JPH0477716B2 - - Google Patents

Description

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

[Prior art] Ga _1-x Al _x As is the composition x in the crystal (proportion of AlAs)
It is a mixed crystal semiconductor whose band gap energy can be changed from 1.43eV to 2.16eV by changing the . Therefore, Ga _1-x Al _x As is widely used as a material for light emitting diodes (LEDs) that emit light from infrared to visible light. For example, the wavelength
To obtain a 660nm red LED, the P-
For Ga _1-x Al _x As, x should be about 0.35, x should be about 0.15 to obtain an LED with a wavelength of 780 nm, and x should be about 0.01 to obtain an infrared LED with a wavelength of 850 nm. Therefore,
In a GaAlAs LED, x in p-Ga _1-x Al _x As is determined depending on the target emission wavelength. n
-Ga _1-x Al _{x x} in As is also not constant and is determined depending on the target emission wavelength. The x in n-Ga _1-x Al _x As is used to confine electrons and holes in the p-Ga _1-x Al _x As light-emitting layer, or the x in p-Ga _1-x Al _x As
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-Ga _1-x
If x of Al _x As is 0.35, then x of n-Ga _1-x Al _x As is
It is chosen to be 0.6−0.85.

The active region of an LED is usually produced 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 _1-x Al _x As mixed crystal has little lattice mismatch with the GaAs crystal over the entire range of composition x. Therefore, it is possible to epitaxially grow high-quality Ga _1-x Al _x As on a GaAs substrate, which provides a large diameter and high-quality crystal. 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. Ga _1-x Al _x as such a light emitting device
When using As, it is an important issue to control the composition x in terms of emission wavelength, external emission efficiency, etc.

As a liquid phase crystal growth method, a slow cooling method, a temperature difference method, etc. are known. 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. This refers to a method in which a solute is dissolved (supplied) in a high-temperature section, transported to a low-temperature section by temperature gradient and diffusion, and the solute is precipitated from a supersaturated solution in the low-temperature section. In other words, in the temperature difference method liquid phase crystal growth, growth is performed at a constant temperature rather than gradually lowering the temperature as in the slow cooling method, so there is less occurrence of crystal defects and fluctuations in crystal composition and impurity concentration due to temperature changes. . It can also grow in large numbers in succession. In the case of GaAlAs-based crystals, a melt made of Ga solution is placed in a melt bath made of graphite,
10℃ at 800℃-1000℃, preferably 850℃-950℃
Crystal growth is performed with a temperature difference of -60°C. Using this method, light emitting diodes, lasers, etc. with excellent characteristics are 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 liquid phase crystal growth of Ga _1-x Al _x As using the temperature difference method, no clear relationship has been found between melt formation and crystal composition, and it is difficult to obtain the desired crystal composition x. In order to do this, we had to repeat many experiments.

The object of the present invention is to obtain Ga _1-x Al _x with a desired composition x.
The object of the present invention is to provide a crystal growth technique that allows As crystals to be easily obtained.

[Study conducted to solve the problem] Ga _1-x, which is generally grown by liquid phase growth method
It is the concentration of Al in the solution (melt) that determines the composition x of the Al _x As crystal. In the slow cooling method, which is widely used as a liquid phase epitaxial growth method,
For example, (1) 1968 SYMPOSIUM on GaAs, paper 1 (2) Jap.J.Appl.Phys, Vol. 18, no. 8, 1979,
As shown on page 1509, it is known that a certain relationship exists between the concentration of Al in the solution and the composition x of the growing Ga _1-x Al _x As crystal. This relationship is reproduced in FIGS. 7 and 8. Using these, _the materials Al and GaAs and _the solvent Ga
The amount of can be easily determined. Specifically, it may be done as follows. The weight ratio [Al]/[Ga] of Al to the solvent Ga is obtained from FIG. 7 using the desired composition x of the Ga _1-x Al _x As crystal and the growth temperature which is the temperature of the melt low temperature section or the substrate. This [Al]/
Dissolved from Figure 8, which shows the saturation solubility of GaAs in Al-Ga solution using [Ga] and growth temperature.
The amount of GaAs is determined as the weight ratio of GaAs to solvent Ga: [GaAs]/[Ga]. The amount of each material from [Al]/[Ga] and [GaAs]/[Ga] is weighed to form a growth melt.

The present inventors weighed the material using the method proposed for this slow cooling method and measured the composition x of the crystal grown by temperature difference method liquid phase epitaxial growth using EPMA. Figure 3 shows the measurement results. The solid line is the relationship between [Al]/[Ga] and x at a growth temperature of 900° C. in the case of the slow cooling method reproduced from FIG. As is clear from the data plot, composition x Al and Ga in the melt
No relationship was found between the weight ratio [Al]/[Ga] and the weight ratio [Al]/[Ga]. In this way, in the temperature difference method liquid phase epitaxial growth, there is no fixed relationship between the weight ratio [Al]/[Ga] and x as in the slow cooling method, and in a method similar to the slow cooling method, it is difficult to obtain the desired composition x.
It was found that it was not possible to obtain a Ga _1-x Al _x As crystal.

