JPH0242800B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method for growing a high-quality compound semiconductor single crystal with a uniform composition and low defect density, and a growth apparatus used therein.

(Summary of the Invention) The present invention cools and liquefies the vaporized crystal raw material in the melt reservoir to form a melt zone in the crystal growth section, and solidifies the melt zone in one direction to promote crystal growth. In the single crystal growth method, compound semiconductor vapor evaporated from an upper melt reservoir section separated from the crystal growth section is transported to the lower crystal growth section and cooled to form a melt zone, and the growing crystal is This is a single crystal growth method that can grow large single crystals with uniform composition and low defect density with high productivity by holding the crystal horizontally on top of the crystal to a uniform thickness and growing the single crystal.

Furthermore, the present invention provides a single crystal growth apparatus in which a vertical electric furnace, a heat-resistant single crystal growth container housed inside the electric furnace, and relative positions between the electric furnace and the container are controlled. The single crystal growth container includes a melt reservoir with a large inner diameter and a crystal with a small diameter extending downward through the center of the melt reservoir. The lower part of the melt reservoir is connected to the crystal growth part, and a nucleation part is provided below the crystal growth part, and the area around the crystal growth part is heated well. This device is capable of growing large single crystals with uniform composition and low defect density with high productivity because they are coated with a conductive material.

(Prior art and problems to be solved by the invention) Conventionally, when growing a mixed single crystal or a single crystal to which impurities have been added, in the melt growth method,
There was a problem in that the composition changed as the crystal grew due to segregation of constituent elements and convection within the melt, making it impossible to grow a single crystal with a uniform composition. For example, PbTe and
In Pb _0.8 Sn _0.2 Te, which is a mixed crystal of SnTe, the composition of the crystal that first crystallizes is Pb _0.87 Sn _0.13 Te.
However, there was a problem in that the Sn concentration in the crystal gradually increased as the crystal growth progressed.
This is because the segregation coefficient of Sn is less than 1 and it is difficult to incorporate into the crystal during solidification, so Sn that has become highly concentrated at the solid-liquid interface is stirred by convection and mixed with the entire remaining melt. This phenomenon occurs because the Sn concentration in the liquid gradually increases as the crystal grows.

On the other hand, in the vapor phase growth method, since there are no problems of segregation or convection, the grown crystals have excellent compositional uniformity and have few defects, but the growth rate is slow and it is not suitable for mass production.

Therefore, a method has been proposed that incorporates the advantages of melt growth and vapor phase growth to grow single crystals with uniform composition and low defect density with high productivity. An example of this is a droplet formation method in which a narrow melt zone is formed by utilizing the change between the gas phase, melt phase, and solid phase, and the melt zone is unidirectionally solidified to grow a single crystal. or horizontal vapor melt solids (Vapor-Melt-
Solid) (VMS) method is known. These methods aim at growing a single crystal with a uniform composition by suppressing convection within the melt zone by narrowing the width of the melt zone. In other words, the magnitude of the driving force of convection becomes smaller as the width l of the melt zone becomes narrower, as expressed by the Grashof number (Gr) shown in the following equation (1), and convection becomes less likely to occur. is used.

Gr=gβΔTl ³ /ν ² ...(1) where g is the gravitational acceleration, β is the coefficient of body expansion of the melt,
ΔT is the temperature difference between both ends of the melt, and ν is the kinematic viscosity coefficient of the melt.

For example, in the case of Pb _1-x Sn _x Te, if the temperature difference ΔT is 10°C, the critical thickness required to suppress convection is approximately 1 cm.
It can be estimated as follows.

FIG. 9 shows the position and shape of the melt zone in the conventional narrow melt zone formation method described above. Figure 9a is the droplet formation method, Figure 9b is the horizontal type.
This is an explanatory diagram of the VMS method. In the diagram, 1 is an ampoule,
2 is the melt in the melt reservoir, 3 is the vapor evaporated from the melt reservoir, 4 is a droplet, 5 is a growing crystal, and 6 is a narrow melt zone. In the droplet formation method shown in FIG. 9a,
The droplet 4 adheres to the bottom of the growing crystal 5 in the form of a droplet due to the surface tension of the melt, making it impossible to form a melt zone of uniform thickness. There was a problem in that a large single crystal could not be grown because it could not be supported by tension alone and the droplets would fall back into the melt reservoir. In addition, in the horizontal VMS method shown in Figure 9b, the melt zone is formed adhering to the side surface of the crystal, so if the thickness of the melt zone exceeds 3 mm, it hangs down toward the bottom of the ampoule 1 and becomes uniform. There was a problem that the uniformity of the composition of the grown crystal deteriorated because the thickness was not uniform. On the other hand, it is also possible to increase the temperature gradient in the crystal growth zone to make the width of the melt zone 3 mm or less, but in this case, the grown crystal will be subjected to large thermal stress, resulting in crystal formation such as small-angle grain boundaries and dislocations. There was a problem that the number of defects increased.

