JPH06314823A - Gallium nitride compound semiconductor light emitting element and its manufacture - Google Patents

Abstract

PURPOSE:To provide a light emitting diode of a GaN compound semiconductor with high luminance and high reliability and a manufacturing method thereof. CONSTITUTION:An i-layer on an n-layer has a double layer structure wherein a low impurity concentration iL-layer 5 and a high impurity concentration iH- layer 6 are formed. Pit (hole) parts 6a of various sizes are generated in a crystal surface of the high impurity concentration iH-layer 6. An insulation film 9 is formed in the pit part 6a by anode oxidation. Therefore, a current made to flow from an electrode 7 does not concentrate in the pit part 6a and luminance deterioration in a light emitting diode 10 based on local breakdown of the i-layer can be prevented. A light emitting diode having high luminance and high reliability can be acquired in this way.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a blue light emitting gallium nitride compound semiconductor light emitting device and a method for manufacturing the same.

[0002]

2. Description of the Related Art Conventionally, GaN has been used as a blue light emitting diode.
There are known ones using a system compound semiconductor. That G
Attention has been paid to the fact that an aN 2 -based compound semiconductor has a high emission efficiency because it is a direct transition, and that blue, which is one of the three primary colors of light, is the emission color. A light emitting diode using such a GaN-based compound semiconductor has a high carrier concentration n ⁺ layer made of an n-conductivity type GaN-based compound semiconductor, either directly on a sapphire substrate or with a buffer layer made of aluminum nitride interposed. A low carrier concentration n layer and an i layer in which a p-type impurity is added on the low carrier concentration n layer,
I _L layer added a small amount of p-type impurities specifically (hereinafter low as impurity concentration i _L layer) i _H layer added more than a low impurity concentration i _L layer (hereinafter, referred to as the high impurity concentration i _H layer)
And has a grown structure (JP-A-3-2521).
77 publication).

[0003]

As described above, the i-GaN layer before the formation of the i-layer electrode has a low impurity concentration i _L.
It has a double layer structure of a layer and a high impurity concentration i _H layer. In the film formation process of this double layer, the film growth temperature was 1150 in the former case.
In order to achieve a high impurity concentration, the temperature is set to ℃ and the impurity concentration is lowered to 900 ° C. A light-emitting diode having an i-layer electrode formed on the surface of a high impurity concentration i _H layer has a problem that luminance deterioration occurs in some lots after about 1000 hours in a room temperature continuous test (current value: 20 mA).

As a result of intensive studies and researches on the above-mentioned problems, the inventors have found out the cause of this phenomenon, and have found a GaN-based compound semiconductor light emitting diode having a novel structure and a method for manufacturing the same as follows. It has been provided. As the above-mentioned factor, due to the discontinuity of the crystalline state of the i-layer, defects called polygonal (hexagonal) pyramid-shaped pits (holes) are usually formed on the surface of the high impurity concentration i _H layer side where the electrodes are formed. A part will be formed. Then, in the region where the electrode of the i layer is formed, the polygonal pyramid is formed and the diagonal line of the bottom surface is about 1
If there is a large pit portion of 50 nm or more, current concentration occurs in that pit portion, and more current flows than the surroundings. As a result, the light emission intensity of the light emitting diode is lowered in total and the MIS (Metal Insulator Semic)
The onductor) structure is gradually destroyed locally from the pit portion, resulting in deterioration of the light emission luminance due to deterioration of durability.

The present invention has been made to solve the above-mentioned problems, and its purpose is to achieve high brightness and
A highly reliable GaN compound semiconductor light emitting diode and a method of manufacturing the same.

[0006]

The first feature of the constitution of the invention for solving the above-mentioned problems is that an n-type gallium nitride-based compound semiconductor (In _X Al _Y Ga _1-XY N; X = 0, Y =
0 layer) and an i-type gallium nitride-based compound semiconductor (In _X Al _Y Ga _{1 -XY} N;
In the gallium nitride-based compound semiconductor light-emitting device having an i layer formed of X = 0 and Y = 0), an insulating film is selectively provided only in at least a pit portion on the crystal surface of the i layer.

A second feature is that an n layer made of an n-type gallium nitride compound semiconductor (In _x Al _Y Ga _1-XY N; including X = 0 and Y = 0) and a p-type impurity are included. Added i-type gallium nitride compound semiconductor (In _X Al _Y Ga _1-XY N; X =
0, Y = 0) and an i-layer made of n).
Before forming an electrode on the i-layer and the i-layer, an insulating film is selectively formed only on at least a pit portion formed on the crystal surface of the i-layer.

