WO2016046983A1

WO2016046983A1 - Method of crystal growth

Info

Publication number: WO2016046983A1
Application number: PCT/JP2014/075717
Authority: WO
Inventors: 崇章石津; 信也小南; 上野　雄一郎; 喬之神田
Original assignee: 株式会社日立製作所
Priority date: 2014-09-26
Filing date: 2014-09-26
Publication date: 2016-03-31

Abstract

The present invention addresses the problem of providing a highly efficient method of crystal growth which highly purifies a semiconductor crystal material and with which high-purity high-quality crystals can be isolated. A method of crystal growth comprises the following steps performed in the following order in the same container: a refining step (S1) of placing a crystalline material (1) in a tubular container (2) that is closed at one end and substantially leveling the tubular container (2), then sequentially moving a portion of the crystalline material (1) placed in the tubular container (2) and melted into a belt shape from one end to the other end in a substantially horizontal direction to segregate impurities contained in the crystalline material (1) to the other end of the crystalline material (1); a separating step (S2) of partially melting the crystalline material (1) in which the impurities have been segregated to separate the same into a refined material (11) with less impurities and an impure material (12) with more impurities; and a crystal growth step (3) of cooling the refined material (11) after melting the same with the impure material separated in a solidified state and growing crystals in the container (2) positioned substantially vertical.

Description

Crystal growth method

The present invention relates to a large and high purity crystal growth method.

Recently, in the development of medical devices using radiation, semiconductor detectors tend to be employed as radiation detectors. The semiconductor detector can convert incident radiation directly into an electrical signal. For this reason, by adopting the semiconductor detector, the radiation detector and the medical device can be miniaturized. Further, the semiconductor detector has a feature that the energy of radiation (for example, gamma rays) can be accurately measured.

In semiconductor detectors, when radiation is incident on a semiconductor crystal placed in an electric field generated by applying a high voltage, charge carriers (electrons and holes) generated by the interaction between the radiation and the semiconductor crystal are generated by the electric field. Based on the principle of movement, the intensity of radiation is converted into an electrical signal (current, charge, etc.) and extracted.

Charge carriers generated in the semiconductor crystal are captured by impurities, crystal defects, and crystal interfaces present in the semiconductor crystal, or recombination is promoted. For this reason, the higher the impurity concentration in the semiconductor crystal and the higher the crystal defect density, the lower the charge carrier mobility. Further, the higher the impurity concentration in the semiconductor crystal and the higher the crystal defect density, the shorter the average life of the charge carriers.

Therefore, the purity of the semiconductor crystal and the quality of the semiconductor crystal are very important for the semiconductor crystal used in the semiconductor detector.

As a method for purifying compound semiconductor crystals, which are semiconductor crystals, and a method for growing a single crystal, a group III-V compound is housed in a crucible, a group III element is arranged on the top, and a liquid seal is formed on the top. The crucible is sealed by arranging a material, and then the Group III element is melted by a heater, and the Group III-V compound is sequentially melted by the boundary surface where both the Group III elements are melted by melting the Group III element. And moving the melting zone below the group III-V compound and precipitating crystals of the group III-V compound to float above the melting zone. In this state, the crucible is placed in the crucible. A method of growing a single crystal of the III-V compound semiconductor by arranging a seed crystal and bringing it into contact with the melting zone is disclosed (refer to the claims of Patent Document 1).

In addition, after purifying to a certain level of purity using a horizontal belt melting refiner, the rod-shaped body obtained is set again in a vertical belt melting refiner and purified again using a vertical belt melting device. There is known a method of performing a desired level of high purity by performing the above. When performing the zone melting purification, a zone melting purification apparatus that can be used for both vertical and horizontal types, can reduce the purification cost by zone melting purification, and is easy to maintain is disclosed. . Specifically, a support portion of a rod-shaped body is formed on one end side and the other end side of the base, and a protective tube surrounding the rod-shaped body supported by the support portion is provided between the both support portions. A high-frequency transformer is provided on the base so as to be movable in the longitudinal direction of the protective tube, and an induction heating coil that moves along the protective tube is connected to the high-frequency transformer, so that the high-frequency transformer is moved to the base. There is disclosed a belt melting and purifying apparatus characterized in that, while a mechanism is provided, the base is provided so as to be movable up and down along a vertical plane including a protective tube (Patent Document 2 claims) reference).

