JPH0477715B2 - - 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 bandgap 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 high-brightness, high-output light emitting diode that emits light ranging from infrared light to red light. Ga _1-x as such a light emitting device
When using Al _x As, it is an important issue to control the composition x in terms of emission wavelength, external luminous efficiency, etc.

As a liquid phase crystal growth method, slow cooling method, 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 then 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,
80℃-1000℃, preferably 850℃-950℃ and 10℃-
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 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 Ga _1-x Al _x As, no clear relationship has been found between the growth temperature and the crystal composition x. The experiment had to be repeated.

The purpose of the present invention is to obtain Ga _1-x Al _x As with a desired composition.
An object of the present invention is to provide a crystal growth method that allows 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 1507, it is known that a certain relationship exists between the Al concentration in the solution and the composition x of the growing Ga _1-x Al _x As crystal. This relationship is reproduced in FIGS. 3 and 4. Using these, the amounts of Al and GaAs as materials and Ga as a solvent can be easily determined depending on the composition x and growth temperature of the Ga _1-x Al _x As crystal to be grown. Specifically, it may be done as follows. Desired Ga _1-x Al _x As crystal composition x
The weight ratio [Al]/[Ga] of Al to the solvent Ga is obtained from FIG. This [Al]/[Ga]
and growth temperature for Al-Ga solution.
Dissolved from Figure 4 showing the saturation solubility of GaAs
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.

However, in the temperature difference liquid phase epitaxial growth method, the relationship between x and growth temperature as in the slow cooling method is not established, and in a method similar to the slow cooling method, Ga _1-x with the desired composition x is Unable to obtain Al _x As crystals. The present inventors further conducted many experiments and found that there is a certain relationship in the temperature difference liquid phase epitaxial growth method that is different from that in the slow cooling method. We have confirmed that utilizing this relationship is extremely useful when growing Ga _1-x Al _x As crystals by temperature difference method liquid phase epitaxial growth.

[Means for solving the problem] In the temperature difference method liquid phase crystal growth of Ga _1-x Al _x As, the relationship shown in Figure 1 holds, and the weight ratio of Al and GaAs dissolved in the melt is [Al]/
If [GaAs]=y is constant, the growth temperature T has a relation to the composition x of the growing Ga _1-x Al _x As crystal expressed by a constant formula. That is, T can be determined according to T=α・x+β±10% (1) α=291.5, β=793.0.

[Function] The growth temperature is determined by utilizing the natural law found in the liquid phase crystal growth of Ga _1-x Al _x As by the temperature difference method, which is different from the slow cooling method, so that the desired composition
An epitaxial layer of Ga _1-x Al _x As can be grown.

[Example] FIG. 5 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. 6 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 adjusted to be equal to the amount of Al in the p-melt tank 6.
It is preferable that the amount of Al be greater than the amount of Al in 5. for example,
To obtain a red-emitting Ga _1-x Al _x As light-emitting diode, the composition x should be approximately 0.35 in the p-type region and approximately 0.35 in the n-type region.
The amounts of Al and GaAs are determined to be 0.6−0.85.
A vertical temperature difference is set in both melt tanks 65 and 66 as shown on the right side of the figure. For example, 850
Set the temperature difference between 10℃ and 60℃ at a temperature of ℃−950℃.
In order to continuously supply the solute, the solute may be floated above the melt, which is a high temperature section, or a solute containing section 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 precipitate. The substrates are sequentially brought into contact with such melt low temperature parts. For example, with a growth time of about 60 minutes, 50−
A growth layer of 60 μm is obtained.

FIG. 7 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. The composition of the growing crystal layer can be monitored using optical excitation spectra, etc. without taking the substrate out of the growth system, and the results can be sent to the control device 5.
0 may also be used for feedback.

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.

The controller 5 assumes that the desired composition x of the Ga _1-x Al _x As epitaxial layer to be grown is determined.
0 is the growth temperature T° C. (temperature of the substrate crystal or temperature on the low temperature side of the melt) determined from the following equation.

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

When changing and adjusting the composition x of the grown crystal, the amount of change to be changed may be input to the control device 50 to automatically control the growth temperature T.

The data underlying this crystal growth method are explained below. The weight ratio of solute [Al]/[GaAs] = y is
The study focused on melts with a value of 0.03 to 0.04, especially 0.037. Figure 1 shows the composition x of Ga1−xAlxAs crystal.
This figure shows the relationship (experimental data) between the results measured by EPMA and the growth temperature T°C (the temperature of the substrate crystal or the temperature on the low temperature side of the melt). Second
The figure shows the distribution of x in the growth thickness direction using EPMA data measured to determine the composition x in the crystal shown in Figure 1. 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=0.00343 δ=−2.6−−2.9 In other words, in the growth of Ga _1-x Al _x As by the temperature difference method, as shown in Figure 1, the composition x of the grown crystal is
is determined by the growth temperature T (° C.), and the growth conditions can be determined using this relationship. Therefore,
The growth temperature T (°C) is shown as follows.

T=α・x+β±10% (1) α=291.5, β=793.0 Therefore, the growth temperature T (℃) is determined by the desired composition x and the formula
It can be obtained from (1).

There is a temperature distribution in the melt created by the temperature difference method, and the materials Al and GaAs melt in the high temperature area.
The material consumed in the low-temperature section may be supplied in the high-temperature section. In the temperature difference method, continuous growth is possible on multiple substrates, so the melt during growth is not in a state in which the growth materials (Al, GaAs) are completely dissolved, but in a saturated solution state. In addition to the amount required for this, 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 exist as microcrystals throughout the melt, and once melted, the growth material will precipitate on the microcrystals using the microcrystals as nuclei, causing precipitation on the necessary substrate. , hinders growth. For this reason, it is desirable to completely melt at a temperature slightly higher than the high-temperature portion, and not to completely melt at temperatures below this temperature. Preferably, the amount of solute is determined from the solubility at a temperature 40-70°C higher than the growth temperature. When it is desired to correct the composition x of the grown crystal 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.

[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
The weight ratio of Al/GaAs, etc. had to be adjusted. In the method of the present invention, Ga _1-x Al _x As having an accurate composition x can be easily obtained by adjusting the set temperature of the furnace body.
Crystals are obtained. 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 showing the relationship between composition x and growth temperature T in temperature difference method liquid phase crystal growth according to the present invention;
The figure shows EPMA measurement data, Figure 3 is a graph showing the relationship between the crystal composition x measured by the slow cooling method and the Al to Ga weight ratio [Al]/[Ga] of the melt, and Figure 4 is
A graph showing the saturation solubility of GaAs in a Ga-Al solution, Figure 5 is a schematic diagram of a liquid phase crystal growth apparatus, Figure 6 is a partially enlarged view of Figure 5, and Figure 7 is a temperature versus time explanation of the growth operation. This is a graph of Explanation of symbols, 50... Control device with built-in computer, 64, 65, 66... Melt tank, 53...
Slider, 69...Substrate, 1P...P-type layer on the first substrate, 1N...N-type layer on the first substrate, 2P
...p-type layer on the second substrate, 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 phase crystal growth method, the desired crystal growth temperature T (℃) is the Ga _1-x Al _x As crystal composition x
and T=α・x−β+10% α=291.5, β=793.0, and crystal growth is performed by preparing a melt.