JP2004203721A - Apparatus and method for growing single crystal - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an apparatus and a method for manufacturing a large size and high quality ZnSe single crystal at a low cost which can be used as a base for an optical device as the large size and high quality ZnSe single crystal cannot be produced in a conventional technique. <P>SOLUTION: In the method for growing the single crystal, a crucible where two kinds of raw materials consisting of a compound are housed is sealed in a quartz ampul in the apparatus for solution growing for a compound single crystal and then, the compound single crystal is grown from the top surface of a liquid without using a seed crystal by a vertical gradient freezing (VGF) method while at least a kind of elements consisting of the compound is supplied as a gas from a second crucible to a liquid raw material in a first crucible. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a solution for growing a compound single crystal, in which at least one of the constituent elements of the compound is supplied as a gas to a raw material liquid placed in a crucible, and vertical gradient freezing is performed without using a seed crystal ( The present invention relates to an apparatus and a growth method for growing the single crystal from the upper surface of a liquid by a VGF method.
[0002]
[Prior art]
ZnSe is expected to be used as a substrate for optical devices because of its physical properties, but a large-sized single crystal substrate with a low crystal defect and high purity that can be applied to devices has not been obtained so far. . This is because Zn and Se in a liquid state in the vicinity of normal pressure have extremely low mutual solubility, so that a mixed melt of Zn and Se cannot be used as a raw material for single crystal growth, This is because growth was difficult.
[0003]
As a conventional method, there is a method of synthesizing ZnSe by a high-pressure melting method, a recrystallization method of a sintered body, a flux method, a CVD method, a simpler gas phase transport method, or the like. In the high-pressure melting method, a single crystal having a diameter of up to about 10 mm is obtained at most, and no large crystal is obtained in the recrystallization method. In the flux method using KCl or the like, contamination due to mixing of the flux is inevitable. A large solid has been obtained as an optical material for infrared rays by a CVD method or a vapor-phase transport method, which is a polycrystalline or amorphous material. A single crystal that can be applied to the above device has not yet been obtained.
[0004]
In general, a II-VI group compound semiconductor such as ZnSe has a smaller generation energy of crystal defects than a III-V group compound semiconductor which is hard to be single-crystallized as compared with a simple semiconductor such as Si. Such crystal defects are likely to occur, which causes polycrystallization. In the liquid phase growth, such crystal defects are mainly generated by a volume change occurring during a phase transformation from a liquid phase to a solid phase at the time of solidification, and a shear stress or a compressive stress generated with the crucible wall. The volume shrinkage that occurs during the process of cooling the solidified crystal from the crystal growth temperature generates internal stress, which further increases the density of crystal defects inside the single crystal.
[0005]
In order to industrially obtain a large single crystal, a melt growth method or a solution growth method is most suitable, and practical use of an apparatus and a method suitable for single crystal growth of various compounds is awaited. In particular, in order to suppress the generation of crystal defects and avoid contamination by a crucible material or the like, it is desirable to use a solution growth that allows single crystal growth at a lower temperature than melt growth.
[0006]
The present inventors have invented a method of growing a high-quality single crystal such as CdTe or CdZnTe by a vertical gradient freezing method, which is known as Japanese Patent No. 3232461. For example, when growing a CdTe single crystal, the present invention uses a CdTe polycrystal as a raw material, and at the same time, fills the inside of a quartz ampoule containing a raw material crucible with Cd vapor at a predetermined pressure, and compensates for Cd lost by dissociation in a molten state. In addition, by optimizing the temperature conditions, a large single crystal can be stably grown. In the case of CdTe single crystal growth, CdTe polycrystal can be used as a raw material, because Cd and Te are uniformly mixed in the raw material melt.
