JPS5846875B2 - optical semiconductor device - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to an optical semiconductor device using a compound semiconductor,
In particular, the present invention relates to a light-emitting element that emits green or blue light with high efficiency and an element that selectively and efficiently receives high-energy light.

Currently commercially available green light-emitting devices generally use GaP, which is a ■-V group compound semiconductor.

However, GaP green light-emitting devices emit light in yellow-green (wavelength 560 to 570 nm) rather than completely green, and the brightness is only about 100% lower than that of red light-emitting devices, which are major factors preventing the market from expanding. It becomes.

On the other hand, the development of green or blue light-emitting devices using semiconductors with a wide forbidden band width such as GaN*Zn5jZnSe is being actively pursued, but all of these materials exhibit only n-type conduction and cannot form good p-n junctions. Because, M.I.S.
``Elements with a (metal-insulator-semiconductor) structure have only been prototyped, but their luminous efficiency is low and there is no prospect of practical application yet.

In addition, existing semiconductor photodetectors have a small forbidden band width, so
Green: Low sensitivity to high energy light such as blue.

The first object of this invention is to provide a compound semiconductor light emitting device that emits green or blue light with high efficiency.
The gist is n-type ZnS, which has a wide forbidden band width, and p-type CuGaS2h, which is a chalcopyrite compound semiconductor, and GaAA! The purpose is to use a heterojunction with a mixed crystal consisting of S2.

A second object of the present invention is to provide a highly sensitive element that selectively receives high energy light through the heterojunction.

Since ZnS has a large forbidden band width of 3.6 eV and a direct transition type band structure, it has attracted attention as a green or blue light emitting material, but as mentioned above, ZnS has a good pn
Since no bonding is possible, the injection efficiency is low, and only MIS structures have been prototyped in the past.

On the other hand, I-II[-
The forbidden band width of V12 group compound semiconductors varies greatly depending on the constituent elements, and because they have a direct transition type band structure like the ■-■ group compound semiconductors, they have been viewed as promising materials for light-emitting devices.

Therefore, the present inventors found that the bunt structure 5 of the I-TII-VI group 2 compound semiconductor is similar to that of the [-VI group compound semiconductor, that there is not much difference ξ in the lattice constants of the two, and that
-III-V In consideration of the fact that n-type conduction can be obtained in the 12-group semiconductor, an n-type ■-■ group compound semiconductor and a chalcopyrite-type p-type I-m-V 12 group compound semiconductor are combined. An attempt was made to form a telojunction.

As a result, CuGaS2 and C
When a mixed crystal of uAAS2, that is, CuGa1-xAAxs2, was grown, a good heterojunction with little lattice mismatch could be formed, and by changing the mixed crystal ratio This makes it possible to realize a highly efficient light-emitting element that changes.

By the way, CuGaS2 has a forbidden band width of 2.44 eV.

Lattice constant 5.35A, forbidden band width 8.35 for CuAAS2
eV, and the lattice constant is 5.33A, and the lattice constants of both are almost the same. Therefore, the forbidden band width can be set to 2.44e without disturbing the crystallinity due to the mixed crystal of CuGaS2 and CuAlS2.
It can be changed from V to 8.35eV, green,
It can be seen that it is suitable as a blue and violet luminescent material.

In fact, the ZnS crystal that becomes the substrate is CuGaS2*- and C
The lattice constant is very close to uAAS2, so n-type ZnS
A good heterojunction can be formed at the interface between CuGa1-xAlX52 and CuGa1-xAlX52.

Furthermore, since the forbidden band width of ZnS is 3.6 eV, which is wider than that of the above-mentioned mixed crystal, light emission occurs on the mixed crystal side. Therefore, by changing the mixed crystal ratio, the emission wavelength changes significantly, and a green to violet light emitting element is produced. is obtained.

On the other hand, the above-mentioned heterojunction has unique characteristics as a light-receiving element, and by changing the mixed crystal ratio of CuGa1-xAAxs2, the wavelength of effectively absorbed light changes. Light can be selectively received.

In addition, ZnS crystal has a wide forbidden band width of 3.6 eV, so it is transparent to green, blue, etc. light, and if light is incident from a ZnS crystal measurement, the incident light will effectively reach the p-n junction. This results in an element with high light-receiving sensitivity.

