JP2836687B2 - Gallium nitride based compound semiconductor light emitting device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a general formula _{In X Al Y Ga 1-XY} N (0 ≦ X <1,0 ≦ Y <1) a gallium nitride compound semiconductor represented by is laminated on a sapphire substrate The present invention relates to a gallium nitride-based compound semiconductor light emitting device and a method for manufacturing the same.

[0002]

2. Description of the Related Art GaN, GaAlN, InGaN, In
Gallium nitride-based compound semiconductors such as AlGaN have direct transitions, change their band gaps from 1.95 eV to 6 eV, and their emission colors range from ultraviolet to red. Therefore, materials for light-emitting elements such as light-emitting diodes and laser diodes Promising as. The light emitting device made of the gallium nitride-based compound semiconductor is generally formed on a sapphire substrate using n-type and p-type by vapor phase growth methods such as MOCVD and MBE.
Alternatively, it is obtained by growing and stacking into n-type and i-type, taking out the electrodes from each layer, fixing them in a chip shape to a lead frame, and finally sealing them with a resin such as epoxy.

However, the gallium nitride-based compound semiconductor light-emitting device has a so-called heteroepitaxial structure in which a completely different material of a gallium nitride-based compound semiconductor is stacked on a sapphire substrate as described above. As compared with a light emitting element stacked on the same material, there is a disadvantage that external quantum efficiency is deteriorated due to a difference in refractive index between the substrate and the epitaxial film. Specifically, due to the difference in the refractive index between the sapphire substrate and the gallium nitride-based compound semiconductor, and the difference in the refractive index between the gallium nitride-based compound semiconductor element and the resin that seals it, light emission of the gallium nitride-based compound semiconductor is There is a problem that the reflected light is absorbed inside the gallium nitride-based compound semiconductor and the emitted light cannot be efficiently extracted to the outside.

[0004]

SUMMARY OF THE INVENTION The multiple reflection between a gallium nitride compound semiconductor, a substrate, and a sealing resin is suppressed,
If the interference can be reduced, the external quantum efficiency can be improved and the luminous efficiency can be improved. Therefore,
The present invention has been made in view of such circumstances, and an object of the present invention is to suppress interference caused by multiple reflection of light inside a gallium nitride-based compound semiconductor, thereby achieving a gallium nitride-based compound semiconductor light-emitting device. It is to improve external quantum efficiency.

[0005]

In order to suppress the multiple reflection inside the gallium nitride-based compound semiconductor and to increase the external quantum efficiency, we conducted various experiments. It has been newly found that the above problem can be solved by irregular reflection at the interface of the compound semiconductor. That is, in the gallium nitride-based compound semiconductor light-emitting device of the present invention, a gallium nitride-based compound semiconductor layer serving as a light-emitting device is grown on an off-substrate of the sapphire substrate C plane (0001), and the uppermost layer of the gallium nitride-based compound semiconductor is formed. Is characterized in that the surface is non-mirror. It is preferable that the angle of the off-substrate is 0.2 ° or more and 15 ° or less with respect to the sapphire C plane.

FIG. 1 is a schematic sectional view of a gallium nitride based compound semiconductor light emitting device according to one embodiment of the present invention. This light emitting device has an n-type GaN layer 2 on a sapphire substrate 1,
p-type or high-resistance i-type GaN layer 3 (hereinafter referred to as p-type GaN
), And a part of the p-type GaN layer is etched to expose the n-type GaN layer.
An electrode is formed on the layer and the p-type GaN layer. Further, the surface of the uppermost p-type GaN layer on which an electrode is formed is made non-mirror. In the gallium nitride-based compound semiconductor light emitting device having this structure, the emission observation surface is on the sapphire substrate 1 side.

FIG. 2 is a schematic sectional view of a gallium nitride based compound semiconductor device according to another embodiment of the present invention. This is also structurally similar to FIG. 1 except that the uppermost p-type GaN layer 3 forming an electrode is also non-mirror, but this light-emitting element has a light emission observation surface on the p-type GaN layer 3 side. ing.