(Means for Solving the Problems) The present invention was proposed to improve the above-mentioned drawbacks, and enables the formation of a melt zone with a uniform thickness even under a low temperature gradient, and with a uniform composition. It is an object of the present invention to provide a single crystal growth method and a growth apparatus that can grow large single crystals with low defect density with high productivity.

The present invention provides a vertical single crystal growth ampoule with a melt reservoir and a crystal growth section, and is configured so that the melt in the melt reservoir does not directly flow into the crystal growth section.
The vapor of the compound semiconductor evaporated from the upper melt reservoir is transported to the crystal growth section provided below, and the vapor is condensed and liquefied in the crystal growth section to form a narrow melt band above the growing crystal. The most important feature is that the melt zone is formed horizontally and has a uniform thickness.

In the conventional technique, a melt zone is formed at the bottom or side of the growing crystal, but the method of the present invention differs in that the melt zone is formed at the top of the growing crystal.

Next, examples of the present invention will be described. It should be noted that the embodiments are merely illustrative, and it goes without saying that various changes and improvements can be made without departing from the spirit of the present invention.

Example 1 FIG. 1 shows an example of a furnace configuration used in the single crystal growth method of the present invention. In the figure, 7 is a vertical electric furnace, 8 and 8' are heaters, and 9
1 is a container for single crystal growth, and 10 is a constant speed movement mechanism for changing the relative position of the electric furnace 7 and the container 9 for single crystal growth.

FIG. 2 is a diagram for explaining an embodiment of the single crystal growth container according to the present invention. The single crystal growth container 9 is made of quartz and has a large diameter melt reservoir 11.
and a crystal growth part 12 with a narrow diameter that extends downward through the center of the melt reservoir 11, and has a structure in which the melt 13 does not flow directly into the crystal growth part 12, that is, the lower part of the melt reservoir 11. The surrounding area and the crystal growth section 12 are connected. The crystal growth section 12 has the same diameter except for the nucleation section 14 at the tip of the ampoule, and has a structure in which no stress is applied to the grown crystal. Further, the crystal growth section 12 is surrounded by a good heat conductive outer tube 15, a good heat conductive fine powder 16, and glass wool 17, which serve to improve temperature uniformity in the radial direction. A hook 1 is attached to the upper end of the single crystal growth container 9.
8 is provided so that the single crystal growth container 9 can be suspended within the core tube of the vertical electric furnace 7 using a wire 19 or the like. Further, the tip of the wire 19 is connected to a constant speed movement mechanism section 10, so that the relative position between the single crystal growth container 9 and the vertical electric furnace can be changed at a constant speed. 20 shows the temperature distribution in the furnace during crystal growth, and 21
is the solidus temperature of the compound semiconductor. Also, 22
is the compound semiconductor vapor evaporated from the melt reservoir 11, 23 is the narrow melt zone formed in the crystal growth region, 24 is the growing crystal, 25 is the moving direction of the single crystal growth container, and 26 is the temperature at the 20 cm position. It is.

The principle of single crystal growth by the method of the present invention _is
A detailed explanation will be given below, taking the case of Sn _x Te crystal growth as an example.

A polycrystalline raw material of Pb _1-x Sn _x Te is placed in a melt reservoir 11 and heated to a high temperature higher than its melting point to form a melt 13. At this time, PbTe and SnTe molecules 22 evaporate from the surface of the melt 13.
A temperature distribution as shown by 20 is formed in the furnace, and there is a temperature gradient from high temperature to low temperature between the melt reservoir section 11 and the crystal growth section 12 of the single crystal growth container 9. do. Therefore, it was vaporized
The vapor 22 composed of PbTe and SnTe molecules is once transported above the melt reservoir, which is at a higher temperature, and then transported to the crystal growth region 12, where the equilibrium vapor pressure is lower. Furthermore, in the crystal growth section 12, a temperature gradient is set so that the tip thereof becomes lower temperature, and the vapor 22 transported here is gradually cooled and liquefied, and becomes a Pb _1-x Sn _x Te melt again. , a melt zone 23 is formed on the growing crystal 24. This melt zone 2
3 is not in contact with the melt 13 in the melt reservoir 11, and one end is in contact with the steam 22, so it is close to an adiabatic state, so the heat capacity can be reduced, and the width can be narrowed to enable efficient cooling. Easy to maintain. In addition, the melt zone 23 is a growing crystal 24
Since it is formed on top and kept horizontal, it can have a uniform thickness without sagging downward. This melt zone 23 is cooled to a solidus temperature of 21 or less by moving the entire single crystal growth container 9 at a constant speed in the direction of the arrow 25, and solidified in one direction from the lower end upward. A crystal 24 grows. The evaporation rate of the steam 22 from the melt 13 and the transport rate of the steam 22 to the crystal growth section 12 are controlled by the furnace temperature distribution 20, and the crystal growth rate is controlled by the speed of movement of the container 9 in the arrow direction 25. to control. In this method, the steam 22 is
The thickness of the melt zone 23 is adjusted so that the speed at which the melt zone 23 is increased in thickness by being transported to the molten zone 2 and liquefied is the same as the rate at which the melt zone 23 is solidified and its thickness is decreased. It is important to adjust so that it always remains constant. Figure 3 shows solidus temperatures 21 and 20.
The relationship between the temperature difference from the temperature 26 at the cm position and the speed at which the melt zone is formed is shown. Since the rate at which a melt zone is formed at a temperature difference of 100° C. is 0.4 mm/h, the moving speed of the container was adjusted accordingly. The speed at which the melt zone was formed was adjustable between 0.1 mm/h and 2 mm/h.

