor layer becomes p-type with low resistance by annealing. Therefore, when it is used as a light emitting element, the light emitting characteristics thereof are almost equal and excellent. On the other hand, when a p-type electrode having a width of more than 20 μm is formed, a high resistance layer remains below the electrode, resulting in insufficient light emission characteristics. Moreover, the characteristics tend to deteriorate as the electrode width increases.

Therefore, by using the electrode forming method of the present invention, an excellent p-type gallium nitride-based compound semiconductor including an electrode can be realized, and its industrial utility value is great.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a structure of a conventional LED element.

FIG. 2 is a plan view of the element of FIG. 1 viewed from the electrode side.

FIG. 3 is a partial cross-sectional view showing a structure of an i-type GaN layer on which a p-type electrode is formed according to an embodiment of the present invention.

FIG. 4 i-type GaN having a p-type electrode formed by a conventional method
The partial cross section figure which shows the structure of a layer.

FIG. 5 is a plan view of a chip having a GaN layer on which a p-type electrode is formed according to an embodiment of the present invention, as viewed from the electrode side.

FIG. 6 is an enlarged cross-sectional view of a part of the electrode 6 of FIG.

FIG. 7 is a diagram showing the relationship between the annealing temperature and the resistivity of the i-type GaN layer after annealing.

[Explanation of symbols]

1 ... Substrate 2 ... Buffer layer 3 ... n-type GaN layer 4 ... i-type GaN layer 5 ... n-type electrode 6 ... p-type electrode 7 ... Conductive material

Claims (2)

[Claims] 1. A gallium nitride-based compound semiconductor, characterized in that an electrode having a width of 20 μm or less is formed on the gallium nitride-based compound semiconductor doped with a p-type dopant by ohmic contact by annealing. . 2. A gallium nitride-based compound semiconductor doped with a p-type dopant is deposited with an electrode having a width of 20 μm or less, and then the gallium nitride-based compound semiconductor is deposited with a thickness of 40 μm.
A method for forming an electrode of a gallium nitride-based compound semiconductor, which comprises annealing at 0 ° C. or higher.