As shown in these figures, in order to make the uppermost layer of the gallium nitride-based compound semiconductor non-mirror surface, that is, a state in which fine irregularities are formed, first, the uppermost layer is made non-mirror surface during growth. And second, a method in which the uppermost layer after the growth is made non-specular by a chemical or physical method. The first method uses a gallium nitride-based compound semiconductor on a sapphire substrate C
This is a method of laminating on the off substrate from the plane (0001). The gallium nitride-based compound semiconductor is usually grown and laminated on the C-plane of the sapphire substrate, and by growing on the C-plane, a gallium nitride-based compound semiconductor having the uppermost layer as a mirror surface is obtained. However, in the method of the present invention, a gallium nitride-based compound semiconductor is deposited on an off-substrate from the C-plane, that is, a sapphire substrate whose angle is shifted from the C-plane by several degrees.
By performing step growth to form a p-type or p-type or i-type and stacking them, the uppermost gallium nitride-based compound semiconductor can be made non-mirror. The angle (offset angle) of the off-substrate is 0.2 ° or more with respect to the C-plane of sapphire.
5 ° or less is preferred. If the angle is smaller than 0.2 °, it is difficult to form a non-mirror surface.

On the other hand, the second method is a method in which fine irregularities are provided to make a non-mirror surface by etching or polishing the surface of the uppermost gallium nitride-based compound semiconductor having a mirror surface. For example, phosphoric acid +
There are two types of methods, wet etching using a mixed acid of sulfuric acid and dry etching using an apparatus such as RIE (reactive ion etching), and either method may be used.
By selecting an appropriate polishing agent for polishing, even a very hard gallium nitride-based compound semiconductor having a Mohs hardness of approximately 9 can be polished to make the surface non-mirror. that's all,
In the first method and the second method, it is preferable to make the first method non-specular. Because the second method is to physically or chemically forcibly damage the crystal, the first method damages the crystal because the top layer can be made non-mirror more naturally than during growth. Nothing. Therefore, even in the case of a light emitting element, the light emission intensity may be reduced in the second method, but is not at all concerned in the first method. In the first method, since the gallium nitride-based compound semiconductor is grown on the off-substrate from the beginning, an extra step can be omitted as in the second method, and the productivity is excellent.

[0010]

FIGS. 3 and 4 are schematic cross-sectional views showing optical paths of a conventional gallium nitride-based compound semiconductor light emitting device and a gallium nitride-based compound semiconductor light emitting device of the present invention in a light emitting state. The reference numerals given in these figures indicate the same substances as those in FIGS. In the light emitting device having this structure, the light emitting layer corresponds to the p-type GaN layer 3. Here, when the refractive index of sapphire is approximately 1.6 and the refractive index of the gallium nitride-based compound semiconductor is approximately 2, as shown in FIG. 3, the conventional light-emitting device includes a sapphire substrate 1, a gallium nitride-based compound semiconductor 2 Since the materials have different refractive indices, a part of the light emission of the p-type GaN layer 3 is at the interface between the p-type GaN layer 4 and the outside (in the case of a light-emitting diode, an epoxy resin is often used). The sapphire substrate 1 and the n-type G
Reflection at the interface with the aN layer 2 causes multiple reflections, which are gradually absorbed into the gallium nitride-based compound semiconductor layers 2 and 3 and attenuated. Since the n-type GaN layer 2 and the p-type GaN layer 3 are made of the same material and may have almost the same refractive index, the multiple reflection at the interface between the semiconductor layers may be regarded as zero (0). . On the other hand, when the p-type GaN layer 3, which is the uppermost layer, is non-specular as in the present invention in FIG. Since the light is scattered by the GaN layer, multiple reflection inside the gallium nitride-based compound semiconductor can be suppressed, and light interference can be reduced.

[0011]

[Example 1] A sapphire off-substrate shifted by 1 ° from the C-plane was prepared, and a GaN buffer layer, a Si-doped n-type GaN layer were formed thereon by MOCVD.
An Mg-doped p-type GaN layer is sequentially grown. Innumerable fine irregularities were formed on the surface of the p-type GaN layer thus grown. Next, a predetermined pattern is formed on this p-type GaN layer by photolithography technology,
After partially etching the n-type GaN layer to expose an n-type GaN layer only for forming an electrode, ohmic electrodes are attached to the p-type GaN layer and the n-type GaN layer. When current was applied to both electrodes, the emission spectrum of the gallium nitride-based compound semiconductor was measured. The spectrum was as shown in FIG. 5A, and had a peak at 400 nm.