FIG. 4 shows the Sn concentration distribution in the growth axis direction of the single crystal grown by the method of the present invention as compared with that of the conventional Bridgeman method.
In the figure, the solid line indicates the case grown by the method of the present invention,
The broken line shows the case grown by the conventional method. In both cases, the temperature gradient near the solidus temperature was 15° C./cm, and the solidification rate was 0.5 mm/h. From Figure 4, when grown by the method of the present invention, for a crystal with a length of 10 cm,
The Sn concentration is constant at about 19 at.% in the length range from 2 cm to 8 cm, and a very long single crystal with a uniform composition region can be obtained, whereas in the conventional method, the Sn concentration is 19 at.%.
It can be seen that the area is less than 0.5 cm. This result indicates that the melt has been vaporized and transported.
PbTe and SnTe have the same composition as the original melt (Pb _0.8 Sn _0.2
This shows that the crystal 24 was grown in a state in which a narrow and uniformly thick melt zone 23 of Te) was formed and convection within the melt zone 23 was suppressed. The effectiveness of the construct is clear.

FIG. 5 is a schematic diagram of an X-ray topographic image showing the degree of occurrence of low-angle grain boundaries in the grown single crystal. When grown using the conventional method, the diameter is 1 mm as shown in Figure 5 a.
While there are many low-angle grain boundaries with a size of ~2 mm, when grown by the method of the present invention, as shown in FIG. 5b, there are no low-angle grain boundaries at all.

Further, in growing a single crystal by the method of the present invention, a composition of the crystal raw material in the range of -0.2y0.01 in the expression (Pb _0.8 Sn _0.2 ) _1-y Te _1+y was particularly suitable. This means that even if the composition of the crystal raw material deviates from the stoichiometric ratio, the partial pressures of PbTe and SnTe are
Because it is more than an order of magnitude higher than the Pb partial pressure and Sn partial pressure,
This is because the composition of the vaporized vapor is approximately equal to the stoichiometric composition.

Example 2 An example of growing a single crystal of a quaternary compound semiconductor of Pb _0.8 Sn _0.2 Te _0.7 Se _0.3 is described below.

Figure 6 shows the temperature gradient of the electric furnace at 25℃/cm and the solidification rate.
FIG. 3 is a diagram showing the dependence of the Sn concentration on the growth axis direction in a quaternary mixed crystal grown at 0.5 mm/h. In this case as well, for a crystal with a length of 10 cm, the Sn concentration is constant in the range from about 1.5 cm to about 9 cm in length, and a very long high-quality single crystal with a uniform composition region can be grown. I understand.

Next, other examples of the single crystal growth container used in the present invention will be described.

FIG. 7 is a sectional view showing a second embodiment of the single crystal growth container. In the figures, the same reference numerals as those mentioned above indicate the same or equivalent parts. A seed crystal holder 27 is provided at the tip of the crystal growth section 12 in this container, and a seed crystal 28 can be used to grow a single crystal with a controlled growth direction.

FIG. 8 is a sectional view showing still another embodiment of the single crystal growth container. A crucible 29 made of a good thermal conductor is installed inside the container in the crystal growth section 12, and the temperature distribution in the radial direction of the crystal growth section 12 is made uniform, allowing single crystal growth with low dislocation density and no small-angle grain boundaries. can be done. This has the advantage that boron nitride and graphite, which are good thermal conductors that oxidize or burn in air, can be used as the crucible material.

Note that the single crystal growth container used in the present invention is
If you make the electric furnace larger, you can make it as thick as you like. In addition, the length of the melt reservoir and the length of the crystal growth region can be changed arbitrarily, but especially when the length of the melt reservoir and the length of the crystal growth region are 3:1 to 1:1. Good results were obtained.

