JPS6357398B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a crystal growth method and an apparatus thereof, and particularly relates to a method and apparatus for growing a Ga _1-x Al _x As mixed single crystal by a solution method. be.

[Prior art] Compound semiconductor mixed crystals such as Ga _1-x Al _x As are used in various applications such as light emitting diodes and semiconductor lasers, and these mixed single crystals of GaAlAs have similar lattice constants. Crystals are generally grown on GaAs substrates by liquid-phase epitaxial growth using the slide boat method because of their similar thermal expansion coefficients.

However, these epitaxial crystal substrates
There is no particular problem when the mixed crystal ratio x of Al is as low as about 0.3, but as the mixed crystal ratio x increases to 0.4 or more, distortion appears due to the difference in thermal expansion coefficient between the substrate and the growing crystal, The sled is getting bigger.
If this is significant, the crystal will crack and become unusable. Moreover, the mixed crystal ratio is
A value as high as 0.5 to 0.6 is being demanded.

In addition, devices using GaAlAs single crystal as a substrate are desired, but it is difficult to obtain GaAlAs wafers with a thickness of several hundred μm or more using liquid phase epitaxial growth.
Industrialization was extremely difficult, partly due to poor productivity.

Although the pulling method is considered to be suitable as a method for manufacturing thick wafers, conventional pulling techniques have various problems and have been difficult to put into practical use. For example, when a single crystal is pulled from a GaAlAs melt or a Ga solution containing GaAlAs (a method for pulling a single crystal (Si) from a solution (Al) is disclosed in JP-A-55-50619).
Because the segregation coefficient of Al with respect to GaAs is large, the Al mixed crystal ratio on the seed crystal side is high, and the closer to the rear end of the crystal, the more Al
The mixed crystal ratio becomes low, and wafers with the same Al mixed crystal ratio cannot be obtained from one single crystal ingot. Therefore, it decreases as growth progresses.
GaAlAs to supplement Al (or GaAs and Al)
It is conceivable to supply Al (or GaAl and Al) from the upper part of the melt (or Ga solution) (a method of supplying raw materials to the melt is disclosed in Japanese Patent Publication No. 11675/1983). However, in the case of growth from melt, the amount of Al supplied must be gradually reduced as the GaAlAs melt decreases;
It is extremely difficult to accurately control the amount of Al supplied, and the Al mixed crystal ratio in the longitudinal direction within the obtained ingot becomes non-uniform. In addition, in the case of growth from a Ga solution, whether the GaAs and Al to be supplied are solid or melt, the amount that needs to be replenished according to the growth rate is controlled so that it is continuously and constantly supplied. In reality, it is difficult to
The situation was such that non-uniformity of the Al mixed crystal ratio in the longitudinal direction within the ingot could not be avoided.

[Object of the Invention] The present invention has been made in view of the problems of the prior art described above.
A crystal growth method that can keep the Al mixed crystal ratio in the longitudinal (growth progress) direction of the GaAlAs mixed crystal single crystal constant, and that can easily obtain a large amount of GaAlAs mixed crystal single crystals with a high mixed crystal ratio. The purpose is to provide such equipment.

[Summary of the Invention] The first feature of the present invention is that a temperature-controllable growth Ga solution tank containing a growth Ga solution is connected to a temperature-controllable GaAs melting tank and an Al melting tank, respectively. The Ga solution bath for growth and the GaAs dissolution bath are each filled with the Ga solution for growth, and the Ga solution bath for growth is maintained at a constant temperature. The raw material GaAs and raw material Al put in each are dissolved in the growth Ga solution by heating each of the melting tanks to a predetermined temperature, and are constantly supplied.
After that, the seed crystal is brought into contact with the Ga growth solution in the growth Ga solution bath which has reached the saturated state, and GaAlAs
The purpose is to pull and grow a mixed single crystal.