[0008]

The GaN-based compound semiconductor light emitting diode of the present invention has an insulating film selectively in at least the pit portion of the crystal surface of the i layer so that current concentration does not occur in this pit portion. You can Therefore, without increasing the resistance of the device more than necessary, durability deterioration due to local destruction due to current concentration in the pit portion is prevented, and a gallium nitride-based compound semiconductor light emitting device having high brightness and high reliability, and This is the manufacturing method.

[0009]

EXAMPLES The present invention will be described below based on specific examples. FIG. 1 is a sectional view showing a GaN compound semiconductor light emitting diode 10 according to the present invention. Incidentally, FIG.
The cross section of the multilayer structure of the light emitting diode is shown in (a), and the enlarged cross section of the pit portion is shown in FIG. 1 (b). Light emitting diode 10
Has a sapphire substrate 1, and a 500 Å buffer layer 2 of AlN is formed on the sapphire substrate 1. On the buffer layer 2, a film thickness of 2.2 μm,
High carrier concentration n ⁺ layer 3 and the film thickness 1.1μm of GaN of carrier concentration 1.5 × 10 ¹⁸ / cm ^3, the carrier concentration of 1 × 10 ¹⁵
A low carrier concentration n-layer 4 made of GaN of / cm ³ is formed, and a film thickness of 1.1 μm is formed on the low carrier concentration n-layer 4.
A low impurity concentration i _L layer 5 made of GaN having m and Zn concentrations of 2 × 10 ¹⁸ / cm ^{3 and} a high impurity concentration i _H layer 6 made of GaN having a film thickness of 0.2 μm and Zn concentration of 1 × 10 ²⁰ / cm ³ are formed. Has been done. Then, an electrode 7 formed of aluminum and connected to the i _H layer 6 and an electrode 8 formed of aluminum and connected to the high carrier concentration n ⁺ layer 3 are formed.

Next, a method of manufacturing the light emitting diode 10 having this structure will be described. The light emitting diode 10 was manufactured by vapor phase epitaxy by a metal organic compound vapor phase epitaxy method (hereinafter referred to as MOVPE). The gas used is N
H ₃ and carrier gas H ₂ and trimethylgallium (Ga (C
H _{3) 3)} (hereinafter referred to as TMG) and trimethylaluminum _{(Al (CH 3) 3)} ( hereinafter referred to as TMA) and silane (Si
H ₄₎ and diethyl zinc (hereinafter, it is referred to as DEZ).

First, a single crystal sapphire substrate 1 whose main surface is the a-plane cleaned by organic cleaning and heat treatment is MOVP.
E Attach to the susceptor placed in the reaction chamber of the device. Next, the sapphire substrate 1 was vapor-phase etched at a temperature of 1100 ° C. while flowing H ₂ at a flow rate of 2 l / min into the reaction chamber under normal pressure. Next, the temperature is lowered to 400 ° C. and H ₂ is added at 20 l / min and N 2
H ₃ was supplied at 10 l / min and TMA was supplied at 1.8 × 10 ⁻⁵ mol / min to form a buffer layer 2 made of AlN having a thickness of 500 Å.

Next, the temperature of the sapphire substrate 1 is maintained at 1150 ° C., H ₂ is 20 l / min, NH ₃ is 10 l / min, and TMG is
Silane (SiH ₄ ) diluted to 1.76 × 10 ^-4 mol / min and 0.86 ppm with H ₂ was supplied at a rate of 200 ml / min for 30 minutes to obtain a film thickness.
2.2 .mu.m, to form a high-carrier density n ⁺ layer 3 made of GaN of carrier concentration 1.5 × 10 ¹⁸ / cm ^3.

Then, the temperature of the sapphire substrate 1 is set to 1150 ° C.
, H ₂ at 20 l / min, NH ₃ at 10 l / min, TMG
Was supplied at a rate of 1.7 × 10 ^-4 mol / min for 15 minutes to obtain a film thickness of 1.1
A low carrier concentration n layer 4 made of GaN having a carrier concentration of 1 × 10 ¹⁵ / cm ³ was formed.

Next, the sapphire substrate 1 is heated to 1150 ° C.,
H ₂ 20 l / min, NH ₃ 10 l / min, TMG 1.7 × 10
^-4 mol / min, DEZ at a rate of 1.5 × 10 ^-4 mol / min for 15 minutes, and a Zn concentration of 2 μm consisting of GaN with a film thickness of 1.1 μm 2
A low impurity concentration i _L layer 5 of × 10 ¹⁸ / cm ³ was formed.

