KR20030089574A - Gallium Nitride-Based Compound Semiconductor - Google Patents

Abstract

The present invention relates to a gallium nitride-based light emitting device that improves the light emission efficiency, the gallium nitride-based light emitting device is n-type GaN buffer layer, n-type GaN layer, InGaN light-emitting layer, p-type GaN layer, n-type electrode on the sapphire substrate and p-type electrodes are formed in order. A ZnO transparent electrode is formed adjacent to the p-type electrode on the p-type GaN layer. The current is uniformly supplied to the light emitting layer by the ZnO transparent electrode, and simultaneously transmits light from the light emitting layer to the outside.

Description

Gallium nitride-based compound semiconductor device {Gallium Nitride-Based Compound Semiconductor}

TECHNICAL FIELD This invention relates to the improvement of a gallium nitride compound semiconductor device, especially luminous efficiency. Background Art In recent years, light emitting devices using gallium nitride (GaN) compound semiconductors have been known, and applications such as blue LEDs have become useful.

In FIG. 3, the structure of the light emitting element using the conventional GaN type compound semiconductor is shown. An n-type GaN buffer layer 12 is formed on the sapphire substrate 10, and a thin n-type GaN layer 14 is formed on the GaN buffer layer 12. As the light emitting layer, for example, an InGaN light emitting layer 16 is formed, and a p-type GaN layer 18 is formed thereon to form a PN junction. After the p-type GaN layer 18 is formed, part of the surface is etched to expose the surface of the n-type GaN buffer layer 12, and the n-type electrode 20 is formed on the n-type GaN buffer layer 12. The p-type electrode 22 is formed on the surface of the p-type GaN layer 18. By applying forward voltages to the p-type electrode 22 and the n-type electrode 20, carriers are injected into the InGaN light emitting layer 16, and a predetermined wavelength (blue) is emitted from the InGaN light emitting layer 16.

In the configuration of FIG. 3, since the current flows from the p-type electrode 22 toward the n-type electrode 20, and in particular, a large amount of current flows in the lower portion of the p-type electrode 22. The light emission is strongest at the bottom. However, light emitted from the InGaN light emitting layer 16 is blocked by the p-type electrode 22, and it is impossible to efficiently emit light emitted to the outside.

Therefore, it is proposed to form a metal p-type electrode 22 on the p-type GaN layer 18 and to form a transparent electrode. By forming the transparent electrode, the current can flow uniformly over almost the entire surface of the InGaN light emitting layer 16, instead of allowing the current to flow only under the p-type electrode 22, and also collect and emit light from the transparent electrode. By doing so, the luminous efficiency can be improved.

However, Ni / Au or ITO (Indium Tin Oxide) or the like is used as the transparent electrode. Since Ni / Au is a metal, the thickness of the electrode is good for current expansion, but the light transmittance is poor, and if the thickness of the electrode is thin, the current resistance is difficult to occur because the transmembrane resistance of the light is easily transmitted. there is a problem. In addition, ITO has a high light transmittance at a wavelength of 400 nm or more, but has an n-type conductivity and resistivity is not as small as that of metal, so that ohmic contact with the p-type GaN layer 18 is not good, and current does not flow uniformly. There is. In addition, ITO has a problem that etching is relatively difficult, and thus the shape of the etched pattern tip is easily damaged, and a desired shape cannot be obtained when processing as an electrode.

An object of the present invention is to improve luminous efficiency in a GaN compound semiconductor device having a GaN light emitting layer.

1 is a configuration diagram of an embodiment of the present invention.

FIG. 2 is a manufacturing flowchart of the semiconductor device shown in FIG.

3 is a block diagram of a conventional semiconductor device.

A GaN compound semiconductor device of the present invention includes a substrate, a first conductivity type GaN layer formed on the substrate, a GaN emission layer formed on the first conductivity type GaN layer, and a second formation formed on the GaN emission layer. And a conductive GaN-based layer, a first electrode formed on the first conductive GaN-based layer, and a second electrode formed on the second conductive GaN-based layer. Part of the second electrode is formed of a ZnO transparent electrode. The first conductivity type can be, for example, n-type, and the second conductivity type can be, for example, p-type. ZnO becomes transparent at a predetermined wavelength (350 nm) or more, and can be emitted outside without blocking light from the GaN-based light emitting layer. In addition, the resistivity of ZnO is smaller than that of the metal film and excellent in ohmic contact with the GaN-based layer, so that it is easy to flow a current uniformly into the light emitting layer.

In an embodiment of the present invention, an n-type GaN-based layer, a GaN-based light emitting layer, and a p-type GaN-based layer are sequentially formed on the substrate. A p-type electrode is formed on the p-type GaN-based layer, and a portion of the n-type GaN-based layer is exposed to form an n-type electrode. A ZnO transparent electrode is formed adjacent to the p-type electrode on the p-type GaN-based layer. By making a ZnO transparent electrode and a p-type electrode the same as p-type, electroconductivity improves.

The invention is more clearly understood by reference to the following examples. EMBODIMENT OF THE INVENTION Hereinafter, embodiment of this invention is described based on drawing.

1, the structure of the GaN type semiconductor device which concerns on this embodiment is shown. Although the configuration is almost the same as that shown in FIG. 3, it is different from FIG. 3, and the p-type electrode 22 is formed on the p-type GaN layer 18, and the transparent electrode 21 is formed adjacent to the p-type electrode. . As the electrode, the p-type electrode 22 and the transparent electrode 21 are integrated. This transparent electrode 21 is made of ZnO.