Furthermore, when growing a single crystal using the method of the present invention, the temperature gradient near the solidus temperature of 21 is 40°C/cm.
In the following cases, the occurrence of low-angle grain boundaries was suppressed, and high-quality single crystals could be grown.

The effects of the present invention are not limited to the growth of - group compound semiconductor single crystals as described in the examples, but also for alloys and compound semiconductors consisting of two or more elements, in which the constituent components are transported to the crystal growth part in the gas phase. However, it is effective for all systems in which a melt of an alloy or compound semiconductor can be formed without using a solvent in the crystal growth region.

(Effects of the Invention) As explained above, the single crystal growth method and the growth apparatus of the present invention have the following advantages.

(b) Since the vertical furnace configuration is used to form the melt zone on top of the growing crystal, the melt zone remains horizontal without sagging even if the temperature gradient of the furnace is reduced to reduce the occurrence of thermal stress. This makes it possible to easily form a melt zone with a uniform thickness and with good controllability, and to grow single crystals with excellent compositional uniformity and low defect density with few small-angle grain boundaries and dislocations. can.

(b) Since vaporization is performed at a high temperature above the melting point, crystals can be grown at a rate about one order of magnitude faster than in the case of simple vapor phase growth, and large single crystals can be grown with high productivity.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of an embodiment of the apparatus configuration used in the single crystal growth method of the present invention, Fig. 2 is a sectional view of the first embodiment of the single crystal growth container of the invention, and Fig. 3 is a temperature A line drawing showing the relationship between the difference and the speed at which a melt zone is formed. Figure 4 shows the Sn concentration distribution in the growth axis direction of a Pb _1-x Sn _x Te crystal grown by the method of the present invention compared to that grown by the conventional Bridgeman method. Figure 5 is a schematic diagram of an X-ray topographic image showing the degree of occurrence of low-angle grain boundaries in the crystal, Figure 6 is a line drawing compared to the case of Pb _1-x.
Line drawings to explain the dependence of Sn concentration on the growth axis direction in Sn _x Te _1-y Se _y system mixed crystals, Figure 7 is a cross-sectional view of the second embodiment of the single crystal growth container, and Figure 8 is FIG. 9 is a cross-sectional view for explaining the third embodiment of the single crystal growth container, and FIG. 9 is a view for explaining the conventional method for forming a narrow melt zone. 1...Ampoule, 2...Melt reservoir, 3...
...Steam evaporated from the melt reservoir, 4...Droplets, 5
...Growing crystal, 6...Narrow melt zone, 7...Vertical electric furnace, 8, 8'...Heater, 9...Single crystal growth container, 10...Constant speed movement mechanism section, 11... Melt reservoir part, 12... Crystal growth part, 13... Melt liquid, 14
...Nucleation part, 15...Good thermal conductivity outer tube, 16...
...Good thermal conductivity fine powder, 17...Glass wool, 1
8...Hook, 19...Wire, 20...Furnace temperature distribution, 21...Solidus temperature of compound semiconductor,
22... Compound semiconductor vapor, 23... Narrow melt zone, 24... Growing crystal, 25... Container moving direction,
26... Temperature at 20 cm position, 27... Seed crystal holder, 28... Seed crystal, 29... Good thermal conductor crucible. [References] (1) Solidification of metals (co-translated by Okamoto and Suzuki, Maruzen, 1980)
P134 (2) SGParker; J.Electron.Mater, 5 , 479
(1976) (3) D.Mateika; J.Crystal.Growth. 9 , 249
(1971) (4) Patent application 1986-63876

Claims (1)

[Claims] 1. A unit for forming a melt zone by cooling and liquefying the vapor of the crystal raw material vaporized in the melt reservoir section in the crystal growth section, and unidirectionally solidifying the melt zone for crystal growth. In the crystal growth method, the compound semiconductor vapor evaporated from the upper melt reservoir section that is separated from the crystal growth section is once transported to the upper part of the melt reservoir section, which is at a higher temperature than the melt reservoir section, and then transported further below. A method for growing a compound semiconductor single crystal, which comprises transporting the melt to a crystal growth section and cooling it to form a melt zone, and holding the melt zone horizontally above the growing crystal to a uniform thickness to grow the single crystal. 2. A vertical electric furnace, a heat-resistant single crystal growth container housed inside the electric furnace, and a constant speed movement mechanism for changing the relative position between the electric furnace and the container. The single crystal growth container has a melt reservoir with a large inner diameter and a crystal growth section with a small diameter extending downward through the center of the melt reservoir, and a melt reservoir. The periphery of the lower part of the crystal growth part is connected to the crystal growth part, and a crystal nucleation part is provided below the crystal growth part, and the periphery of the crystal growth part is covered with a material having good thermal conductivity. A single crystal growth device characterized by: