JPS5918877B2 - optical semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical semiconductor device using a compound semiconductor heterojunction.

What green light-emitting elements are currently commercially available?

■-GaP, which is a group V compound semiconductor, is commonly used.
and the brightness is about 1
The low value of /3 is a major reason for hindering the expansion of the market. On the other hand, Z
The development of green or blue light-emitting devices using semiconductors with wide forbidden bands such as nS, ZnSe, and CdS is being actively pursued, but these materials exhibit only n-type conduction and do not have good p-type conductivity.
Since n-junctions cannot be formed, devices with an MIS (metal-insulator-semiconductor) structure have only been prototyped, but their luminous efficiency is low and there is no prospect of practical use yet.

This invention is based on ZnS3-x, which is a ■-■ group compound semiconductor.
Sex and chalcopyrite compound semiconductor Cu, -yA
High quality pn in combination with gyGa1-2Al2S2
By forming a junction, it is possible to provide an optical semiconductor element that exhibits highly efficient light-emitting or light-receiving characteristics in a green to violet region.

That is, the optical semiconductor device according to the present invention is made of ZnS3-xSe.
It is equipped with a heterojunction between Depending on the value of the ratio z, Cul-yAgyGa,
-2The band gap of the two Al2S layers is defined.

Chalcopyrite type A ■-■ group compound semiconductor is ■-■
Since it has similar lattice constants and band structures to group compound semiconductors and is p-type, it was fully expected that a high-quality pn junction could be obtained by a heterojunction between them.

Furthermore, since these materials have a wide forbidden band width and a direct transition type band structure, they are considered promising as materials for green to violet light-emitting devices. However, in order to form a high-quality heterojunction, it is extremely important to match the lattice constants of the two as much as possible. Therefore, as a result of repeated experiments, ZnS3
-xSex(5Cu, -yAgyGa0-2Al2S2
In the heterojunction with
Moreover, by changing the mixed crystal ratio z, the peak wavelength of light emission can be changed arbitrarily. This device succeeded in emitting light ranging from green to purple. Furthermore. Cu, -YA with different mixed crystal ratios z
By stacking multiple layers of gyGa,-ZAl2S,
Highly efficient light emission was observed due to the carrier confinement effect. The effects of this invention are explained below based on examples. Clarify the reasons for limiting the mixed crystal ratio.

Example 1 As shown in Fig. 1, a wafer 1 having a (100) main surface was cut out from an n-type ZnS single crystal by high-pressure melting. On this (100) main surface, p-type Cu, -YAgyGa, -2
A1zS2 (y=0.15, z=0.2) layer 2 is grown by liquid phase epitaxial growth from Ga melt 6, and Pn is added at the interface.
Joint 3 was formed.

Liquid phase growth was performed using a slide boat method, and CuGa
s2 polycrystal. Thickness 3jE1f with addition of Ag and A1
) The Ga melt and the wafer were brought into contact at 1000° C., and epitaxial growth was performed with a temperature gradient of 10° C./Cm perpendicular to the wafer. The mixed crystal ratio y<5z is Ga
It is controlled by the amounts of Ag and Al added to the melt. y=
To make it 0.15, the amount of Ag added is 1.5m01%. z
=0.2, the amount of A1 added was 0.5m01%. The obtained p-type CUl-YAgyGa,-ZAl2
The thickness of S2 layer 2 is 30 μm! ). In the growth direction, y and X were almost constant, and the Pn junction surface 3 was also flat.

A 0.5 mu square chip was cut from the epitaxial wafer thus produced. As shown in FIG. 2, ohmic electrodes 4 containing In as a main component on the n side and p side
, 5 was formed and mounted on a TO-18 header 6, and after bonding was made between the electrode 5 and the positive lead terminal 7, it was molded with epoxy resin 8 to form a light emitting diode.

9 is a negative side lead terminal.

When a diode forward current of 20 mA was passed between lead terminals 7 and 9, very bright green light was emitted.

