JPH10284802A - Nitride-based compound semiconductor light emitting element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve crystallinity of a nitride-based compound semiconductor film by making the film thickness of a crystalline substrate of an element on which the nitride-based compound semiconductor film expressed by a specific formula is formed thinner than the thickness of the film thickness of the nitride- based compound semiconductor film. SOLUTION: A nitride-based compound semiconductor light emitting component which is provided with a nitride-based compound semiconductor film expressed by Al(1- X) GaXN (0<=X<=1) on a buffer layer formed on a crystalline substrate 1 is fabricated by forming an n-type GaN clad layer 2, an n-type InGa active layer 3, a p-type GaN clad layer 4, a p-type electrode 5 on the sapphire substrate 1 in sequence. The film thickness of the substrate 1 is set to e.g. approximately 50 μm, while the film thickness of the n-type GaN clad layer 2 is set to e.g. approximately 60 μm. Because of such a construction, the strain caused by the difference in thermal expansion coefficient is selectively made to occur at the crystalline substrate so that the crystallinity of the nitride- based compound semiconductor formed on the crystalline substrate can be enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a nitride compound semiconductor light emitting device used for a short wavelength light source or the like.

[0002]

2. Description of the Related Art In recent years, GaN (gallium nitride), In
Nitride-based compound semiconductors such as N and AlN are of a direct transition type in which the minimum point of the conduction band and the maximum point of the valence band are located at wave numbers close to each other, and have a wide energy gap. It is in the spotlight as a material for environmentally-friendly devices. For example, GaN is about 3.4e at room temperature.
It has a wide energy gap of V and is a promising material for light emitting devices in the blue to ultraviolet region.

In general, metal-organic vapor phase vapor deposition (hereinafter referred to as MOCVD) is used to form a nitride-based compound semiconductor crystal. For example, in the case of forming a GaN crystal, trimethylgallium and ammonia are used as raw materials, and Ga obtained by decomposing trimethylgallium on a substrate heated to a high temperature and N obtained by decomposing ammonia are used. A single crystal GaN film is grown.

At present, a sapphire substrate is generally used as a substrate on which a GaN-based compound semiconductor crystal is formed. However, the lattice constant of the sapphire substrate is a =
4.76 ° and c = 12.99 °, whereas GaN
The lattice constants of the crystals are a = 3.19 ° and c = 5.19 °, and MOCV
During film growth by the D method, stacking faults of 10 ¹⁰ cm ⁻³ or more occur in GaN from the interface between the sapphire substrate and the GaN crystal. Further, since the sapphire substrate and the GaN crystal have different coefficients of thermal expansion, defects may grow in the GaN crystal during the temperature rising / falling routine between room temperature and a high temperature of 1000 ° C. or more in MOCVD, Cracks occur.
That is, the GaN crystal grown on the sapphire substrate has poor crystallinity.

Therefore, as a technique widely used at present, there is a method of introducing a buffer layer between a sapphire substrate and a GaN crystal. By this method, stress due to lattice mismatch between the sapphire substrate and the GaN crystal is reduced,
The occurrence of stacking faults is suppressed. In addition, stress due to a difference in thermal expansion coefficient at the time of temperature rise and fall is alleviated, and defect growth and crack generation in the GaN crystal are suppressed.

As a buffer layer, Japanese Patent Application Laid-Open No. 4-29702
As described in Japanese Patent Application Publication No. 3 (1994), it is very effective to use a GaN film, and when a light emitting diode is manufactured using this technique, the luminance is ten times or more that of a conventional light emitting diode. Has been confirmed to be obtained.

FIG. 4 shows an example of the structure of a light-emitting diode which is an example of a nitride-based compound semiconductor light-emitting device manufactured by using a conventional technique.

The method for manufacturing this light emitting diode is as follows. An n-type GaN cladding layer 12 is formed on a sapphire
The GaN active layer 13 and the p-type GaN clad layer 14 are sequentially formed to form a double hetero junction (DH) structure. Next, a p-type electrode 15 is formed, a mask is aligned, and etching is performed. Finally, an n-type electrode 16 is formed on the etched portion of the n-type GaN clad layer 12. Here, the thickness of the sapphire substrate 11 is 150 μm, and the n-type GaN cladding layer 12 is
Is 50 μm.

[0009]

However, the above-mentioned conventional nitride-based compound semiconductor light-emitting device has the following problems.

[0010] That is, by introducing a buffer layer between the crystal substrate and the nitride-based compound semiconductor film, the occurrence of stacking faults and cracks can be suppressed. Stacking faults of about ¹⁰ cm ^-3 exist. For example, when an element is manufactured in this state, a leak current is generated, and light emission failure or element destruction occurs due to a decrease in quantum efficiency. In particular, when stacking faults are introduced into the light-emitting portion, the device breaks down at an accelerated rate and the life of the device is significantly reduced.

An object of the present invention is to provide a nitride-based compound semiconductor light emitting device which can solve the above-mentioned problems of the prior art and can suppress the growth of defects and the occurrence of cracks in the nitride-based compound semiconductor film. is there.

[0012]

According to the present invention, a nitride-based compound semiconductor light emitting device is provided on a crystal substrate or a buffer layer formed on the crystal substrate, by forming an Al _(1-X) Ga _X N (0 ≦ X ≤
A nitride-based compound semiconductor light-emitting device having a nitride-based compound semiconductor film represented by 1), wherein the thickness of the crystal substrate is smaller than the thickness of the nitride-based compound semiconductor film. .

With this configuration, the strain accompanying the temperature rise and fall during the formation of the nitride-based compound semiconductor film is selectively generated on the crystal substrate side, thereby suppressing the growth of defects and the generation of cracks in the nitride-based compound semiconductor film. Becomes possible.

