JPH01179794A - Liquid phase growth method for crystal of ga-al-as - Google Patents

Abstract

PURPOSE:To easily obtain a Ga1-xAlxAs crystal having a desired compsn. in liquid phase growth of the Ga1-xAlxAs crystal by a temp. difference method by determining the weight ratio of Al and Ga-As to be dissolved in a Ga solvent and the growth temp. by using the specific relation. CONSTITUTION:The following method is adopted in the liquid phase growth method of the Ga-Al-As crystal by the temp. difference method of providing a temp. difference to the melt prepd. by dissolving the Al and GaAs in the Ga solvent and bringing a substrate into contact with the low temp. part of this melt to grow the Ga-Al-As crystal: The weight ratio [Al]/[Ga-As]=y of the Al and GaAs to be dissolved in the Ga solvent and the growth temp. T( deg.C) are determined in accordance with the equation: x=A.T+B.log(y)+(C)(A =0.00343, B=0.64, C=-1.82) from the compsn. (x) of the desired Ga1-xAlxAs crystal and the melt is prepd., then the crystal growth is executed. The compsn. of the solute is determined in accordance with the growth temp. and the quantity of the solute is preferably determined in accordance with the temp. higher by 40-70 deg.C than the growth temp.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to crystal growth of GaAlAs, and in particular, to create a certain temperature difference in a melt in which a solute is dissolved, and to continuously transport the solute from a high temperature area to a low temperature area. This invention relates to liquid phase epitaxial crystal growth of GaAlAs by a temperature difference method in which crystals are grown in a low temperature region.

[Prior art] aa, -xAtxAs is a mixed crystal semiconductor whose band gap energy can be changed from 1.43 eV to 2.16 eV by changing the composition X (proportion of ^1^S) in the crystal. . Therefore, Ga1. Al, ^S is widely used as a material for light emitting diodes (LEDs) that emit light from infrared light to visible light. For example, to obtain a red LED with a wavelength of 660 nl, one light emitting layer of p-Ga1-x^1x is used.
X of AS is about 0.35. To obtain an LED with a wavelength of 780 nl, set X to approximately 0.15. To obtain an infrared LED with a wavelength of 850 nn, X should be approximately 0.01, therefore.

In a GaAlAs LED, X of p-GaAlAs is determined depending on the target emission wavelength. n-Ga1-1-× × X of Al As is also not constant, and the target emission wavelength x
It can be determined depending on ×. n-Ga1. X of AlxAs
is Kano Ga1. ^1xAsq To confine electrons and holes in the optical layer, or p-Ga1-xAtxAs
A value is selected that is necessary to effectively guide light emitted from the layer to the outside of the crystal without absorbing it. For example, p-Ga1. AlxAs
When the X of n-Ga, -xAtxAs is selected to be 0.6-0.85.

The active region of an LED is usually made by epitaxial growth on a substrate crystal. As a substrate crystal, it is desirable to obtain one that is not expensive, has a large diameter, and has good crystallinity.The Ga1-x^I,As mixed crystal covers the entire range of composition X, and has little lattice mismatch with the GaAs crystal, so , a high-quality Ga1. AlxAs can be epitaxially grown. For these reasons, GaAlAs is currently widely used as a light emitting diode with high brightness and high output from infrared light to red light.

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

A slow cooling method, a temperature difference method, and the like are known as liquid phase crystal growth methods. The slow cooling method is a method in which the 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.
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. By this method, a light emitting diode with an excellent characteristic of 1. Lasers etc. are being manufactured.

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

However, in the liquid phase crystal growth of Ga1-xAtxAs by the temperature difference method, no clear relationship has been found between the melt composition and the crystal composition, and when trying to obtain the desired crystal composition The experiment had to be repeated.

The object of the present invention is to obtain Ga1-xAtxA of desired composition X.
An object of the present invention is to provide a crystal growth technique by which s-crystals can be easily obtained.

[Study carried out to solve the problem] Generally, the composition X of Ga1-x41xAS crystal grown by liquid phase growth is determined by the concentration of A1 in the solution (melt). In the slow cooling method, which is widely used as a liquid phase epitaxial growth method, for example, 1) 19685YHPO8IU
Hon GaAs, paper 12) Jap, J.
Appl, Phys, Vol, 18. no, 8, 19
79. A1 in solution as shown on p1509
It is known that a certain relationship exists between the concentration of and the composition X of the growing Ga1-x^1x AS crystal. This relationship is reproduced in FIGS. 2 and 3. Using these, the materials A1 and GaAs and the solvent Ga
The amount of can be easily determined. Specifically, the desired Ga1. Using the composition X of the ^1x AS crystal and the growth temperature, which is the temperature of the melt low-temperature part or the substrate, from Figure 2, the weight ratio of A1 in the molten GaGa [^I]
/[Get Gal. From FIG. 3, which shows the saturation solubility of GaAs in an Al-Ga solution using [Al1/[Gal and growth temperature], the amount of GaAs dissolved is
The weight ratio of GaAs to [GaAs1/[Gal] is determined as [GaAs1/[Gal]. This [Al1 /lGa1 and [Ga
As]/[Gal, the amount of each material is weighed out to form a growth melt.