JP-A-1-103984 JP-A-2-225391

However, in the method described in Patent Document 1, when collecting impurities in the vertical direction, it is necessary to melt the central portion in a state where the upper and lower sides are solid during purification, and therefore, the crystal layer easily changes. There is a problem. In addition, the method described in Patent Document 1 has a problem that stress due to thermal expansion during melting is applied to the container.

The apparatus described in Patent Document 2 is an apparatus that performs rough purification that collects impurities in the horizontal direction of the left and right and main purification that collects impurities in the vertical and vertical directions, and requires a cooling time for the purified product to reverse the purification direction. Therefore, there is a problem that work efficiency is lowered. In addition, since the apparatus described in Patent Document 2 is an apparatus that once removes a crude product after purification in the left-right horizontal direction, and once again grips the crude product in the vertical direction and performs purification in the vertical direction. There is a problem that work efficiency decreases. Furthermore, since the apparatus described in Patent Document 2 performs purification in the vertical direction, there is also a problem that the crystal layer changes easily as in the method described in Patent Document 1. In addition, the apparatus described in Patent Document 2 is difficult to use depending on the type of the purified product because the crude purified product is once taken out. The device described in Patent Document 2 is not a device that takes into account the isolation of a purified portion having a high purity because there is no description regarding the removal of the purified product.

The present invention solves the above-described conventional problems, and provides a highly efficient crystal growth method capable of isolating high-purity and high-quality crystals while increasing the purity of a semiconductor crystal raw material. This is the issue.

In the present invention, the crystalline raw material is accommodated in a tubular container with one end closed, and after the tubular container is substantially horizontal, the crystalline raw material accommodated in the tubular container is melted in a strip shape from one end to the other end. Sequentially moving the part in a substantially horizontal direction, the purification step of segregating impurities contained in the crystalline raw material to the other end of the crystalline raw material, partially melting the crystalline raw material segregated impurities, In the separation step for separating the purified raw material with few impurities and the impure raw material with many impurities, and in the container in a substantially vertical direction, the purified raw material is in a molten state while the impure raw material is separated in a solidified state. A crystal growth step of growing crystals by post-cooling is performed in the same container in this order.

According to the present invention, it is possible to provide a high-efficiency crystal growth method in which a semiconductor crystal raw material is highly purified and can be isolated as a high-purity and high-quality crystal.

It is a flowchart of the crystal growth method of 1st Embodiment of this invention. It is a figure which shows the outline of the refinement | purification process in 1st Embodiment of this invention. It is a figure which shows the outline of the isolation | separation process in 1st Embodiment of this invention. It is a figure which shows the outline after completion | finish of the isolation | separation process in 1st Embodiment of this invention. It is a figure which shows the outline of the crystal growth process in 1st Embodiment of this invention. It is a figure which shows the outline of the refinement | purification process in 2nd Embodiment of this invention. It is a figure which shows the outline of the isolation | separation process in 2nd Embodiment of this invention. It is a figure which shows the outline of the refinement | purification process in 3rd Embodiment of this invention. It is a figure which shows the outline of the isolation | separation process in 3rd Embodiment of this invention. It is a figure which shows the outline of the refinement | purification process in the modification of this invention.

Hereinafter, the present invention will be described in detail with reference to the drawings as appropriate for each embodiment.

<First Embodiment>
The first embodiment will be described in detail with reference to the drawings (FIGS. 1 to 5) as appropriate. As shown in FIG. 1, the first embodiment includes a purification step S1, a separation step S2, and a crystal growth step S3, which are performed in this order. In the present embodiment, as an example, a case will be described in which a growing crystal is a thallium bromide (TlBr) crystal.