Subsequently, the sapphire substrate 1 is heated to 900 ° C., H ₂ is 20 l / min, NH ₃ is 10 l / min, and TMG is 1.7 l.
× 10 ^-4 mol / min, DEZ was supplied at a rate of 1.5 × 10 ^-4 mol / min for 3 minutes, and a high impurity concentration i _{H of} Zn concentration 1 × 10 ²⁰ / cm ³ consisting of GaN with a film thickness of 0.2 μm Layer 6 was formed. In this way, a wafer having a multilayer structure as shown in FIG. 2 was obtained.

After completion of the above-mentioned crystal growth, the surface of the high impurity concentration i _H layer 6 in the formed multi-layered wafer is
As shown in the enlarged cross section of FIG. 3, a pit portion 6a is formed. This pit portion 6a has a high impurity concentration i _H
It appears in various sizes on the surface of the layer 6, and as described above, if the diagonal line of the polygonal pyramid-shaped bottom surface is about 150 nm or more, the deterioration of the emission intensity is greatly affected. A metal serving as a positive pole is vapor-deposited on a part of the periphery of the high impurity concentration i _H layer 6 having the pit portion 6a in the wafer having the multilayer structure. Then, except for the surface of the high impurity concentration i _H layer 6 on which the metal is not vapor-deposited, an insulating material such as apiezon wax is applied to the entire periphery of the wafer having the above-mentioned multilayer structure. That is, to expose only the i _H -GaN surface. In the above embodiment, an example of apiezon wax is shown, but it is sufficient that the wafer except the surface of the high impurity concentration i _H layer 6 where the metal is not vapor-deposited is electrically insulated by an appropriate jig. Then, as shown in FIG. 4, the metal portion deposited on the wafer having the above-mentioned multi-layer structure was used as a positive electrode and the Pt electrode was used as a negative electrode, and a 9 wt% H ₂ SO ₄ aqueous solution was used as an electrolytic solution. Connected to construct an anodizing device consisting of a closed circuit. In the anodizing apparatus described above, an anode containing gallium oxide pits 6a of the i _H -GaN surface by current density anodizing by supplying a constant current of 10 .mu.A / cm ² while stirring the aqueous H ₂ SO ₄ An insulating film 9 which is an oxide film was formed. The H ₂ SO ₄ aqueous solution concentration can be set in the range of 1 to 20 wt% and the current density can be set in the range of 1 to 100 μA / cm ² . Further, as the electrolytic solution, an H ₂ SO ₄ aqueous solution, a H ₂ O ₂ solution, or the like can be used. In addition to the anodic oxide film containing gallium oxide by the above-mentioned anodic oxidation as the insulating film 9, another metal such as aluminum (Al) is selectively attached to the pit portion 6a by electroplating or the like to be oxidized. You may form by.

Next, as shown in FIG. 6, a SiO ₂ layer 11 is sputtered on the high impurity concentration i _H layer 6.
Formed to a thickness of 2000Å. Next, a photoresist 12 was applied on the SiO ₂ layer 11, and the photoresist 12 was formed by photolithography in a pattern in which the photoresist at the electrode formation site for the high carrier concentration n ⁺ layer 3 was removed. Next, as shown in FIG. 7, the SiO ₂ layer 11 not covered with the photoresist 12 was removed with a hydrofluoric acid-based etching solution.

Next, as shown in FIG. 8, the high impurity concentration i _H layer 6 and the low impurity concentration i _L layer 5 thereunder are covered by the photoresist 12 and the SiO ₂ layer 11.
And a part of the upper surface of the low carrier concentration n layer and the high carrier concentration n ⁺ layer 3 are vacuum degree 0.04 Torr, high frequency power 0.44 W / cm ² , C
Cl ₂ F ₂ gas was supplied at a rate of 10 ml / minute for dry etching, and then Ar was used for dry etching. Next, as shown in FIG. 9, S remaining on the high impurity concentration i _H layer 6 is removed.
The iO ₂ layer 11 was removed with hydrofluoric acid.

Next, as shown in FIG. 10, the degree of vacuum is 8 ×
Hold at 10 ^-7 Torr and sample temperature 225 ℃,
An Al layer 13 was formed by vapor deposition. Then, a photoresist 14 is applied on the Al layer 13 and is subjected to a photolithography process so that the photoresist 14 has a predetermined electrode portion for the high carrier concentration n ⁺ layer 3 and the high impurity concentration i _H layer 6. The pattern was formed into a shape.