The second feature is a growth Ga solution tank into which a saturated growth Ga solution containing raw material GaAs and raw material Al is dissolved, a first heater that heats the growth Ga solution tank, and A GaAs dissolving tank and an Al dissolving tank connected to a Ga solution tank to be filled with the growth Ga solution and for respectively accommodating the raw material GaAs and the raw material Al; and the growth Ga solution in the melting tank. A second heater and a third heater respectively heat the respective melting tanks in order to melt and constantly supply the raw material GaAs and the raw material Al.
A seed crystal is brought into contact with the heater and the growth Ga solution in the growth Ga solution tank that has reached a saturated state.
The object of the present invention is to provide a GaAlAs mixed single crystal growth apparatus equipped with a pulling means for pulling up a GaAlAs mixed single crystal.

Here, the method for producing a GaAlAs mixed single crystal from a Ga solution according to the present invention will be explained based on FIG.

Figure 1 is a phase equilibrium diagram of the Ga-Al-As system. At point A in Figure 1, the arsenic concentration at 900℃ is 0.1 mol.
%, Ga _1-x grows when the Al concentration of the solution is 5%
This shows that the Al mixed crystal ratio x of Al _x As is 0.2.

Here, as the arsenic concentration increases at the same temperature, the Al concentration in the Ga solution decreases, and the Al mixed crystal ratio x of the growing Ga _1-x Al _x As increases. .

For example, point B in FIG. 1 indicates that the mixed crystal ratio x of Ga _1-x Al _x As grown when the arsenic concentration is 0.3 mol % and the Al concentration is 4% is 0.35. In this way, compared to the Al mixed crystal ratio in the growing crystal, the solution composition is
The Al/As ratio is small, and the growth process is rate-limited by diffusion of Al in the liquid phase.

This diffusion of Al is generally expressed as (1) and (2) below.

∂N/∂t=D∂ ² N/∂x ² ...(1) D=D _p exp(-E/kT) ...(2) Where, N: concentration, t: time, x: diffusion distance , D: diffusion coefficient, D _p : diffusion coefficient at 0°K, E: energy of diffusion, k: Boltzmann coefficient, T: absolute temperature.

Now, if Al travels a distance L in t seconds by diffusion in the solution, the diffusion coefficient D is expressed as D=L ² /t (3). Rewriting equation (3), L=√...(4), and the distance L traveled by diffusion is the diffusion time t
is proportional to the square root of

Also, assuming that the diffusion energy of the Ga-Al-As system near 1000°C is 5 eV, the ratio of the diffusion coefficients at 900°C and 1000°C is D ₁₂₇₃ /D ₁₁₇₃ = D _p exp (-5/1273k) / D _pexp (−5
/1173k) =exp(5/1173k-5/1273k)≒exp(2.56)≒13.0.

Therefore, in order to increase the diffusion rate of Al, it is sufficient to increase the temperature of the zone where Al is transported, which can significantly increase the Al supply rate.
Crystal growth rate can be increased.

Similarly, the transport rate of GaAs can be changed by changing the temperature.

In this way, GaAs and Al supplied to the Ga solution
Although it is possible to control the amount of GaAs and
The goal is to keep the amount of Al continuously constant. That is,
When supplying GaAs and Al to a Ga solution from above, it is technically extremely difficult to continuously supply a constant amount of GaAs and Al in accordance with the growth rate. Al in
This is because the mixed crystal ratio varies.

Therefore, in the present invention, a Ga solution for growth is introduced.
The GaAs dissolving tank and the Al dissolving tank are connected to the solution tank so that both of these melting tanks are also filled with the Ga solution for growth.
By placing GaAs and Al and setting each tank at a predetermined temperature, GaAs and Al can be continuously and constantly supplied to the Ga solution by utilizing the diffusion rate of GaAs and Al. As a result, the Al mixed crystal ratio in the longitudinal direction of the pulled GaAlAs mixed single crystal can be made uniform.

[Example] Hereinafter, an example of the present invention will be described based on illustrated FIGS. 2 and 3.