FIG. 2 shows an outline of the purification step S1 of thallium bromide 1 (compound semiconductor). As shown in FIG. 2, the purification step S1 of thallium bromide 1 uses thallium bromide 1 (compound semiconductor) using an elongated cylindrical container 2 and a heater 3 arranged so as to surround the container 2. This is a step of performing purification (purification).

[container]
For example, as shown in FIG. 2, the container 2 has a structure in which one end of a cylindrical quartz glass tube having both ends opened is sealed and a quartz glass tube 22 having a diameter smaller than that of the quartz glass tube is connected to the other end. The quartz glass tube 22 connected to the other end serves as a raw material charging port, and also serves as a connecting portion with an internal pressure adjusting substance supply device (not shown) described later. Since the configuration of the container 2 is a simple cylindrical shape, the container 2 can be easily downsized. Moreover, when the shape of the container 2 is an elongated shape, it becomes easy to spread thinly in the container 2 in which the raw material is stored. The sealing of the quartz glass tube is, for example, closing the quartz glass tube while melting it with a gas burner, and removing the excess quartz glass tube. The container 2 is held by a container holding device 5.

A raw material fall prevention unit 23 is provided inside the container 2. The raw material fall prevention unit 23 may be formed by bonding another quartz glass to the inner peripheral surface of the quartz glass tube, or may be formed by deforming a part of the quartz glass tube. For example, the raw material fall prevention unit 23 has a height of 1/8 or less of the diameter of the container 2 on the inner peripheral surface of the container 2 and is formed in a belt shape along the circumferential direction. By providing the raw material fall prevention unit 23 in the container 2, the thallium bromide 1 (raw material) is prevented from dropping even when the orientation of the container 2 is changed (details will be described later).

[Heating device]
The heater 3 is a heating element that generates heat when energized, for example. The heater 3 is installed in the heater moving device 4. The heater moving device 4 includes a mechanism structure capable of moving the heater 3 along the axial direction (lateral direction in FIG. 2) of the cylindrical container 2, and the heater 3 is positioned at any position in the axial direction of the cylindrical container 2. At rest. The heater moving device 4 may be disposed on the container holding device 5.

Further, an auxiliary heater 32 is disposed on the upper side of the container 2. The auxiliary heater 32 is a heating element that generates heat when energized, for example. The auxiliary heater 32 raises the temperature of the entire container 2. In the present embodiment, the auxiliary heater 32 is disposed only on the upper portion, but may be disposed so as to cover the entire container 2. The heating output per unit area of the auxiliary heater 32 is smaller than that of the heater 3.

Furthermore, the auxiliary heater 32 may be capable of heating only a part of the container 2. By using the heater 3 and the auxiliary heater 32 at the same time, only a part of the thallium bromide 1 in the container 2 can be melted.

[Container holding device]
The container holding device 5 is a device that holds a container.
The container holding device 5 is preferably an apparatus that can rotate at least the direction of the container 2 from a substantially horizontal direction to a substantially vertical direction (around 90 °) while holding the container.
Examples of the container holding device 5 include a clamp that is rotatably attached to a stand.

[Compound semiconductor]
First of all, the conditions required for compound semiconductors used in semiconductor detectors, which are radiation detectors, are such that the density of the compound is such that it interacts with radiation (eg gamma rays) to generate charge carriers. It is large and the atomic number of the atoms constituting the compound is large.

When the semiconductor detector is used at room temperature (20 ° C. to 25 ° C.), it is preferable that the band gap of the molecular orbitals is large in order to reduce the influence of heat-induced carrier induction. For example, silicon that is not a compound semiconductor but has a band gap of 1.11 eV can be used as it is for a semiconductor detector at room temperature. However, germanium, which has a smaller band gap than silicon and has a band gap of 0.67 eV, needs to be cooled when used in a semiconductor detector at room temperature.