The present inventors used the method proposed by this slow cooling method to
- The composition X of the crystal grown by temperature difference liquid phase epitaxial growth was measured using Ef'14A.

Figure 4 shows the measurement results, and the solid line is not reproduced from Figure 2.
] and X. As is clear from the data plot, the weight ratio of composition X and A1 to Ga in the melt [Al]/
No relationship is found between [Ga] and However, in a method similar to the slow cooling method, G a i -x A l x A S with the desired composition
It turned out that it was not possible to obtain crystals.

The present inventors conducted many more experiments and found that there is a certain relationship in liquid phase epitaxial crystal growth using the temperature difference method, which is different from that in the slow cooling method.

It has been confirmed that utilizing this relationship is extremely useful when growing GaA I^S crystals by liquid phase crystal growth using a temperature difference method.

[Means for solving the problem] In the liquid phase crystal growth of Ga1-x Alx As by the temperature difference method, the relationship shown in Fig. 1 holds, and the weight ratio of A1 and GaAs dissolved in the melt IAl ]/
[GaAs0 amount y and growth temperature T are the growing Ga1-x
It is expressed by the composition X of the AlxAs crystal and a certain formula. Namely.

X, = A-T+B・log(y) 〇,
(1) A=0.00343, B=0.64.
It is sufficient to determine y and T according to C=-1,82°.

Furthermore, the solute composition is determined based on the growth temperature.

Preferably, the amount of solute is determined based on a temperature 40-70°C higher than the growth temperature.

[Effect] This was discovered in the liquid phase growth of G a 1-x A I x AS by the temperature difference method. It is expressed by equation (1).

Since the melt composition y and growth temperature T are determined using natural laws different from the slow cooling method, Ga1-x with the desired composition
A1xAS crystal can be grown.

Furthermore, G at a temperature 40-70°C higher than the growth temperature
The saturation solubility of 5As is determined, the amount of A1 corresponding to the weight of GaAs according to the above [Al]/[GaAs]・y is determined, and a melt is prepared. A solute suitable for continuous growth =
You can make a melt containing 7- sauce. If the solute is adjusted to the saturation solubility at a temperature slightly higher than the high temperature part of the melt, the solute will not completely dissolve in the high temperature part.

It is sequentially dissolved as the epitaxial layer grows.

[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 carrying a semiconductor substrate is housed in the entrance side preliminary chamber 51, and is successively pushed up through the gate pulp 62 by the slider push-up mechanism 55. 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 cause crystal growth.

The slider carrying the substrate on which crystal growth has been completed is sent out of the growth chamber 57 via the gate valve 73, and is stored in the exit-side preliminary chamber 79 by the slider receiving mechanism 77 via the gate valve 74. It will be done. Each drive mechanism 55, 6
1.77, heaters 59, 67, etc. can be controlled by the control device 50. The control device 5o further stores Equation (1) and its modified forms, and can calculate each parameter, display instructions to the operator based on the results, perform automatic control, etc., as necessary.

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 solvent, 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 to 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 an aal, AtxAs light emitting diode, the AlAs composition ratio X should be approximately 0.3 in the p-type region.
5. A1 so that it is approximately 0°6-0.85 in the n-type region
A temperature difference in the vertical direction is set in the root tank 65.6e as shown on the right side of the figure. For example, a temperature difference of 10°C to 60°C is provided at a temperature of 850°C to 950°C. In order to continuously supply the solute, the solute may be floated above the melt, which is a high-temperature part, or a solute containing part may be created and brought into contact with the melt.
The solute dissolves to saturation solubility in the high temperature region and is transported to the low temperature region by the temperature gradient and diffusion.

Since the solubility usually increases with temperature, it becomes a supersaturated solution in a low temperature region, and is in a state where it can be precipitated. The substrates are sequentially brought into contact with such melt low temperature parts.

For example, a growth layer of 50-60 μm can be changed in about 60 minutes of growth time. As can be seen from FIG. 7, which shows the relationship between temperature and time, the temperature distribution is kept constant.