After the above manufacturing process, the photoresist 14 is formed.
The exposed portion of the Al layer 13 which is not covered by the etching is etched with a nitric acid-based etching solution, the photoresist 14 is removed with acetone, and the electrode 8 of the high carrier concentration n ⁺ layer 3 and the electrode 7 of the high impurity concentration i _H layer 6 are removed. Was formed. Here, the state of the insulating film 9 which is the anodic oxide film containing gallium oxide formed in the pit portion 6a of the high impurity concentration i _H layer 6 and the state of the electrode 7 thereon are shown in FIG. 1 (b). In this way, FIG.
The GaN-based compound semiconductor light emitting diode having the MIS structure shown in (a) can be manufactured. The metal material of the electrode 8 of the high carrier concentration n ⁺ layer 3 and the electrode 7 of the high impurity concentration i _H layer 6 is n ⁺ -Ga such as Ti in addition to Al.
Any metal substance capable of making ohmic contact with the N 3 layer 3 may be used.

As described above, even if the high impurity concentration i _H layer 6 on which the electrode 7 is formed has a large pit portion 6a, the large pit portion 6a is covered with the insulating film 9 and current does not concentrate at that portion. Therefore, the GaN-based compound semiconductor light emitting diode of the present invention has high brightness and MI.
Since the S structure is not locally locally destroyed and the emission intensity is not lowered, the S structure has high reliability. Further, in the above-mentioned embodiment, only GaN is described, but also in InGaAlN material, if there are pits, it is possible to selectively manufacture an insulating film which is an anodized film, and it is selected by an electroplating method. It is possible to form an insulating film such as a metal oxide. Therefore, this method is also effective for InGaAlN semiconductor systems.

[Brief description of drawings]

FIG. 1 is a configuration diagram illustrating a light emitting diode according to a specific embodiment of the present invention.

FIG. 2 is a partial cross-sectional view showing a wafer having a multilayer structure for forming the light emitting diode according to the embodiment.

FIG. 3 is a partially enlarged cross-sectional view showing a pit portion formed in a high impurity concentration i _H layer of a wafer having a multilayer structure of a light emitting diode according to the same example.

FIG. 4 is a configuration diagram showing an anodizing device used for manufacturing the light emitting diode according to the embodiment.

FIG. 5 is a partially enlarged cross-sectional view showing an insulating film formed by anodizing the pit portion of the high impurity concentration i _H layer of the wafer having the multilayer structure of the light emitting diode according to the example.

FIG. 6 is a cross-sectional view showing a manufacturing process of a wafer having a multilayer structure of a light emitting diode according to the same embodiment.

7 is a cross-sectional view subsequent to FIG. 6, showing a manufacturing process of a wafer having a multilayer structure of a light emitting diode according to the same example.

FIG. 8 is a cross-sectional view subsequent to FIG. 7, showing a manufacturing process of a wafer having a multilayer structure of a light emitting diode according to the same embodiment.

9 is a cross-sectional view following FIG. 8 showing a manufacturing process of a wafer having a multilayer structure of a light emitting diode according to the same embodiment.

10 is a cross-sectional view showing the manufacturing process of the wafer having the multi-layer structure of the light emitting diode according to the embodiment, following FIG. 9;

[Explanation of symbols]

1 ... Sapphire substrate 2 ... Buffer layer 3 ... High carrier concentration n ⁺ layer 4 ... Low carrier concentration n layer 5 ... Low impurity concentration i _L layer 6 ... High impurity concentration i _H layer 6a ... Pit (hole) part 7, 8 ... Electrode 9 ... Insulating film 10 ... Light emitting diode (gallium nitride compound semiconductor light emitting element)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Masafumi Hashimoto, Inventor, Masafumi Hashimoto, No. 41 Yokomichi, Nagakute-cho, Aichi-gun, Aichi-gun, Toyota Central Research Institute Co., Ltd.

Claims (2)

[Claims] 1. An n-type gallium nitride-based compound semiconductor (I
n _X Al _Y Ga _1-XY N; including X = 0 and Y = 0)
Layer and an i layer made of an i-type gallium nitride-based compound semiconductor (In _X Al _Y Ga _1-XY N; including X = 0 and Y = 0) doped with a p-type impurity In the light emitting device, a gallium nitride-based compound semiconductor light emitting device having an insulating film selectively in at least pits (holes) on the crystal surface of the i layer. 2. An n-type gallium nitride-based compound semiconductor (I
n _X Al _Y Ga _1-XY N; including X = 0 and Y = 0)
Layer and an i layer made of an i-type gallium nitride-based compound semiconductor (In _X Al _Y Ga _1-XY N; including X = 0 and Y = 0) doped with a p-type impurity In the method for manufacturing a light emitting device, an insulating film is selectively formed only on at least pits (holes) formed on a crystal surface of the i layer before forming electrodes on the n layer and the i layer. Method for manufacturing gallium compound semiconductor light emitting device.