FIG. 2 shows a manufacturing flowchart of the semiconductor device shown in FIG. 1. First, an n-type GaN buffer layer 12 is formed on the sapphire substrate 10 by MOCVD or the like (S101). Preferably, the GaN buffer layer 12 is formed at a relatively low temperature, and prior to forming the GaN buffer layer 12, SiN is first formed, and the GaN buffer layer 12 is preferably formed on the SiN. Next, an n-type GaN layer 14 is formed on the GaN buffer layer 12 by MOCVD (S102). The n-type GaN layer 14 may also be doped with silicon or the like during its formation. For example, the n-type GaN buffer layer 12 may be formed to have a thickness of about 3 μm and the n-type GaN layer 14 may be about 0.1 μm. After the n-type GaN layer 14 is formed, the n-type InGaN light emitting layer 16 is formed, for example, by about 2 nm by the MOCVD method (S103). After the light emitting layer is formed, a p-type GaN layer 18 is formed on the light emitting layer 16 by MOCVD (S104). The p-type GaN layer can be formed, for example, about 0.1 m. After the p-type GaN layer 18 is formed, part of the surface is etched to a depth of about 0.2 µm to expose the surface of the n-type GaN buffer layer 12 (S105). On the exposed n-type GaN buffer layer 12, an Al electrode is formed as an n-type electrode by vapor deposition, sputtering, or the like (S106). Further, a Pt / Au electrode 22 is formed on the p-type GaN layer 18 by vapor deposition or sputtering (S107).

As described above, after the p-type electrode 22 and the n-type electrode 20 are formed, the p-type ZnO transparent electrode 21 is further contacted with the p-type electrode 22 on the p-type GaN layer 18. ) Is formed using a sputtering method or the like (S108). It is known that ZnO becomes transparent at a wavelength of 350 nm or more and can form a film of about 10 ⁻³ Ωcm by sputtering (K. Tominaga, et al, Thin Solid Films 253 (1994) 9-13). ZnO and GaN are lattice constants (ZnO: a = 3.252Å, c = 5.213Å, GaN: a = 3.189Å, c = 5.185Å, ITO: 10.13Å), and coefficient of thermal expansion (ZnO: axial direction 2.9 × 10 ^-6 K ^-1 , C-axis direction 4.75 × 10 ^-6 K ^-1 , GaN: a-axis direction 5.59 × 10 ^-6 K ^-1 , C-axis direction 3.17 × 10 ^-6 K ^-1 ) It is excellent in adhesiveness with the p-type GaN layer 18 and also excellent in etching characteristics. It is also known to form a p-type ZnO film (Jpn. J. AppL. Phys. Vol. 38 (1999) L1205-L1207 Part 2, No. 11A. 1 November 1999), and the p-type GaN layer 18 Electrical contact with can also be made favorable.

Thus, by forming the transparent electrode 21 as ZnO, in particular, p-type ZnO, without forming a transparent electrode as Ni / Au or ITO, the electrical compatibility with the p-type GaN layer 18 is improved and uniform. An electric current can be obtained, and also an electrode shape can be made into a desired shape, and light can be emitted efficiently.

Applicant formed a light emitting device using Ni / Au, ITO, n-type ZnO, and p-type ZnO as a material of the transparent electrode 21, and measured the light emission output. As a result, the following values were obtained. .

Table 1

Transparent electrode material Thickness (micron) Relative output power (20 mA) Ni / AuITOn-ZnOp-ZnO 0.02 / 0.020.20.20.2 10.8-1.21.5-1.81.8-2.0

In the above, the light emission wavelength is all 450 nm. As can be seen from this table, relative to the transparent electrode material (Ni / Au or ITO), both the n-type ZnO and the p-type ZnO have excellent relative output power, and in particular, about p-type ZnO is about twice as much as the conventional one. The relative output power of can be obtained, so that light can be efficiently coagulated and diverted to the outside.

InGaN is used as the light emitting layer in the present embodiment, any material can be used as long as it is a GaN compound semiconductor.

In addition, in this embodiment, although it is a structure of a board | substrate / n-GaN layer / GaN light emitting layer / p-GaN layer, the structure of a board | substrate / p-GaN layer / GaN light emitting layer / n-GaN layer is also possible. In this case, an n-type electrode is formed on the n-GaN layer, and an n-type ZnO transparent electrode is formed adjacent to the n-type electrode.

As described above, according to the present invention, by using ZnO as the transparent electrode, it is possible to efficiently emit light emitted from the light emitting layer to the outside. When such a method is applied to a light emitting element, it becomes possible to improve luminous efficiency.

Claims (4)

Substrate, A first conductivity type GaN layer formed on the substrate, A GaN-based light emitting layer formed on the first conductivity type GaN-based layer, A second conductivity type GaN layer formed on the GaN light emitting layer, A first electrode formed on the first conductivity type GaN-based layer, A second electrode formed on the second conductivity type GaN-based layer, A part of the second electrode is a gallium nitride compound semiconductor device formed of a ZnO transparent electrode. The method of claim 1, The ZnO electrode is a gallium nitride compound semiconductor device of the second conductivity type. Substrate, An n-type GaN-based layer formed on the substrate, A GaN-based light emitting layer formed on the n-type GaN-based layer, A p-type GaN-based layer formed on the GaN-based light emitting layer, An n-type electrode formed on the n-type GaN-based layer, A p-type electrode formed on the p-type GaN-based layer, And a ZnO transparent electrode formed on the p-type GaN-based layer adjacent to the p-type electrode. The method of claim 3, The ZnO transparent electrode is a p-type gallium nitride compound semiconductor device.