FIG. 2 is a schematic diagram showing an embodiment of the mixed crystal growth apparatus of the present invention. In Fig. 2, 1 is a Ga solution tank for growth, 2 is a GaAs dissolution tank, 3 is an Al dissolution tank,
4 is a crystal growth device heater, 5 is a growth Ga solution tank heater, 6 is a GaAs melting tank heater,
7 is an Al melting tank heater, 8 is a growing GaAlAs mixed single crystal, 9 is a raw material Al, 10 is a Ga solution for growth, 1
1 is a GaAs crystal, 12 is a seed crystal, 13 is a gas inlet, 14 is a thermocouple, and the Ga solution tank 1 for growth and GaAs
The melting tank 2 and the Al melting tank 3 are connected as shown in the figure, and both melting tanks 2 and 3 are connected to each other for growth.
An appropriate amount of Ga solution 10 is filled.

In an apparatus having such a configuration, the temperature of the Ga growth solution 10 is set appropriately, and the temperature of the GaAs 11 and
The temperature of the GaAs melting tank heater 6 and the Al melting tank heater 7 is set to a predetermined temperature so that the supply amount of Al9 becomes a predetermined value, and the time point when the concentration of each component in the growth Ga solution 10 reaches an equilibrium state. A Ga _1-x Al _x As mixed single crystal having the target mixed crystal ratio x can be easily obtained by bringing the seed crystal into contact with the crystal and pulling it at an appropriately set pulling rate.

For example, when a GaAs single crystal is used as a seed crystal, the Al mixed crystal ratio in the longitudinal direction of the GaAlAs mixed single crystal is
is as shown in FIG. In Figure 3,
The horizontal axis represents the distance from the seed crystal (seed side) to the rear end (tail side) of the single crystal, and the vertical axis represents the Al mixed crystal ratio: X. Since the seed crystal is GaAs, the Al mixed crystal ratio X is low immediately after the start of growth, but after that the Al mixed crystal ratio The Al mixed crystal ratio increases and becomes even higher than the desired Al mixed crystal ratio. but,
Since the supply amount of Al is constant, the Al mixed crystal ratio gradually decreases (this is the unstable region), and then the change in the mixed crystal ratio becomes stable and constant.

Example 1 A 5 mm x 5 mm x 80 mm GaAs single crystal with a crystal axis in the <100> direction was used as the seed crystal 12, and Ga2
Kg, 600 g of GaAs polycrystal, and 200 g of Al were charged to the growth Ga solution tank 1, GaAs dissolving tank 2, and Al dissolving tank 3, respectively, and while flowing hydrogen gas from the gas inlet 13, the heaters 5 of each tank 1 to 3 were charged. -7, each tank 1-3 is heated, and the temperature immediately below the seed crystal 12 is heated.
900℃, Al melting tank 3 is 1000℃, GaAs melting tank 2 is
The temperature was adjusted to 920℃, and each tank 1 to 3
When the temperature of is stabilized, the seed crystal 12
Ga solution for growth in saturated state by lowering GaAs crystal 10
contact with. Then, the seed crystal 12 is gradually pulled up while observing the growth of the single crystal. At this time, the pulling speed in steady state was about 10 mm/h.

Due to these conditions, a diameter of 50mm and a length of 40mm
We were able to obtain a GaAlAs mixed single crystal.

Incidentally, the Al mixed crystal ratio X at this time was 0.65, and was uniform over the longitudinal direction of the crystal. Furthermore, Al and GaAs existed in sufficient excess in the form of melt and crystals until the end of crystal growth.

Example 2 Seed crystal (GaAs crystal), Ga, GaAs polycrystal, raw material
Al was the same as in Example 1, and the temperature directly below the seed crystal 12 and in the GaAs melting tank 2 was also the same as in Example 1, with only the temperature of the Al melting tank 3 being changed to 960°C. In this case, the crystal growth rate was about half, and a single crystal with a diameter of 40 mm and a length of 45 mm could be obtained.

Note that the Al mixed crystal ratio X at this time was about 0.4, and was uniform over the longitudinal direction of the crystal.