Examples will be described below with reference to the drawings.

Example 1 An Al-doped ZnS single crystal grown by high-pressure melting was heat-treated in zinc to form a low-resistance n-type crystal, and a wafer with a (100) main surface was formed.

Then, as shown in FIG. 1, this n-type ZnS wafer 1
A p-type CuGa, -xAlxs2 layer 12 was grown on the substrate 1 by liquid phase epitaxial (LPE) growth to form a pn junction 13.

For LPE growth, a Ga melt was used as a solution, and a small amount of AA added to a synthesized CuGaS2 polycrystal was used as a source.

The growth temperature was 1000° C., a 1 mm thick Ga melt was poured between the source crystal and the wafer, and isothermal growth was performed with a temperature gradient of 10° C./crrL.

This results in a homogeneous CuGa1-XAl with a thickness of approximately 20 μm.
An X52 layer was obtained.

The amount of 1 added was approximately 2 mol, and the mixed crystal ratio of the grown layer was x = 0.22.

Since the growth was performed at an isothermal temperature, there was little change in the mixed crystal ratio X in the growth direction, and the pn junction surface was also good.

The epitaxial layer that forms a heterojunction in this way
The wafer was cut into Q, 5 mm square chips, and as shown in Fig. 2, ohmic electrodes 14 and 15 containing In as a main component were attached to the nfjlLp electrodes, respectively, and the chips were placed on the ladder 16 to the To-18 with the p side on top. The electrode 15 of p([0) was connected to the terminal 17 by bonding, and finally an epoxy resin 18 was molded.

Terminal 17.19 of the light emitting diode made in this way
When a forward current of 20 mA is passed between the two, the emission wavelength is approximately 500 nm.
It exhibited clear green light emission, and its luminous efficiency was about 0.2%.

This is the efficiency of the conventional GaP green light emitting device of 0.05 to 0.
This is very high compared to 1 sin.

Example 2 Three types of epitaxial growth were performed in the same manner as in Example-1 except that the amount of AA added was changed, and diodes were formed for each, and the emission wavelength and luminous efficiency were measured.

The results are shown in FIG. 3 and FIG. 4 together with the case of Example-1.

By increasing the amount of A[ added, the mixed crystal ratio X increased significantly, and accordingly, the emission wavelength shifted to the shorter wavelength side, making it possible to obtain light emission from green to blue.

Note that, as mentioned above, the forbidden band width (2,44 to 3.35 eV) of CuGa1-xAlx52 is smaller than that of ZnS (3,6 eV), so CuGa, -x
It is desirable to emit light on the AlxS2 layer side, and therefore, to increase the luminous efficiency, use a high quality p-type CuGa1xAlxS2 layer.
The important point is to grow the layers.

It is the conclusion of the present inventors that the LPE growth method is suitable for this purpose.

In order to perform LPE growth on the CuGaS2 layer, a thin solution should be used to prevent non-uniform growth within one plane. (2) In order to reduce the change in composition in the growth direction, especially the change in the mixed crystal ratio X. (3) Since S has a high vapor pressure, a polycrystalline CuGaS2 source should be used; (4) The growth solution should be made of Ga, which is a constituent element of the growth layer, in order to prevent impurity contamination. The important point is to use a melt.

[Brief Description of the Drawings] Fig. 1 is a diagram showing an epitaxial wafer prepared in an embodiment of the present invention, and Fig. 2 is a structure of a light-emitting device made by cutting out a chip from the wafer and mounting it on a header. Figures 3A and 4 are diagrams showing data obtained by measuring the luminous intensity and luminous efficiency of light emitting devices obtained by changing the mixed crystal ratio X of the epitaxially grown layer. 11... n-type ZnS woo-11-ha 12. p-type Cu
Ga1-XAlX52 layer, 13... pn junction, 14.
15--ohmic electrode, 16--To-18 header, 17°19-- terminal, 18-- epoxy resin.

Claims (1)

[Claims] 1 n-type ZnS and p-type CuGa1-xAA? An optical semiconductor device characterized by having a heterojunction with xS2.