Examples of compound semiconductors that satisfy these conditions include cadmium telluride (CdTe), cadmium zinc telluride (CdZnTe), gallium arsenide (GaAs), mercury iodide (HgI ₂ ), thallium bromide (TlBr), and the like. Many of the compound semiconductors listed here are composed of elements that require handling, and the compound itself requires handling. In addition, the compound semiconductors listed here have characteristics such that a part of them vaporizes and sublimes during crystal growth because of a high vapor pressure.

[Internal pressure regulator]
The internal pressure adjusting substance is a substance that is supplied into the container 2 for the purpose of suppressing evaporation and sublimation of the compound semiconductor having a high vapor pressure through the purification step S1, the separation step S2, and the crystal growth step S3.

The internal pressure adjusting substance is preferably a substance that does not react with the substance to be purified, a substance composed of an element constituting the substance to be refined, a substance containing an element constituting the substance to be refined, or the like. The internal pressure adjusting substance is preferably a substance made of an element constituting the substance to be purified because it does not become an impurity even when incorporated into the substance to be purified.
The internal pressure adjusting substance may be in the state of gas, liquid, or solid under normal temperature and pressure as long as it satisfies these conditions. Among the substances satisfying these conditions, the internal pressure adjusting substance is preferably a gas at normal temperature that can be introduced into the container 2 as it is or a substance having a high vapor pressure.

An example of a gas that does not react with the substance to be purified is a rare gas. When purifying thallium bromide, for example, a rare gas, hydrogen bromide, bromine or the like can be used as the internal pressure adjusting substance, and bromine is preferred among them.

[Purification process]
The purification step is a step of purifying the raw material by segregating impurities in the raw material of the compound semiconductor crystal.

(Preparation)
In the refining step S <b> 1, first, thallium bromide, which is a raw material for crystal of a compound semiconductor and is a target for purification (purification), is charged into the container 2 through the quartz glass tube 22. The amount of thallium bromide charged into the container 2 is an amount that is less than half the height of the container 2 placed substantially horizontally, and is about ¼ from the bottom of the cylindrical portion of the container 2 placed substantially horizontally. An amount is preferred (see FIG. 2).

Next, the auxiliary heater 32 heats the upper surface of the container 2 to make the temperature of the upper surface of the container 2 higher than the temperature of the lower surface of the container 2. Thereby, even if it is thallium bromide 1 (substance to be purified) having a high vapor pressure, thallium bromide crystals inside the upper surface of the container 2 generated by cooling the gas of thallium bromide on the upper surface of the container 2. Can be avoided. Further, impurities (for example, thallium iodide (TlI)) present in the thallium bromide 1 are prevented from adhering to the inside of the upper surface of the container 2. Further, impurities are prevented from adhering to the surface of thallium bromide 1 after purification.

And the quartz glass tube 22 of the container 2 is connected to the supply apparatus of an internal pressure adjusting substance. Subsequently, the internal pressure adjusting substance is supplied into the container 2 so that the inside of the container 2 is filled with the internal pressure adjusting substance.
While the thallium bromide 1 is purified in the purification step S1, the suction state and the supply of the internal pressure adjusting substance are repeated to maintain the purity of the internal pressure adjusting substance in the container 2. The purity of the internal pressure adjusting substance may be maintained by continuing to supply the internal pressure adjusting substance into the container 2.

By repeating the suction in the container 2 and the supply of the internal pressure adjusting substance into the container 2, impurities having a high vapor pressure that are easily evaporated, sublimable impurities, evaporation, and sublimated thallium bromide are adjusted to the internal pressure. The substance is transported out of the container 2 through the quartz glass tube 22.
The internal pressure of the container 2, the amount of the internal pressure adjusting substance, etc. are determined based on the shape and size of the container 2, the amount of thallium bromide 1 and the like.

The structure and type of the supply device for the internal pressure adjusting substance are not limited as long as the internal pressure adjusting substance can be supplied into the container 2 at a predetermined pressure and a predetermined amount. Examples of the supply device for the internal pressure adjusting substance include a cylinder filled with the internal pressure adjusting substance and a gas generator for generating a gas of the internal pressure adjusting substance. Examples of the gas generator include a device that vaporizes a liquid or solid internal pressure adjusting substance under normal temperature and normal pressure by means such as heating, bubbling, decompression, and ultrasonic irradiation.

