JPH01179792A - GaAlAs liquid phase crystal growth method - Google Patents

Abstract

PURPOSE:To easily obtain a Ga1-xAlxAs crystal having a desired compsn. when a Ga1-xAlxAs crystal is grown in a liq. phase by a temp. difference method by deciding the growth temp. of the crystal by a specified relational equation. CONSTITUTION:When a Ga-Al-As crystal is grown in a liq. phase by a temp. difference method by which a temp. difference is produced in a melt prepd. by dissolving Al and Ga-As in Ga as a solvent and a substrate is brought into contact with the low temp. part of the melt to grow the Ga-Al-As crystal, the growth temp. T( deg.C) of the crystal is decided in accordance with the desired compsn. (x) of the Ga1-xAlxAs crystal by an equation T=alpha.x-beta+ or -10% (alpha=291.5 and beta=793.0), the melt is prepd. and the crystal is grown.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention relates to the crystal growth of GaAl^S, in particular, by providing a certain temperature difference in a melt containing a solute and continuously growing the crystal from a high temperature region to a low temperature region. This invention relates to liquid phase epitaxial crystal growth of GaAlAs by a temperature difference method in which a solute is transported to grow a crystal in a low temperature region.

[Prior art] The bandgap energy of G a 1- x A l x A S can be changed from 1.43 eV to 2.16 eV by changing the composition x (proportion of At^S) in the crystal. It is a mixed crystal semiconductor. Therefore, Ga1
-xAlxAs is widely used as a material for light emitting diodes (LEDs) ranging from infrared light to visible light.1 For example,
To obtain a red LED with a wavelength of 660 nn, the p-
Ga, -xAtxAs is approximately 0.35. wavelength 780
Nike X to get nl LED about 0.15. wavelength 850
To obtain an nn+ infrared LED, X should be approximately 0.01, therefore.

In a GaAlAs LED, X of p-Ga ^l As is determined depending on the target emission wavelength. X in n-Ga1-1-xxxAlxAS is also not constant and is determined depending on the target emission wavelength. n-Ga1. X of AtxAs is used to confine electrons and holes in the p-Ga1-xAlxAs light-emitting layer, or for p-Ga1. ^1xA
A value is selected that is necessary to effectively guide light emitted from the s-layer to the outside of the crystal without absorbing it. For example, p-Ga1-x^lx
When X of As is 0.35, n-Ga1. AlxA
X of s is chosen to be 0.6-0.85.

The active region of an LED is usually made by epitaxial growth on a substrate crystal. As the substrate crystal, it is desirable to obtain one that is not expensive, has a large diameter, and has good crystallinity.The Ga, ..., AlxAs mixed crystal has a small lattice mismatch with the GaAs crystal over the entire range of composition X. Therefore, It is possible to epitaxially grow high-quality Ga1-xA1xAS on a GaAs substrate from which a large-diameter, high-quality crystal can be obtained. For these reasons, GaA IAs are currently widely used as high-brightness, high-output light emitting diodes that emit light from infrared light to red light.

When using Ga1-xAlxAs as such a light emitting device, the composition X
Controlling this is an important issue.

The slow cooling method, which is known as a liquid phase crystal growth method such as the slow cooling method and the temperature difference method, is a method in which a melt is gradually cooled and crystallized.

The temperature difference method is a method in which a high temperature part and a low temperature part are formed with a certain temperature difference (or temperature gradient), and raw materials are supplied from the high temperature part and crystals are precipitated in the low temperature part. Temperature difference method liquid phase crystal growth refers to a method in which the solute is dissolved (supplied) in a high temperature section, transported to a low temperature section by temperature gradient and diffusion, and then precipitated from a supersaturated solution in the low temperature section. Because growth is performed at a constant temperature rather than gradually lowering the temperature as in the slow cooling method, there are fewer crystal defects and fluctuations in crystal composition and impurity concentration due to temperature changes, and large numbers of sheets can be grown continuously. GaAlA
In the case of s-based crystals, Ga is placed in a melt bath made of graphite.
By this method, a melt consisting of a solution is introduced and crystal growth is performed at 800°C to 1000°C, preferably 850°C to 950°C, with a temperature difference of 10°C to 60°C. is being produced.

