JPS58196013A - Method for liquid phase epitaxial growth - Google Patents

Abstract

PURPOSE:To provide epitaxial growth crystal with little crystal defect, by a method wherein GaAs crystal for preventing supersaturation of As in solution during cooling the solution is contacted to active layer entered in a solution vessel and upper portion of solution for cap layer. CONSTITUTION:Specified amount of solute of Al, n type impurity Te, p type impurity Zn is solved uniformly, and Ga solution to solve As in saturation is prepared at solution vessels 6-9 within H2 vapor of 760 deg.C. Solutions for various layers are entered in growing solution vessels 15-18 through small holes 11-14 provided on a boat part 10. GaAs crystals 19, 20 for preventing supersaturation of As in the solution during cooling are contracted to active layer entered in the vessels 16, 18 and upper portion of solution for cap layer. Temperature of the system is decreased and the solution is transferred, and solution for n-clad in sequence from the vessel 15 is contacted to a substrate crystal 21 thereby epitaxial multi-layer growth is performed at prescribed thickness and composition.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a liquid phase epitaxial method for the purpose of manufacturing compound semiconductor laser devices, and in particular to a method for crystal growth suitable for reducing crystal defects that cause poor injection current-optical output characteristics of the device. Regarding the method.

A liquid phase epitaxial method using a slide boat is widely used as a method for continuously growing multiple layers of AlxAs for the purpose of manufacturing semiconductor laser devices. A growth Ga solution in which a predetermined solute is uniformly dissolved at a predetermined temperature and is saturated with Asi is passed through small holes for the purpose of removing At, O, and slag generated in the solution.

Thereafter, the solution is successively brought into contact with the substrate crystal while lowering the temperature of the reaction system to complete the desired multilayer growth. In the conventional method described above, each growth solution is supercooled before it contacts the substrate crystal due to a drop in temperature. In order to bring the solution into contact with the substrate crystal and cause epitaxial growth, the solution housing t is moved from the n-th point from the gap provided between the substrate crystal surface and the bottom of the boat part having the solution reservoir when moving the substrate crystal. A part of the solution is mixed into the (n+1)th solution.

If the At content in the (n+1)th solution is smaller than that in the nth solution, the solubility of As in the (n+1)th solution decreases due to the mixing of the nth solution,
There was a drawback that KGaAtAs microcrystals were formed in the solution, and the microcrystals adhered to the surface of the epitaxially grown crystal, causing defects that adversely affected device characteristics.

An object of the present invention is to provide an epitaxially grown crystal t* with fewer crystal defects that adversely affect the characteristics of a semiconductor laser device.

From Figure 1, G1. It can be seen that the higher the At content in the solution, the lower the solubility of As in the Ga solution in which , xAlxAs is grown. Therefore, in a supercooled growth solution immediately before epitaxial growth in contact with a substrate crystal, Att which has a higher Aj content than the solution.
If a solution having a certain amount of Aa is mixed in, the degree of supersaturation of Aa in the former solution will increase, and GaAlAs microcrystals will crystallize in the solution. The core microcrystal is deposited on the surface of the epitaxially grown crystal, but stochastically, the crystallographic orientation of the microcrystal is relatively different from that of the epitaxially grown crystal. In the direction of growth
This causes defects that become concave holes that reach the surface of the final multilayer epitaxial layer. This crystal defect appears as a cause of the characteristics of a semiconductor laser device, especially a non-oscillating device. As a method for preventing the generation of crystal defects, a QaAs crystal is brought into contact with a solution having a relatively low At content, and the degree of supersaturation of As in the solution accompanying the temperature drop in the reaction system is alleviated. A method was used to control the amount of dissolved As at the solution temperature so that the amount of dissolved As was near the equilibrium concentration.

An embodiment of the present invention will be described below. FIG. 2 shows the structure of the visible semiconductor laser device manufactured. In Fig. 1, 1 is an n-QaAs substrate, 2 is an n-Gan, ss A
41. 41 people in 1st layer, 3 in GA6. B A 16.4
A 8 layers (active layer), 4 is P-G”o, *s
A to, 4@As layer, 5 is an n-GaA1 cap layer. In liquid phase epitaxial growth to realize this device, the solution for the active layer 3 and the cap layer 5 is
The t content is designed to be smaller than the At content in the solutions for the n-cladding layer 2 and the p-cladding layer 4, which are the previous solutions. Therefore, n-cladding layer 2
In order to prevent the crystallization of GaAtAs microcrystals into the active layer and cap layer solutions due to the mixing of the solution for the active layer 3 into the solution for the active layer 3 and the mixing of the solution for the p-cladding layer 4 into the solution for the cap layer 5, Growth was carried out with a KQaAs crystal in contact with the layer and cap layer solutions as shown in FIG.

The details of the growth are as follows. First, solutes of Atgn type impurity Te and P type impurity Zn are uniformly dissolved in predetermined amounts,
Qa bath solution that saturates As, solution reservoirs 6, 7, 8.9
After that, the small holes 11, 12, 13, 14 provided in the boat part 10
The solutions for each layer are passed through the growth solution reservoirs 15, 16, 17.
．． I put it in at 18. At this time, Qjl and l1k11 for the purpose of preventing supersaturation of As in the solution as the solution cools are placed above the active layer and cap layer solutions entering the solution reservoir 16.18.
Crystal 19,201-contacted. Next, 0.
While lowering the temperature of the system by 5tZ'/-, at a point when the degree of supercooling of the solution reaches 5C, the solution is moved and sequentially contacts the substrate crystal 21 starting from the n-cladding solution 1 in the solution reservoir 15. Then, epitaxial multilayer growth with a predetermined thickness and composition was performed. In the case of the conventional method in which the aAs crystal is not brought into contact with the solution for the active layer and the cap layer, defects caused by GaAtAs microcrystals crystallized in the solution are generated in the growth wafer 7.
The defect density was 5,000 to 12,000 defects/cm" per surface, but with the method of this example, the defect density was reduced to 30 to 10
00 care cm''. Furthermore, when semiconductor laser devices were fabricated from growth wafers fabricated by the conventional method, the incidence of non-oscillating devices was 15 to 35%. The incidence of non-oscillating elements was 0 to 5%.

According to the present invention, excessive supercooling of the growth solution can be prevented;
Since defects based on this can be reduced, there is an effect of improving the characteristic yield of semiconductor laser devices.

[Brief explanation of the drawing]

FIG. 3 is a side view of the graphite boat as seen from the end face direction of the element.

Claims (1)

[Claims] 1. GJIm, z kl by slide-boat system
, xAs (Ox<;:1) In continuous multilayer liquid phase epitaxial growth, a predetermined solute is uniformly dissolved in a solution reservoir provided for the purpose of separating each required solution,
And when used as a Ga solution saturated with As, At
When a layer (X,) with a relatively large mixed crystal ratio X is grown next to a layer (X,) with a relatively small X (Xs < Xs), supersaturation of As in the iron solution occurs only in the latter solution. A liquid phase epitaxial growth method characterized by keeping GJIAI crystals in contact with each other for the purpose of lowering the temperature.