(Purification)
First, the heater 3 is moved by the heater moving device 4 to the side opposite to the quartz glass tube 22 connected to one end of the container 2 (right side toward the container 2 in FIG. 2). The heater 3 is energized, and the heater 3 heats the portion of the thallium bromide 1 in the container 2 facing the heater 3, so that only the portion of the container 2 facing the heater 3 of the thallium bromide 1 is strip-shaped. Melt to

Next, the heater moving device 4 causes the heated heater 3 to move toward the quartz glass tube 22 connected to one end of the container 2 (on the left side in FIG. 2 toward the container 2). It moves slowly while maintaining a belt-like melting state facing the heater 3. The thallium bromide 1 opposite to the newly heated heater 3 is heated to a molten state.

On the other hand, in the portion of thallium bromide 1 that is no longer opposed to the heated heater 3 and is no longer heated (on the right side of the heater 3 in FIG. 2), the thallium bromide 1 is gradually cooled, so that the thallium bromide 1 gradually increases. It solidifies and becomes a crystal. That is, the band-shaped melted portion of thallium bromide 1 also moves from the sealing 21 side of the container 2 to the quartz glass tube 22 side (from the right side to the left side in FIG. 2) (see FIG. 2).

When thallium bromide 1 is heated and melted, impurities in thallium bromide 1 are released into the liquid layer, and when thallium bromide 1 is cooled and crystallized (solidifies), the impurities remain in the liquid layer. For this reason, the purity of the recrystallized (re-solidified) portion of thallium bromide 1 is improved. The moving speed of the heater 3 is, for example, 1 mm / h or more and 30 mm / h or less. In the case of thallium bromide, when the moving speed of the heater 3 exceeds 30 mm / h, the heating rate and the cooling rate are high, so that the crystal to grow does not become a single crystal.

When the heater 3 reaches the quartz glass tube 22 side of the container 2 (left side of the container in FIG. 2), impurities in the thallium bromide 1 gather on the quartz glass tube 22 side (left side of FIG. 2) of the thallium bromide 1. It is done. For this reason, the thallium bromide 1 has a high purity on the side of the sealing 21 and a low purity on the side of the quartz glass tube 22. The heater 3 in the heated state is moved a plurality of times in one direction from the sealing 21 side of the thallium bromide 1 to the quartz glass tube 22 side, and the thallium bromide 1 is melted and recrystallized repeatedly, so that the odor The purity of thallium oxide is further improved.

Specifically, the heater 3 reaching the quartz glass tube 22 side moves to the sealing 21 side (right side in FIG. 2) of the container 2 without melting the thallium bromide 1 in the container 2. Next, the heater 3 in a heated state moves slowly from the sealing 21 side of the container 2 to the quartz glass tube 22 side, and bromides in one direction from the sealing 21 side of the container 2 to the quartz glass tube 22 side. Thallium 1 is melted and crystallized (solidified) again.
By repeating this operation a plurality of times, impurities that are difficult to diffuse into the liquid layer also move on the glass tube 22 side of the thallium bromide 1, and the purity of the thallium bromide 1 container 2 on the sealing 21 side is further improved.

(Sealing work)
The sealing operation is an operation that prevents evaporation and sublimation of the raw material during or after the purification step S1, and prevents impurities from being mixed into the purified raw material.

After the purification of thallium bromide 1 is completed, for example, the quartz glass tube 22 of the container 2 is sealed with a gas burner, and the container 2 is sealed. The container 2 may be sealed using a sealing material.
The sealing of the container 2 may be performed at the time when the volatile impurities are sufficiently reduced, even before (endway) the purification step S1.

[Separation process]
The separation step S2 is a step of separating the purified raw material, which is a purified portion in which impurities in the compound semiconductor crystal raw material are reduced by the purification step, and the impure raw material, which is a portion in which impurities are segregated to increase impurities. .