Example 3 The temperature of Al melting tank 3 is the same as that of GaAs melting tank 2 at 920°C.
The procedure was the same as in Example 1 except that the temperature was set at ℃.
Temperature of Ga solution 10 is 900℃, pulling speed is 3
In the case of mm/h, the diameter is 50 mm and the length is 60 mm.
We were able to obtain a single crystal of Furthermore, at this time
The Al mixed crystal ratio X was 0.2 and was uniform over the longitudinal direction of the crystal.

As described above, according to each embodiment, a GaAlAs mixed single crystal with a high Al mixed crystal ratio is formed in the longitudinal direction.
By making the Al mixed crystal ratio uniform, it could be easily produced in large quantities, and since the Ga solution for growth was not consumed, it could be used as many times as needed as long as it did not become contaminated.

[Effects of the Invention] As explained above, according to the GaAlAs mixed single crystal growth method of the present invention and its apparatus, GaAlAs for growth can be
The GaAs dissolving tank and Al dissolving tank connected to the solution tank are also filled with an appropriate amount of Ga solution for growth.
By continuously and constantly supplying the raw materials GaAs and Al to the growth Ga solution by their diffusion, even if the Al mixed crystal ratio is high, the Al mixed crystal ratio remains constant over the longitudinal direction of the crystal. It has the remarkable effect that uniform GaAlAs mixed single crystals can be easily obtained in large quantities.

[Brief explanation of the drawing]

Figure 1 is a phase equilibrium diagram of the Ga-Al-As system, Figure 2 is a schematic configuration diagram showing an embodiment of the crystal growth apparatus of the present invention, and Figure 3 is the Al mixed crystal ratio in the longitudinal direction of the single crystal. FIG. 1: Ga solution tank for growth, 2: GaAs dissolution tank, 3:
Al melting tank, 4: Crystal growth device heater, 5:
Ga solution tank heater for growth, 6: GaAs melting tank heater, 7: Al melting tank heater, 8: Growth
GaAlAs mixed single crystal, 9: Raw material Al, 10: For growth
Ga solution, 11: GaAs polycrystal, 12: seed crystal, 1
3: Gas inlet, 14: Thermocouple.

Claims (1)

[Claims] 1. GaAlAs is grown by bringing a seed crystal into contact with a saturated Ga growth solution in which raw material GaAs and raw material Al are dissolved.
In the method of pulling and growing a mixed single crystal,
A temperature-controllable GaAs dissolving tank and an Al dissolving tank are connected to the temperature-controllable growth Ga solution tank containing the growth Ga solution, so that the growth Ga solution tank and the GaAs dissolving tank are also connected to each other. The growth Ga solution is filled with the growth Ga solution.
The solution baths are maintained at a constant temperature, and the raw material GaAs and the raw material Al, which are respectively put into the growth Ga solution in each of the melting tanks, are heated to a predetermined temperature to cause the growth. for
Ga for growth is dissolved in a Ga solution and supplied constantly, and then the growth Ga in the growth Ga solution bath reaches a saturated state.
A GaAlAs mixed single crystal is pulled and grown by bringing the seed crystal into contact with a solution.
GaAlAs mixed single crystal growth method. 2. A growth Ga solution tank for containing a saturated growth Ga solution in which raw material GaAs and raw material Al are dissolved, and a first heater that heats the growth Ga solution tank;
The growth Ga solution tank is connected to the growth Ga solution tank.
A GaAs dissolving tank and an Al dissolving tank filled with a solution and accommodating the raw material GaAs and the raw material Al, respectively, and the growth tank in the melting tank.
A second heater and a third heater respectively heat the respective melting tanks in order to dissolve and constantly supply the raw material GaAs and the raw material Al in the Ga solution, and Ga for growth
1. A device for growing a GaAlAs mixed single crystal, comprising a pulling means for bringing a seed crystal into contact with a solution to pull up a GaAlAs mixed single crystal.