JPS6092609A - Liquid-phase epitaxial growth method - Google Patents

Abstract

PURPOSE:To form an approximately flat and uniform P-N junction by making a point of time when the speed of temperature drop is changed over and a point of time when a melting liquid is changed over differ after the first epitaxial growth of a compound semiconductor for a light-emitting diode. CONSTITUTION:A P type GaAs substrate 1, a P type melting liquid and an N type melting liquid are kept at 850-900 deg.C, the substrate and the P type melting liquid are brought into contact and the temperature of the substrate is elevated at a point of time t1, the temperature of the substrate is lowered at the first speed of temperature drop at a point of time t2 when the temperature of the substrate reaches to 860-950 deg.C, the first epitaxial growth is executed, thus forming a P type GaAlAs layer 2. The temperature of the substrate is lowered at the second speed of temperature drop at a point of time t3 when the temperature of the substrate lowers to 820-900 deg.C, the melting liquid is changed over to the N type melting liquid at a point of time t4 when the temperature of the substrate drops by 5-13 deg.C, and the second epitaxial growth is executed, thus forming an N type GaAlAs layer 3. Silicon as a very small amount of an impurity displays determined conduction action of either of a doner or an acceptor, and is not inverted into a P type or an N type in the vicinity of a P-N junction 4.

Description

DETAILED DESCRIPTION OF THE INVENTION A) Field of Industrial Application The present invention relates to a liquid phase epitaxial growth method for producing a light emitting diode using a Pr+ junction with good characteristics.

(2) Prior art In recent years, C5 has become the first compound semiconductor for light-emitting diodes.
As shown in the figure, GaAs of the same conductivity type is placed on the GaAs substrate (1).
An AlAs layer (2) is grown, and then GaA of the opposite conductivity type is grown.
A technique has been developed to increase the injection efficiency near the Pn junction (4) by stacking lAs layers (3).

Perfect for liquid phase for light emitting diodes like this! As shown in the temperature characteristic diagram of Fig.
At time t3, the melt is brought into contact with the substrate, and the first epitaxial growth is performed between t2 and t3. 2 epitaxial growth was being carried out.

In this method, a Pn junction (4) is formed at time t3, but a planar Pn junction cannot be obtained even though the wafer is in surface contact with the melt. In other words, the conductivity type may be partially changed quickly, or the conductivity type may be changed many times and P
When forming an nPn structure, the 11(min) may be reduced by 1/1.These are not preferred because they not only reduce the luminous efficiency but also cause a switching operation like a transistor or thyristor. , I don't know.

As a result of repeated experiments, we found that a small amount of silicon contained in the melt acts as an amphoteric impurity for GaAs and GaAlAs, and that the temperature decreases during epitaxial growth.
It determines whether it will become a type impurity or an n-type impurity, so if the melt and temperature gradient are changed at the same time, it will partially become a p-type or an n-type due to thermal inertia, etc., so this may be the cause. I understand. On the other hand, constant temperature maintenance and meltback near the Pn junction, which are used in liquid phase epitaxial growth methods for other compound semiconductors, are difficult because the mixed crystal ratio of the ternary compound changes before and after the Pn junction (4). It has been found that this is undesirable because there is a risk that the mixed crystal ratio may deviate from the optimal value for light emission, and in particular, the efficiency of current injection into the P layer, which is the light emitting layer, tends to decrease.

C) Purpose of the Invention The present invention has been made in consideration of the points mentioned in E above, and provides a liquid phase one-pitaxy growth method for forming a substantially flat and uniform Pn junction.

2) Structure of the invention The present invention provides that after the first epitaxial growth of a compound semiconductor,
The present invention will be described in detail below based on examples.

e) Example FIG. 3 is a temperature characteristic diagram of the liquid phase shrimp/kill growth method according to the example of the present invention. The following explanation is based on G explained in Figure 1.
A GaAlAs light-emitting diode on an aAs substrate will be taken as an example, and the atmospheric gas will be hydrogen unless otherwise noted.

First, a P-type GaAs substrate, P-type melt, and N-type melt were separated and set in a graphite boat at 850 to 900°C.
At time t1 in FIG. 3, the slide plate of the boat is slid to bring the substrate into contact with the P-type melt. Then, the temperature is raised rapidly to improve the wettability of the substrate surface and to cause a slight elution (melt back), and when the temperature reaches 860 to 950°C, t2i is heated to, i to o, s°C/ The temperature is lowered at the first cooling rate of min, and the first Ebidaki/Yal growth is performed to form P-type G.
aAlAs layer is formed. Sled, T: 820-90
At t3, when the temperature was lowered to 0℃, the temperature decrease rate was increased to 2 to 5℃/
5 to 1 from the temperature at that time.
At time t4 when the temperature has decreased by 3° C., the melt is switched from the P-type melt to the N-type melt. After that, if necessary, add 1 to improve the ohmic characteristics of the electrode, and use the final 10°C temperature drop to improve the ohmic characteristics of the electrode.
A surface layer (5) may also be formed.

The growth layers and Pn junctions grown in this way have high luminous efficiency because the crystallinity of each layer is well matched, and silicon, which is a trace impurity, exhibits a conductive function as either a donor or an acceptor, and the Pn junction It does not become P type or invert to N type in the vicinity of the junction.

In the above-mentioned GaAlA3 light emitting diode manufactured by this method, for example, no etching line due to poor crystalline matching was observed between the substrate and the first epitaxial layer, and the P-type Ga1-8AlxAs layer near the Pn junction was not observed. The mixed crystal ratio X was approximately 0.35, the luminous efficiency after coating with 1 boxy resin was 4 to 5%, and the luminescent wavelength was 66 (1++ m (red)).

f) Effects of the Invention As described above, the present invention maintains a plurality of melts and a compound semiconductor substrate at a high temperature, brings the first melts into contact with the substrate, and conducts a first epitaxy process at a first cooling rate. The process of growing;
Since it is a liquid phase epitaxial growth method that includes a step of changing the temperature to a second cooling rate, and then a step of bringing the second melt into contact with the substrate and performing second epitaxial growth at the second cooling rate, it has good characteristics. A Pn junction can be formed.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of a compound semiconductor for light emitting diodes which is the subject of the present invention, Fig. 2 is a temperature characteristic diagram of a conventional l-bitaxial growth method, and Fig. 3 is a liquid phase epitaxial growth method of an embodiment of the present invention. FIG. (1)・=GaAs substrate, (2)(3)-Ga^1AJ
t, (4)=-Pn junction, 5)...GaAs surface layer.

Claims (1)

[Claims] l) A plurality of melts and a compound semiconductor substrate are held at high temperatures, and the first melt and the substrate are brought into contact with each other, and a first epitaxy is grown at a first cooling rate. Liquid phase epitaxial growth characterized by a step of bringing a second melt into contact with the substrate and then growing a second epitaxial layer A.1 at a second cooling rate. Way d1. .