[Problems to be Solved by the Invention] When a mixed crystal is precipitated from a melt, the composition of the solute in the melt and the composition X of the growing crystal are generally not equal and vary depending on the growth temperature.

However, in the temperature difference method crystal growth of Ga1-x^lx As, no clear relationship has been found between the growth temperature and the crystal composition X, and in order to obtain the desired composition The experiment had to be repeated.

The object of the present invention is to obtain Ga1-xAtxAs of a desired composition.
An object of the present invention is to provide a method for growing AlxAs crystals.

[Studies carried out to solve the problem] Generally, the composition X of Ga1-X A18^S crystal grown by liquid phase growth is determined by the concentration of A1 in the solution (melt). In the slow cooling method that is widely used as a liquid phase epitaxial growth method, for example, 1) 19685YHPO8I
UHon GaAs, paper 12) Jall,
J, At)l)1. Phys, Vol. 18. no,
8, 1979.1) 1509, the concentration of A1 in the solution and the growing Ga1. It is known that a certain relationship exists between the composition X of the AlxAs crystal. This relationship is reproduced in FIGS. 3 and 4. Using these, the amounts of A1 and GaAS, which are materials, and Ga, which is a solvent, can be easily determined according to the composition X of the growing Ga1-x^IxAs crystal and the growth temperature. The desired Ga1. Using the composition X of the AlxAs crystal and the growth temperature which is the temperature of the melt low temperature part or the substrate, the third
From the figure, the weight ratio of A1 in the solvent Ga [Al1 /[
Ga] is obtained. From FIG. 4, which shows the saturation solubility of GaAs in an Al-Ga solution using this IAl]/[Ga] and growth temperature, the amount of dissolved GaAs is expressed as the weight ratio of GaAS to the solvent Ga, [GaAs]/[Ga]. Desired. This [Al1/[Ga] and [GaAs
] / [Ga] to form a growth melt by weighing the amount of each material.

However, in the temperature difference liquid phase epitaxial growth method, the relationship between
5 The present inventors conducted many more experiments and found that in the temperature difference method liquid phase epitaxial growth method, there is a certain relationship different from that in the slow cooling method. By utilizing this relationship, Ga1.
It proves very useful when growing AlxAs crystals.

[Means for solving the problem] In the temperature difference method liquid phase crystal growth of Ga1-xAlxAS, the relationship shown in Fig. 1 holds true, and the weight ratio of Al and GaAs dissolved in the melt [Al]/ [GaAs
]□If y is constant, the growth temperature T is 1 Ga7.
It has a relationship expressed by a certain formula with the composition X of the AtX^S crystal.

Namely.

T = α・X + β ± 10% (1) α=29
1.5, T may be determined according to β=793.0.

[Function] Ga1. by temperature difference method. It was discovered in the liquid phase crystal growth of AtxAs. Since the growth temperature is determined using natural laws different from the slow cooling method, Ga1 with the desired composition
．． An epitaxial layer of AlxAs can be grown.

[Example] FIG. 5 schematically shows an example of a temperature difference method liquid phase growth apparatus. A control device 50 has a built-in computer and can control the entire growth apparatus. A slider 53 on which a semiconductor substrate is placed is housed in the entrance side preliminary chamber 51, and the slider 53 is pushed up.
The treetops are then forced up through the gate valve 62. Preferably, the entrance side preliminary chamber 51 is preheated in a preliminary heating furnace 59. The pushed-up slider is sent into the growth chamber 57 through a gate valve 63 by a slider drive mechanism 61. A melt tank 64 is provided in the growth chamber 57, and the main heater 67 heats the melt tank 64. The substrate 69 on the slider 53 comes into contact with the melt at the bottom of the melt tank 64 to perform crystal growth.The slider carrying the substrate on which the crystal growth has been completed is sent out of the growth chamber 57 via the gate valve 73, and the slider receiving mechanism Gate valve 74 by 77
It is stored in the outlet side preliminary chamber 79 via the. Each drive mechanism 5
5, 61, 77, heater 59, 67, etc. can be controlled by the control device 50. The control device 50 further stores equation (1) and its modified form.