In the present invention, it is preferable that the thickness of the crystal substrate is smaller than the thickness of the nitride-based compound semiconductor film by 10 μm or more.

According to this structure, the strain accompanying the temperature rise and fall during the formation of the nitride-based compound semiconductor film is selectively generated on the crystal substrate side, thereby preventing the growth of defects and the generation of cracks in the nitride-based compound semiconductor film. Becomes possible. In particular, it is effective in a process that requires a high-temperature film formation process of 1000 ° C. or more by the MOCVD method.

[0016]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a structural view of a light emitting diode according to the present invention. On a sapphire substrate 1, an n-type GaN cladding layer 2, an n-type InGaN active layer 3, a p-type GaN cladding layer 4, and a p-type electrode 5 are sequentially laminated. Also, n
An n-type electrode 6 is also formed on the type GaN cladding layer 2.
The fabrication method is the same as the conventional procedure, but the sapphire substrate 1
Is 50 μm, and the thickness of the n-type GaN cladding layer 2 is 6 μm.
0 μm. The thickness of the sapphire substrate 1 is 1/3 that of the conventional example, and 10 μm smaller than the thickness of the n-type GaN cladding layer 2. With this configuration, distortion due to a difference in thermal expansion coefficient can be selectively generated on the crystal substrate side, and the crystallinity of the nitride-based compound semiconductor film formed on the crystal substrate can be improved.

FIG. 2 shows a sapphire substrate (150 μm thick).
m) An undoped GaN crystal (50 μm thick) formed on
FIG. 3 is a diagram comparing the carrier concentration of an undoped GaN crystal (thickness: 60 μm, sample 2) formed on a sapphire substrate (thickness: 50 μm) with a carrier concentration of m, sample 1). Sample 1 has a carrier concentration of 10 ¹⁸ cm ^-3
In contrast, the carrier concentration of Sample 2 was 10 ¹⁵ c
m ⁻³ or less. This indicates that in Sample 2, the number of crystal defects acting as donors was significantly reduced. That is, it is understood that the crystallinity of GaN is improved in Sample 2. The same result can be obtained by replacing the undoped GaN crystal with the n-type GaN crystal according to the present invention.

FIG. 3 is a diagram comparing the emission spectra of the respective samples of FIG. The spectrum of Sample 1 (curve A) shows that, besides the band edge emission (350 to 425 nm), 45
While broad emission appears at a wavelength of 0 to 700 nm, such broad emission does not appear in the emission spectrum of the sample 2 (curve B). This broad light emission is due to crystal defects, indicating that undoped GaN has poor crystallinity. In the emission spectrum of Sample 2, such broad light emission has disappeared, indicating that Sample 2 has improved crystallinity of GaN. This also means that undoped GaN crystals can be converted to n-type GaN.
Similar results can be obtained by replacing the crystal.

As apparent from the evaluation results shown in FIGS. 2 and 3, as described above, in the light emitting diode according to one embodiment of the present invention, the thickness of the crystal substrate is smaller than that of the nitride-based compound semiconductor film. This indicates that the growth of crystal defects and the generation of cracks in the nitride-based compound semiconductor film are significantly suppressed.

In the present invention, a conductive crystal substrate other than a sapphire substrate or an insulating crystal substrate may be used as the crystal substrate.

For forming the nitride-based compound semiconductor film and the buffer layer, an epitaxial growth method other than the MOCVD method, such as a liquid phase epitaxial growth method, a vapor deposition method, or a molecular beam epitaxial growth method, can be used.

In addition, a buffer layer other than GaAs II
A single-layer or multiple-layer I / V compound semiconductor thin film, II / VI compound semiconductor thin film, oxide thin film, or metal thin film can be used.

[0024]

As described above, according to the present invention,
Crystalline nitride compound semiconductor film represented by formed on the crystal substrate or a buffer layer formed on the crystal substrate _{Al (1-X) Ga X} N (0 ≦ X ≦ 1) is excellent, emission It is possible to provide a nitride-based compound semiconductor light-emitting device free from defects and device destruction.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a light-emitting diode according to an embodiment of the present invention.

FIG. 2 is a comparison diagram of carrier concentration depending on the film thickness of a sapphire substrate and a GaN crystal.

FIG. 3 is a comparison diagram of emission spectra depending on the film thickness of a sapphire substrate and a GaN crystal.

FIG. 4 is a cross-sectional view of a conventional light emitting diode.

[Explanation of symbols]

 Reference Signs List 1 sapphire substrate 2 n-type GaN cladding layer 3 n-type InGaP active layer 4 p-type GaN cladding layer 5 p-type electrode 6 n-type electrode

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tadahiro Hashimoto 1-1, Yukicho, Takatsuki-shi, Osaka Matsushita Electronics Industrial Co., Ltd. (72) Inventor Masahiro Ishida 1-1-1, Yukicho, Takatsuki-shi, Osaka Matsushita Electronics Industrial Co., Ltd. (72) Inventor Takashi Sugino Room 322, 3-4-1, Kamishinta, Toyonaka-shi, Osaka

Claims (2)

[Claims] To 1. A on the crystal substrate or a buffer layer formed on the crystal _{substrate, Al (1-X) Ga} X N (0 ≦ X ≦ 1)
A nitride-based compound semiconductor light-emitting device formed with a nitride-based compound semiconductor film represented by the formula: wherein the thickness of the crystal substrate is smaller than the thickness of the nitride-based compound semiconductor film. Based compound semiconductor light emitting device. 2. The nitride-based compound semiconductor light-emitting device according to claim 1, wherein the thickness of the crystal substrate is smaller than the thickness of the nitride-based compound semiconductor film by 10 μm or more.