[0007]
On the other hand, as described above, in the case of ZnSe single crystal growth, the mutual solubility of Zn and Se in the liquid phase is extremely low, so that a mixed melt of Zn and Se cannot be used as a raw material. Therefore, in the case of the above-described CdTe single crystal growth, Cd vapor was sufficient to compensate for the dissociation of Cd, but in the case of ZnSe single crystal growth, the single crystal was grown while positively supplying Se. There must be. In order to obtain a high-quality single crystal with few crystal defects, it is useful to grow a single crystal in a floating state on the melt or the upper surface of the solution. If the phase is covered, the subsequent supply of Se is suppressed, and the growth rate of the single crystal is significantly reduced.
[0008]
[Patent Document 1] No. 3232461 [Patent Document 2] No. 2575948 [Patent Document 3] No. 2610319 [Patent Document 4] No. 2585629 [Patent Document 5] No. 2717256 [Patent Document 6] Japanese Patent Publication No. 6-17280 No. [0009]
[Problems to be solved by the invention]
As described above, according to the conventional technique, a large and high-quality ZnSe single crystal that can be used as a substrate for an optical device cannot be obtained. Therefore, it is an object of the present invention to establish an apparatus and a method for manufacturing a large, high-quality ZnSe single crystal at low cost.
[0010]
[Means for Solving the Problems]
Therefore, in the present invention, without using a seed crystal, by using a solution growth method using a device that can start single crystallization from the free surface of the liquid phase, the grown single crystal is suspended on the liquid, The influence of the crucible wall caused by the volume change accompanying the phase transformation during solidification is eliminated, and the generation of crystal defects is suppressed.
[0011]
In order to solidify the single crystal from the upper surface of the liquid, the highest temperature position of the temperature distribution near the outer wall of the quartz ampule corresponding to the first crucible 3 is set to be lower than the crucible, and from the upper end of the crucible. The temperature gradient near the outer wall of the quartz ampoule corresponding to the upper region is made larger than the temperature gradient near the outer wall of the quartz ampule corresponding to the crucible, and the latent heat generated when the solution is crystallized can be quickly removed upward. A structure that can be used.
[0012]
On the other hand, when a compound single crystal is grown by a solution growth method using a material having a low mutual solubility in a molten state, such as Zn and Se, one substance constituting the compound is supplied from outside the solution together with the growth of the crystal. There must be. In the present invention, an element or a compound having a high vapor pressure is put in the second crucible of FIG. 1, heated and evaporated in a lower furnace, and supplied to the solution in the first crucible. At this time, porous carbon is used as the crucible material so that the evaporated substance can pass through the first crucible wall. Further, by placing a heat reflecting plate directly above the first crucible, the temperature of the crucible is maintained at a temperature equal to or higher than the melting point of the solution in the crucible, and the liquid state near the first crucible wall is maintained. The surface is secured as a passage for the above-mentioned evaporated substance.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
In order to solve the above problems, the present inventors have devised an apparatus as shown in FIG. The procedure for growing a single crystal will be described below, taking the case of growing a ZnSe single crystal as an example.
[0014]
First, Zn and Se were weighed, respectively, and a little excess of Se was added to equimolar amounts, and each was placed in a first porous graphite crucible and a second pBN crucible, and placed on the first crucible as shown in FIG. Two crucibles are put in a quartz ampule and sealed in a vacuum with the heat reflecting plate made of pBN placed thereon.
[0015]
Subsequently, the quartz ampoule was loaded into an electric furnace using an upper furnace consisting of four furnaces each capable of independently controlling the temperature and a lower furnace consisting of three furnaces each capable of independently controlling the temperature. In the electric furnace, the temperature near the outer wall of the quartz ampule corresponding to the crucible is 750 ° C. to 900 ° C., and the temperature near the outer wall of the quartz ampule corresponding to the second crucible is 660 ° C. to 700 ° C. in parallel. Heat with. FIG. 3 shows an example of a program for raising the temperature near the outer wall of the quartz ampule corresponding to the first crucible and the second crucible at this time. The vapor pressure of Zn and Se is given by a vapor pressure curve shown in FIG. 4 in each temperature setting region. Maintain at the above temperature for about 10 to 30 hours.