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.
We have confirmed that utilizing this relationship is extremely useful when growing GaAlAs crystals by liquid phase crystal growth using the temperature difference method.

[Means for solving the problem] In the liquid phase crystal growth of Ga _1-x Al _x As using the temperature difference method, the relationship shown in Figure 1 holds, and the weights of Al and GaAs dissolved in the melt are The ratio [Al]/[GaAs]=y is the growing Ga _1-x Al _x As
There is a relationship expressed by a certain formula with the crystal composition x.
That is, y can be determined according to y=α・exp(+β・x)±10% (1) α=0.011, β=3.5.

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

Furthermore, find the saturation solubility of GaAs at a temperature 40-70°C higher than the growth temperature, and follow the above-mentioned [Al]/[GaAs] = y, which corresponds to the weight of GaAs.
By determining the amount of Al and preparing the melt, a melt containing a solute source suitable for continuous growth can be created. If the saturation solubility is adjusted to a temperature slightly higher than the set high temperature part of the melt, the solute will not be completely dissolved in the high temperature part, but will gradually dissolve as the epitaxial layer grows.

[Operation] Melt formation is determined by utilizing the natural law found in the liquid phase crystal growth of Ga _1-x Al _x As using the temperature difference method, which is different from the slow cooling method, so Ga _1-x with the desired composition is determined. _x Al _x As crystals can be grown.

[Example] FIG. 4 schematically shows an example of a temperature difference method liquid phase growth apparatus. The 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 valve 62 by a slider pushing up mechanism. Preferably, the inlet side preliminary chamber 51 is preheated in a preliminary heating furnace 59. The pushed-up slider is sent into the growth chamber 57 through the gate valve 63 by the slider drive mechanism 61. A melt tank 64 is located inside the growth chamber 57.
is provided, and a 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. The drive mechanisms 55, 61, 77, heaters 59, 67, etc. can be controlled by the control device 50. The control device 50 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. 5 is an enlarged explanatory view of one example of the melt tank 64 portion. Solutes Al and GaAs in the solvent Ga
is melted, and the p melt tank 65 and the n melt tank 66
is housed in. Furthermore, as impurities, Zn is dissolved in the P melt tank 65 and Te is dissolved in the N melt tank 66. In order to make the bandgap of the n-type region that will grow later larger than that of the p-type region, the amount of Al in the n-melt tank 66 is set to be equal to that of the p-melt tank 65.
It is better to make the amount of Al larger than the amount of Al. For example, to obtain a red-emitting Ga _1-x Al _x As light-emitting diode,
The amounts of Al and GaAs are determined so that the AlAs composition ratio x is about 0.35 in the p-type region and about 0.6-0.85 in the n-type region. A vertical temperature difference is set in both melt tanks 65 and 66 as shown on the right side of the figure. For example, a temperature difference of 10°C to 60°C is set between 850°C and 950°C. To continuously supply the solute, the solute is floated above the melt, which is a high-temperature part, or a solute storage part is created and brought into contact with the melt. The solute dissolves to saturation solubility in the high temperature section and is transported to the low temperature section by 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 precipitate. The substrates are sequentially brought into contact with such melt low temperature parts.
For example, a growth layer of 50-60 μm can be obtained with a growth time of about 60 minutes.

FIG. 6 shows the relationship between temperature and time. As can be seen from the figure, the temperature distribution remains constant. Initially, the first substrate contacts the bottom of the p-melt and grows a p-type layer. Next, move the slider so that the first board is n
touch the bottom of the melt, and the second substrate touches the bottom of the p-melt. 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.

Next, electrodes are attached to the p side and the n side, and separated and cut to create a high brightness Ga _1-x Al _x As light emitting diode (LED).
get.

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

Assuming that the desired composition x of the Ga _1-x Al _x As epitaxial layer to be grown is determined, the controller 50 determines the weight ratio of Al and GaAs dissolved in the Ga solvent [Al]/[GaAs]=y is determined from the following formula.

y=α・exp(+β・x)±10% (1) α=0.001, β=3.5, However, the weight ratio of dissolved Al and GaAs [Al]/
[GaAs]=y is 0.015−0.3.

The data underlying this crystal growth method are explained below.

Figure 1 shows the weight ratio of Al and GaAs dissolved in the melt [Al]/[GaAs] = y and the composition x of Ga _1-x Al _x As crystal obtained by temperature difference method liquid phase epitaxial growth. The relationship with the results measured by (experimental data at a growth temperature of 900°C) is shown. This relationship can be approximated by the following equation.

y=α・exp(+β・x)±10% (1) In the range of α=0.001, β=3.5, 0≦x<0.1 and 0.85<x≦1.0, the relationship of this equation deviates as shown by the broken line. come. However, even within this range, the desired composition x from Figure 1
Weight ratio of solute necessary to obtain crystals [Al]/
It is relatively easy to predict that [GaAs]=y.