At first, the first substrate is in contact with the bottom of the p-melt, and a p-type layer is grown, then 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. make contact with them. Therefore, respective growth layers are formed. Now, on the first substrate, a P-type layer is grown on the bottom and an N-type layer is grown on top, forming one diode. Such operations are repeated to perform epitaxial growth on a large number of substrates, and the composition of the grown crystal layer is monitored using optical excitation spectra, etc., without removing the substrates from the growth system, and the results are fed back via the control device 50. You can.

Next, an electrode was placed on each pflln side and cut into 1 section to form a high-brightness Ga1-x^1xAs light emitting diode (LED).
).

The preparation of p-melt and n-melt will be explained below.

Assuming that the desired composition
]-y Mana determines the growth temperature T''C (temperature of the substrate crystal or temperature on the low temperature side of the melt) from the following equation.

x=A−T×B−l og(V)×(
1) A=0.00343, B=0.64, C
=-1,82 This determines the growth temperature T and the solute weight ratio y. For example, growth temperature T = 900 ('C)
In the case of.

x= 0.00343x900 +0.64100(3
') 1.82-'-y =0.011 eXD(
3,6x), the weight ratio y of the solute can be determined.

Next, the solubility of GaAs in the A1-Ga solution at a temperature 40-70°C higher than the growth temperature, for example, about 60°C higher than the growth temperature, and the [A1]/[Ga
As] and [GaAs] / [Ga], [Al] /
[Ga] can be determined. In addition, A dissolved in Ga solvent
1 and GaAs weight ratio [A l ]/[GaAs1=
V is preferably 0.015-0.3.

- When changing and adjusting the composition X of the crystal grown from the previously created melt, the growth temperature T may be controlled via the control device 5o.

The data underlying this crystal growth method are explained below.

Figure 1 shows the summarized data, and the following elements will be explained separately.

Figure 8 shows the weight ratio of A1 and GaAs dissolved in the melt [
^1]/[GaAs1=y and Gl, which cannot be obtained at a growth temperature of 900°C by temperature difference method liquid phase epitaxial growth, ^1
2 is a plot of experimental data showing an example of the relationship with the composition X of xAs crystal. This relationship can be approximated by the following equation.

X=α・+oa(y) 1β±10% (
2) α=0.64, β=1.27.

In the range of O≦x<0.1 and 0.85<x≦1.0,
As shown by the broken line, the relationship deviates from this equation. However, even within this range, it is relatively easy to predict the solute weight ratio [Al]/[GaAs] = y necessary to obtain a crystal with the desired composition X.

FIG. 9 shows EPHA data measured to determine the composition X in the crystal shown in FIG. 8, and shows the distribution of X in the growth thickness direction.

FIG. 10 shows Ga1. measured by EPHA. AtxA
This is an experimental data plot showing the relationship between the composition X of the s crystal and the growth temperature T'C (the temperature of the substrate crystal or the temperature of the low temperature part of the melt), and the weight ratio of A1 and GaAs dissolved in the melt [Al]/[ GaAs1=y is shown as a parameter. The growth temperature dependence of X is almost constant at each value of the weight ratio [Al]/[GaAs]·y of Al and GaAs, and these relationships can be approximated by the following equation.

X-γ・T+δ (3
) γ=0.00343 δ=-2,6~-2,
9 Figures 8 and 10 are combined into one composition X (^1^S
) is on the Z axis, and the growth temperature T ('C) is on the X axis.

FIG. 1 shows the solute weight ratio [Al]/[GaAs]·y expressed on the y-axis.

In the liquid phase crystal growth of Ga1-x^1xAs by the temperature difference method, as shown in Figure 1, the composition X of the growing crystal is the growth temperature H'C) and the solute weight ratio y-[Al]/[GaAs ]
This relationship can be used to determine growth conditions. The relationship shown in FIG. 1 can be expressed by a linear equation.

x=A −T×B ・l0Q(y) +C(1)A=0
．． 00343, B-0,64, C--1,82 Therefore, the growth temperature T ('C) and the ^1 and Ga dissolved in the melt
The weight ratio of As [Al]/[GaAs]-V is the desired G
a1゜^s It can be determined from the composition X of Al and formula (1).

The above discussion has been about crystal growth that takes place in the low-temperature part of the melt. There is a temperature distribution within the melt using the temperature difference method,
The materials Al and GaAs melt at high temperatures.

In the temperature difference method, continuous growth on multiple substrates is possible, so the growing melt is the growing material (^l,
GaAs) is not completely dissolved.

In addition to the amount necessary to keep the melt in a saturated solution,
It is desirable to contain enough growth material (not completely dissolved) to grow the required number of sheets, but if this excess growth material is too much.