If necessary, it is possible to calculate each parameter, display instructions to the operator based on the results, perform automatic control, etc.

FIG. 6 is an enlarged explanatory view of one example of the melt tank 64 portion.

Solutes Al and GaAs are dissolved in Ga, which is a melt, and stored in a p-melt tank 65 and an n-melt tank 66. Further, as impurities, 2n is dissolved in the p-melt tank 65 and Te is dissolved in the n-melt tank 66. In order to make the band gap of the n-type region that will be grown later larger than that of the p-type region, it is preferable that the amount of A1 in the n-melt tank 66 be larger than the amount of A1 in the p-melt tank 651. To obtain a Ga1-xAtxAs light emitting diode, one composition X should be approximately 0.35% in the p-type region. A vertical temperature difference as shown on the right side of the figure is set in the single melt tank 65° 66 in which the amounts of A1 and GaAS are determined to be about 0.6-0.85 in the n-type region. For example, 850℃
A temperature difference of 10°C-60°C is provided at a temperature of -950°C. To continuously supply the solute, the solute may be floated on the top of the melt, which is the high temperature section, or a solute containing section may be created and brought into contact with the melt. Since the solubility of 1 transported by diffusion to the low-temperature region increases with temperature, the substrates are sequentially brought into contact with such a melt low-temperature region, where the melt becomes a supersaturated solution and can be precipitated in the low-temperature region. for example.

A growth layer of 5o-eoμm can be changed in a growth time of about 60 minutes.

As can be seen from FIG. 7, which shows the relationship between temperature and time, the temperature distribution is kept constant. Initially, the first substrate is in contact with the bottom of the P melt, and the p-type layer is grown.First, the slider is moved so that the first substrate is in contact with the bottom of the n-melt, and the second substrate is in contact with the bottom of the p-melt. do it like this. Therefore, respective growth layers are formed. In this way, a p-type layer is grown on the bottom and an n-type layer is grown on the top of the first substrate, thereby forming a diode. Such operations are repeated to perform epitaxial growth on a large number of substrates, and the composition of the growing crystal layer is monitored by optical excitation spectra, etc., without removing the substrates from the growth system, and the results are fed back via the control device 50. Good too.

Next, electrodes are attached to each of the p side and the n side and cut by one section to obtain a high brightness Ga1-xAlxAs light emitting diode (LED).

The preparation of P-melt and N-melt will be explained below.

Ga1. to be grown. Assuming that the desired composition X of the AtxAs epitaxial layer is determined, the control device 50 determines the growth temperature T° C. (the temperature of the substrate crystal or the temperature on the low temperature side of the melt) from the following equation.

T = α ・X 10 β ± 10%
(1) α=291.5, β=793.0
Weight ratio of solute in melt [^1]/[GaAs] -y
The value of is preferably within the range of 0.03 to 0.04. 2. The low temperature section at the bottom of the melt is set to the determined temperature, and the high temperature section is set to a temperature higher than the growth temperature by, for example, 10-50 DEG C.

When changing and adjusting the composition X of the grown crystal, the amount of change to be changed may be input into the control device 50 to automatically control the growth temperature T. The data forming the basis of this crystal growth method will be explained below. do.