Figure 2 shows EPMA data measured to determine the composition x in the crystal shown in Figure 1, and shows the distribution of x in the growth thickness direction.

In the growth of GaAlAs by the temperature difference method, as shown in FIG. 1, the composition x in the growing crystal is determined by the solute weight ratio y=[Al]/[GaAs]. Therefore, the weight ratio of Al and GaAs dissolved in the melt [Al]/
[GaAs] = y is the desired Ga _1-x Al _x As crystal composition x
(preferably 0.1≦x≦0.85) and equation (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 measured by the temperature difference method. The materials Al and GaAs melt in high temperature areas.

In the temperature difference method, it is possible to grow many sheets continuously, so the growing melt is mixed with the growing material (Al,
In addition to the amount necessary to keep the melt in a saturated solution rather than a completely dissolved state (GaAs),
It is desirable to include a sufficient amount of growth material (not completely dissolved) to grow the required number of sheets.
However, if there is too much of this extra growth material, the growth material will be present as microcrystals throughout the melt;
Once melted, the growth material precipitates on the microcrystals as nuclei, which may prevent the necessary precipitation and growth on the substrate. For this reason, the growth temperature
It is preferable to determine the amount of solute based on its solubility at a temperature 40-70°C higher.

For example, the temperature of the board is about 900℃, and it melts.
Assuming a temperature difference of 10-50°C, it is desirable to completely melt at a temperature slightly higher than the high-temperature part, for example, about 960°C, and not to completely melt below this temperature.

In other words, the desired weight ratio of Al and GaAs dissolved in the melt y=[Al]/[GaAs]Ga _1-x Al _x As
Formula from crystal composition x (preferably 0.1≦x≦0.85)
Determined based on (1). Next, in Figure 8, the equal [Al]/[GaAs] line (dashed line) and the [GaAs]/[Ga] versus [Al]/[Ga] line (solid line) at 960°C.
Find [GaAs]/[Ga] from the value of the vertical axis at the intersection with . This [GaAs]/[Ga] and [Al]/[Ga]
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 is
It completely melts at 960℃. Assuming that the temperature of the substrate is 900℃, since there is a temperature difference of 10-50℃ in the melt, it will completely melt at the substrate temperature (900℃ + temperature difference (50℃) + α temperature (960℃), and this This ensures a source of solutes. Each material obtained in this way (GaAs, Ga,
Using a melt containing Al), the temperature difference is 10− at approximately 900℃.
When growing a crystal at 50℃, from the desired x, ± approx.
A Ga _1-x Al _x As crystal with a composition x within 10% is obtained. Note that these operations may be programmed and stored in the control device 50 built into the computer, so that the operator only has to input the desired crystal composition x, etc.

[Effect 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. Furthermore, there are variations in each growth system, and therefore it is necessary to repeat GaAs/Ga or
Al/GaAs etc. had to be adjusted. The method of the present invention yields Ga _1-x Al _x As crystals with a precise composition x within ±about 10%. It can save a lot of time and effort and expensive materials, which is very useful.

[Brief explanation of drawings]

Figure 1 is a graph of composition x versus weight ratio of [Al]/[GaAs] in the melt in the temperature difference method, Figure 2
EPMA measurement data, Figure 3 shows the composition x in the crystal
A graph comparing the slow cooling method and the temperature difference method in relation to the weight ratio [Al]/[Ga] of Al and Ga in the melt, Figure 4 is a schematic diagram of the liquid phase crystal growth apparatus, and Figure 5 is the A partially enlarged view of the figure, Figure 6 is a graph of temperature versus time to explain the growth operation, and Figure 7 is a graph of crystal composition x vs. weight ratio of Al to Ga in the melt [Al]/
FIG. 8 is a graph showing the relationship between [Ga] and the saturated solubility of GaAs in a Ga-Al solution. Explanation of symbols, 50... Control device with built-in computer, 64... Melt tank, 65... Melt tank, 6
6...melt tank, 53...slider, 69...substrate, 1P...p-type layer on the first substrate, 1N...1
N-type layer on the second substrate, 2P...P on the second substrate
Type layer, 2N...N type layer on the second substrate.

Claims (1)

[Claims] 1. 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 GaAlAs liquid crystal growth method, the weight ratio of Al and GaAs dissolved in Ga solvent [Al]/[GaAs] = y
Determine the composition of the desired Ga _1-x Al _x As crystal based on x and y=α・exp(+β・x)±10% α=0.011, β=3.5, prepare the melt and start crystal growth. A method for liquid phase crystal growth of GaAlAs. 2. A method for growing a liquid phase crystal of GaAlAs according to claim 1, in which a method for growing an Al-Ga solution at a temperature approximately 40 to 70°C higher than the growth temperature T is provided.
Solubility of GaAs and determined weight ratio y = [Al]/
[GaAs] to GaAs to Ga weight ratio [GaAs]/
A GaAlAs liquid phase crystal growth method characterized by determining [Ga], preparing a melt, and performing crystal growth.