On the other hand, for comparison, a conventional gallium nitride-based compound semiconductor light-emitting device similarly grown on the C-plane of a sapphire substrate was fabricated in the same manner, and its spectrum was measured. However, the spectrum was as shown by the broken line in FIG.

When comparing FIG. 5A and FIG. 5B, FIG.
Is near 410 nm besides the peak at 400 nm,
Weak peaks due to multiple reflection are observed around 430 nm and around 460 nm. On the other hand, in the case of (a), which is the spectrum of the light emitting device of the present invention, the peaks are not seen and the curve is broad, indicating that the multiple reflection is reduced. Moreover, the emission intensity is 1 in (a).
It has improved by 0% or more.

Example 2 A light emitting device was formed in the same manner as in Example 1 except that a sapphire off-substrate shifted from the C plane by 10 ° was used.
Light emission of almost the same intensity was observed.

Example 3 A GaN buffer layer, a Si-doped n-type GaN layer, and a Mg-doped p-type G were formed in the same manner as in Example 1 except that the GaN layer was grown on the C-plane of the sapphire substrate.
An aN layer was laminated. Further, the wafer on which the gallium nitride-based compound semiconductor was laminated was immersed in a mixed acid of phosphoric acid and sulfuric acid, and electrodes were provided in the same manner as in Example 1 except that the surface of the p-type GaN layer was made non-mirror, and the emission spectrum was measured. However, the same broad curve as in Example 1 was obtained, and the strength was reduced by about 10% as compared with Example 1.

[Embodiment 4] As in Embodiment 2, a GaN buffer layer, an n-type GaN layer, and a p-type Ga
The emission spectrum of the light emitting device was measured in the same manner as in Example 1 except that the p-type GaN layer of the wafer on which the N layer was grown was etched by RIE, and the surface was made non-mirror. Was obtained, and the strength was reduced by about 5% as compared with Example 1.

[0017]

As described above, the gallium nitride-based compound semiconductor device of the present invention has a non-mirror surface on the uppermost layer of the gallium nitride-based compound semiconductor. Light interference can be suppressed. Therefore, light emission of the gallium nitride-based compound semiconductor can be effectively extracted to the outside, and the external quantum efficiency of the light emitting element is improved. In addition, since a peak due to interference other than the intended emission peak does not appear in the emission spectrum, the color purity of a blue light-emitting diode manufactured using a gallium nitride-based compound semiconductor can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing the structure of a gallium nitride based compound semiconductor light emitting device according to one embodiment of the present invention.

FIG. 2 is a schematic sectional view showing the structure of a gallium nitride-based compound semiconductor device according to another embodiment of the present invention.

FIG. 3 is a schematic sectional view showing an optical path of a conventional gallium nitride based compound semiconductor light emitting device.

FIG. 4 is a schematic sectional view showing an optical path of a gallium nitride based compound semiconductor light emitting device according to one embodiment of the present invention.

FIG. 5 is a graph showing a comparison between emission spectra of a gallium nitride-based compound semiconductor light-emitting device according to one embodiment of the present invention and a conventional gallium nitride-based compound semiconductor light-emitting device.

[Explanation of symbols]

1 ... Sapphire substrate 2 ... N-type G
aN layer 3 p-type GaN layer

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-3-163883 (JP, A) JP-A-4-354382 (JP, A) JP-A-4-42582 (JP, A) 23868 (JP, B1) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 33/00 JICST file (JOIS)

Claims (2)

(57) [Claims] 1. A gallium nitride-based compound semiconductor layer serving as a light-emitting element is grown on an off-substrate on a C-plane (0001) of a sapphire substrate, and the surface of the uppermost layer of the gallium nitride-based compound semiconductor is non-mirror. A gallium nitride-based compound semiconductor light emitting device, comprising: 2. The gallium nitride-based compound semiconductor light emitting device according to claim 1, wherein the angle of the off-substrate is not less than 0.2 ° and not more than 15 ° with respect to a sapphire C plane.