The weight ratio of solute [8l]/[GaAs]-y is 0.0
The study focused on melts having a temperature of 3 to 0.04, particularly 0.037. Figure 1 shows the relationship (experimental data) between the composition X of the Ga1-x Alx As crystal measured by EPHA and the growth temperature T°C (temperature of the substrate crystal or temperature on the low temperature side of the melt). . FIG. 2 is EPHA data measured to determine the composition X in the crystal shown in FIG. 1, and shows the distribution of X in the growth thickness direction. As is clear from FIG. 1, the growth temperature dependence of X is almost constant, and these relationships can be approximated by the following equation.

X-γT+δ (2) γ-0
,00343δ=-2,6--2,9, that is, in the growth of Ga1-xAtxAs by the 1-temperature difference method, the composition X of the grown crystal is determined by the growth temperature T (°C), as shown in Figure 1. , this relationship can be used to determine growth conditions. therefore.

The growth temperature T (°C) is shown as follows.

T = α・X + β ± 10% (1) α=29
1.5, β=793.0 Therefore, the growth temperature T (℃)
can be determined from the desired composition X and formula (1).

There is a temperature distribution within the melt using the temperature difference method.

The material ^l, GaAs, melts in high temperature areas. The material consumed in the low-temperature section may be supplied in the high-temperature section.

In the temperature difference method, continuous growth on multiple substrates is possible, so the growing melt is mixed with the growing material (Al,
Contains enough growth material (not completely dissolved) to grow the required number of sheets in addition to the amount necessary to keep the melt in a saturated solution state (GaAs) is not completely dissolved. It is desirable, however, that this extra growth material is too much.

The growth material is present as microcrystals throughout the melt;
- The dissolved growth material precipitates on the microcrystal with the microcrystal as a nucleus, and prevents the necessary precipitation and growth on the substrate. For this reason, it is desirable to completely dissolve the solute at a temperature slightly higher than the high-temperature part, and not completely dissolve below this temperature.The amount of solute is determined from the solubility at a temperature 40-70℃ higher than the growth temperature. If you want to modify the composition X of the grown crystal using the same melt, which is preferable, input the current composition X and the modified composition X to the controller f50, find the change in the growth temperature to be modified, and 12- can also be automatically adjusted.

[Effects of the Invention] In the temperature difference method, it is not easy to accurately measure the temperature of the melt near the growing substrate.

Furthermore, it is difficult to accurately determine the growth temperature solely from the temperature of the furnace body, which uses local heaters and cooling gas to create temperature differences. In order to adjust to Ga with X
A 1-XAtxAs crystal is obtained. It can save a lot of time and effort and expensive materials, which is very useful.

[Brief explanation of the drawing]

Figure 1 shows the composition X in the temperature difference method liquid phase crystal growth according to the present invention.
A graph showing the relationship between growth temperature T and Figure 2 is EPHA measurement data.Figure 3 is a graph showing the relationship between crystal composition X obtained by slow cooling method and weight ratio of Ga to Ga [Al]/[Ga] in the melt. , Fig. 4 is a graph showing the saturated solubility of GaAs in a Ga-Al solution, Fig. 5 is a schematic diagram of the liquid phase crystal growth apparatus, Fig. 6 is a partially enlarged view of Fig. 5, and Fig. 7 shows the growth operation. 1 is a graph of temperature versus time to illustrate. Explanation of symbols 50 Control device 64, 6 with built-in computer
5.66 Melt tank 53 Slider 69 Board

Claims (1)

[Claims] (1) GaAl is produced by a temperature difference method in which a temperature difference is applied to a melt in which Al and GaAs are dissolved in a Ga solvent, and a substrate is brought into contact with the low temperature part of this melt to grow GaAlAs crystals.
In the As liquid phase crystal growth method, the crystal growth temperature T (℃
) is determined based on the desired composition x of the Ga_1_-_xAl_xAs crystal and T=α・x−β+10% α=291.5, β=793.0, a melt is prepared, and crystal growth is performed. GaAlAs liquid phase crystal growth method.