[0016]
Next, the temperature gradient near the outer wall of the quartz ampoule corresponding to the vicinity of the first crucible is set to 0.1 to 10 ° C./cm, and the temperature gradient above the upper end of the crucible is maintained at 0.05 to 0 ° C. The temperature is lowered at a rate of 0.5 ° C./hr, and a ZnSe single crystal is grown from the surface of the first crucible. The density of ZnSe is about 5.6 g / cm ³ and the density of Zn is about 7.1 g / cm ³ . Since the solute has a large excess of Zn, the density of the crystallized ZnSe is lower than the density of the solute, and the ZnSe crystal maintains a stable floating state.
[0017]
Finally, after cooling the inside of the electric furnace to near room temperature, the quartz ampoule is taken out from the electric furnace, divided, a first crucible is collected, and a crystal is collected from the first crucible.
[0018]
【The invention's effect】
Until now, a high-quality ZnSe single crystal applicable to an optical device substrate has not been obtained. However, according to the present invention, a bulky single crystal ZnSe having a large diameter, having few crystal defects such as dislocations, and having little impurity contamination is reduced. Can be obtained at cost. In addition, since the solution growth method is performed at around normal pressure, the apparatus is a simple and low-cost manufacturing technique.
[0019]
[Brief description of the drawings]
FIG. 1 is a schematic sectional view of an apparatus.
FIG. 2 is a perspective view of a first crucible and a heat reflection plate.
FIG. 3 is an example of a heating program of an electric furnace.
FIG. 4 is a vapor pressure curve of Zn and Se.
[Explanation of symbols]
REFERENCE SIGNS LIST 1 heat reflection plate 2 element or compound or mixture with low vapor pressure, compound single crystal 3 first crucible 4 quartz ampule 5 element or compound with high vapor pressure 6 second crucible 7 a, 7 b, 7 c, 7 d Upper furnace 8 a 8b, 8c Lower furnace

Claims (4)

In FIG. 1, an upper furnace consisting of four furnaces 7a, 7b, 7c, and 7d each capable of independently controlling the temperature, and a lower furnace consisting of three furnaces 8a, 8b, and 8c each capable of independently controlling the temperature. In a single crystal growing apparatus using the method, a substance formed of a combination of two of the elements or compounds or the compounds constituting the compound is compared, and the element or compound or the mixture 2 having a low vapor pressure is put in the quartz ampoule 4. The first crucible 3 and the second crucible 6 containing the element or compound 5 having a high vapor pressure are put therein, the quartz ampule is vacuum-sealed, and the quartz ampule is placed in a heating furnace comprising the above-mentioned upper and lower furnaces. Heating to melt the materials in the first crucible and the second crucible, respectively, and heating the second crucible to a predetermined temperature to transfer the material in the second crucible to the first crucible as a gas; And a vertical temperature gradient near the outer wall of the quartz ampoule corresponding to the first crucible is made smaller than a temperature gradient above the upper end of the crucible, so that the temperature in the heating furnace is gradually lowered, An apparatus and method for growing a single crystal, wherein a single crystal of the compound is grown downward from the surface of the solution in the first crucible without using a seed crystal. 2. The apparatus and method for growing a single crystal according to claim 1, wherein a porous carbon material is used for said first crucible. Immediately above the first crucible, there is provided a ring-shaped heat reflecting plate 1 having an outer diameter larger than the outer diameter of the upper end of the crucible and having an opening at the center. And when the diameter of the opening of the first crucible is D, the following equation:
X = d / D
3. The apparatus for growing a single crystal according to claim 1 or 2, wherein X given by is in the range of 0.3 to 0.8, more preferably 0.55 to 0.75. Growth method. 4. The single crystal growth according to claim 1, wherein the single crystal of the compound semiconductor is ZnSe, and a maximum pressure in the quartz ampoule does not exceed 3 atm. Apparatus and growth method.

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