The peak wavelength of light emission was approximately 500 nm, and the light emission efficiency at this time was 0.3%. Compared to the conventional GaP green light emitting diode. Its practical value is great because the luminescent color is pure green and the luminous efficiency is about 5 times higher. Example-2 The amount of Ag added is constant (y=0.15). Example-1 except that the mixed crystal ratio z of the growth layer was changed by changing the amount of A1 added.
A light emitting diode was fabricated using a process similar to the above, and the relationship between the B6 mixed crystal ratio z and the emission wavelength was investigated.

The results are shown in FIG. 3 together with the results of Example-1. As is clear from Fig. 3, the band gap of the grown layer changes by changing the mixed crystal ratio z. It exhibited highly efficient light emission in the green to violet range. The luminous efficiency decreased little by little as z increased, and was 0.1% at z = 0.70. The rate of change in luminous efficiency was gradual. In addition. ZnS
, −XSex (0 x A good quality heterojunction can be obtained if the value of the mixing ratio y is 0.65x + 0.1≦y
This was the case when the range was selected to be ≦0.65x+0.2.

Example 3 In the same manner as in Example 1, n-type Zn was prepared as shown in Figure 6.
CU of 3 layers of VC on S wafer 11, -YAgyGal-,
Z. The Al7, S2 layers 12, 13, and 14 were grown by liquid phase growth.

The first layer 12 is an n-type layer with y=0.15 and z=0.3 and has a thickness of 10 μM.The second layer 13 is a p-type layer with y=0.156 and z=0.1.
The mold layer has a thickness of 1 μM. The third layer 14 is y=0.156z=0
．． The p-type layer No. 3 has a thickness of 10 μm. Note that the first layer 12
To make it n-type, it was necessary to add Zn, Cd, or a halogen substance. When a diode similar to that shown in FIG. 2 was made from the epitaxial wafer obtained in this manner, very high efficiency blue light emission was observed with a light emission wavelength of 510 nm and a light emission efficiency of 0.4%.

The reason why such high efficiency was obtained was that the second active layer
The first layer 12 and the third layer 14 in which the layer 13 has almost the same lattice constant
The lattice mismatch is extremely small because it is sandwiched between the 6th and 1st
A high quality Pn junction is formed between the layer 12. This is also considered to be because the carrier confinement effect is working effectively.
Although the above description has focused on a light-emitting device, the heterojunction device according to the present invention is also useful as a light-receiving device that selectively receives light in the green to violet region.

[Brief explanation of the drawing]

FIG. 1 shows an epitaxial diagram in one embodiment of the present invention.
FIG. 6 shows the cross-sectional structure of the wafer. FIG. 2 shows the cross-sectional structure of a light-emitting diode made by cutting chips from the wafer. FIG.
．． Z. Figure 6 shows the measured data of the change in emission wavelength when the mixed crystal ratio Z of the Al2S2 layer is changed. Figure 4 is a cross section of an epitaxial wafer in another example in which a Pn junction is created in the growth layer. It is a figure showing a structure. 1... N-type ZnS wafer 2... P-type Cu, -YAgyGa, -ZAlzS 2 layers, 3...
...Pn junction 64,5...Ohmic electrode 66
...TO-18 header, 7,9...Lead terminal 68...Epoxy resin, 11...
・・n-type ZnS Waeno＼ 12・・・・・・n-type Cu,
-YAgyGa, -7. AlzS2 layer (y=0.15,
Z. =0.3). 13...p-type Cu, -YAg
yGa, -2A17. s2 layer (y=0.15, z=0.
1). 14...p-type CUl-YAgyGal-
7. Al2S2 layer (y=0.15, z=0.3).

Claims (1)

[Claims] 1 ZnS_1_-_xSe_x and Cu_1_-_yA
It has a heterojunction with g_yGa_1_-_zAl_zS_2, and the mixed crystal ratios x and y are 0≦x≦1 and 0.
65x+0.1≦y≦0.65x+0.2, and depending on the value of the mixed crystal ratio z, the Cu_1_-_yAg_yG
A semiconductor device characterized in that a band gap of a_1___zAl_zS_2 layer is defined.