The growth material is present as microcrystals throughout the melt;
- The dissolved growth material precipitates on the microcrystals as nuclei, which may hinder the necessary precipitation and growth on the substrate. For this reason, it is preferable to determine the amount of solute based on the solubility at a temperature 40 to 70° C. higher than the growth temperature.

For example, if the temperature of the substrate is about 900℃ and the melt is 1o
Assuming a temperature difference of -so°C, for example, it will completely melt at a temperature slightly higher than the high temperature part, for example, about 960°C, and will not completely melt below this temperature, i.e.
Assuming the growth temperature is 900℃, it will dissolve in the melt ^
From the desired aal, Atx As crystal weight ratio y=[^1]/[GaAs] and the growth temperature T, the composition
In Figure 3, the cubic order determined by calculation using [^
1], / [GaAs] line (dashed line) and [G at 960°C
aAs1 / [Gal vs. [Al] / [Gal line (solid line)
Find [GaAs]/[Gal from the y value of the intersection with This [GaAs]/[Gal and [8II/[Gal
The amount of each material relative to the solvent Ga is calculated from the total amount of Ga. The amount of solute determined in this way completely dissolves at 960°C. In other words, since the substrate temperature is 900℃ and the melt has a temperature difference of 10-50℃, the substrate temperature (900℃)
It completely dissolves at a temperature (960 degrees Celsius) of 10 degrees Celsius and 00 degrees Celsius temperature difference (50 degrees Celsius), but it does not completely dissolve below this temperature.
This ensures a source of solutes.

When a crystal is grown using a melt containing each material (GaAs, Ga, Al) obtained by this method at about 900°C with a temperature difference of 10-50°C, the composition Ga, AtxAs crystals are obtained.

If the composition X of the grown crystal is not corrected using the same melt, the current composition X and the corrected composition X are input to the control device 50, the change in the growth temperature to be corrected is determined, and the heater is automatically adjusted. You can also do it.

[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, since local heaters and cooling gas are used to create temperature differences, it is difficult to accurately determine the growth temperature from only the temperature of the furnace body. In addition, there are variations in each growth system, so in order to precisely match the desired composition
] etc. 1 The method of the present invention has to adjust Ga1-x^1x with accurate composition X within about 10%.
As crystals are obtained. It can save a lot of time and effort and expensive materials, which is very useful.

[Brief explanation of the drawing]

Fig. 1 is a graph showing the relationship between each parameter in the temperature difference method liquid phase crystal growth according to the present invention, and Fig. 2 is a graph showing the relationship between each parameter in the temperature difference method liquid phase crystal growth according to the present invention.
/[Ga], Figure 3 is a graph showing the saturation solubility of GaAs in a Ga-Al hot solution, and Figure 4 is a graph showing the composition X in the crystal versus the weight ratio of A1 and Ga in the melt [^
1]/[Ga], a graph comparing the slow cooling method and the temperature difference method. Figure 5 is a schematic diagram of a liquid phase crystal growth apparatus using the temperature difference method. Figure 6 is a partially enlarged view of Figure 5. Figure 7 is a graph of temperature versus time to explain the growth operation, and Figure 8 is a graph of composition X versus [Al]/[GaAs] in the melt in the temperature difference method.
Weight ratio graph, Figure 9 is EPH^ measurement data, 1st
FIG. 0 is a graph showing the relationship between composition X and growth temperature T using the [Al]/[GaAs] weight ratio as a parameter. Explanation of symbols 50 Control device 64, 6 with built-in computer
5.66 Melt tank 53 Slider 69 Substrate IP P-type layer IN on the first substrate
N-type layer 2P on the first substrate P-type layer 28 on the second substrate N-type layer on the second substrate

Claims (2)

[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.
Ga_1_-_xAl_xA desired weight ratio of Al and GaAs dissolved in Ga solvent [Al]/[GaAs]=y and growth temperature T°C in a liquid phase crystal growth method of As
Determine the composition of the S crystal based on x and x = A・T+B・10g(y)+C A=0.00343, B=0.64, C=-1.82, prepare the melt, and grow the crystal. A method for growing GaAlAs liquid phase crystals, characterized by: (2) In the GaAlAs liquid phase crystal growth method according to claim 1, the GaAlAs in an Al-Ga solution at a temperature 40 to 70° C. higher than the growth temperature T.
A method of producing GaAlAs characterized by determining the weight ratio [GaAs]/[Ga] of GaAs and Ga from the solubility of s and the determined [Al]/[GaAs]=y, preparing a melt, and performing crystal growth. Liquid phase crystal growth method.