FIG. 3 shows an outline of the separation step S2 in this embodiment, and shows a state in which the thallium bromide 1 is separated in the container 2. As shown in FIG. 3, the separation step S <b> 2 is performed using a container 2 held in the vertical direction and a heater 3 that can move along the surface of the container 2. FIG. 4 shows an outline after the separation step S2 in the present embodiment. As shown in FIG. 4, at the end of the separation step S <b> 2, the thallium bromide 1 is separated above and below the container 2.

First, thallium bromide 1 is kept in the same container 2 without being taken out from the container 2 even after the purification step S1 ends. Thereby, evaporation and sublimation of thallium bromide 1 are prevented, and purification efficiency is improved. In addition, work efficiency is improved because the work is performed in the same container.

Next, the direction of the container 2 is changed by adjusting the container holding device 5 so that the sealing 21 side of the container 2 faces down. In this state, the purity of the thallium bromide 1 in the container 2 decreases from the bottom to the top.
Then, the boundary between the refined raw material where the impurities of thallium bromide 1 are reduced and the impure raw material where the impurities are increased by segregating impurities, for example, about 5 minutes from the top of thallium bromide 1 The heater 3 is arranged at the position 1.

The purity of the purified raw material is preferably as high as possible in consideration of obtaining a (single) crystal having a high purity in the crystal growth step S3. The purity of the purified raw material (purified thallium bromide 11) is preferably 99% by mass or more, for example. However, the purity of the purified raw material may be appropriately determined as necessary.

Furthermore, the refined raw material is dissolved while the thallium bromide 1 is dissolved at the boundary by moving the heater 3 heated on the surface of the container 2 from the boundary toward the lower side of the container 2 (sealing 21 side). And impure raw materials are separated. At the same time, the heater 3 moves the refined thallium bromide 11 having a high purity below the boundary to the lower part of the container 2 (see FIG. 3).

As a result, solidified impure thallium bromide 12 having segregated impurities is present in the upper part of the container 2 (on the quartz glass tube 22 side), and purified purified thallium bromide 11 is present in the lower part of the container 2. (See FIG. 4).
The separation position (boundary) of thallium bromide 1 may be calculated from the segregation rate of impurities, or may be determined by measuring the purity of thallium bromide by conducting a preliminary experiment.

The separation of thallium bromide 1 may be performed by a method in which the heater 3 heats and dissolves the thallium bromide 1 at the boundary, moves the separated thallium bromide 11 to the lower part of the container 2 after separation. .
Since the entire amount of the purified thallium bromide 11 is dissolved in the crystal growth step S3, the heater 3 only needs to move from the boundary to the middle of the lower side of the container 2 (side of the sealing 21).

After the heater 3 moves from the lower side of the container 2 (sealing 21 side) and dissolves a high-purity portion of the purified thallium bromide 11 (for example, about half of thallium bromide 1), The remaining thallium bromide 1 may be heated, dissolved, separated and moved at the boundary.
The impure thallium bromide 12 is prevented from being peeled off from the wall surface of the container 2 by the raw material fall prevention unit 23.

Subsequently, the thallium bromide is not taken out from the container 2 and is recrystallized in the subsequent crystal growth step S3 while the separated thallium bromide (purified thallium bromide 11) is contained in the container 2.

In the separation step S2, by separating the purified thallium bromide 11 having a small amount of impurities from the thallium bromide 1, the impure thallium bromide 12 having a large amount of impurities can be easily maintained in a solidified state. In the present embodiment, since the separation step S2 is performed, thallium bromide is easily isolated from thallium bromide 1 in the form of high-purity crystals and is easily obtained.

[Crystal growth equipment]
FIG. 5 shows a container 2 containing thallium bromide 1 and a crystal growth apparatus 6 used in this embodiment. The crystal growth apparatus 6 includes at least a heat insulating material 61, a heater 62, and an elevating mechanism 63.
The crystal growth apparatus 6 may be attachable to the container 2. The heat insulating material 61 is disposed on the outer periphery of the heater 62. The heat insulating material 61 reduces the electric power used by the heater 62 when keeping the container 2 at a high temperature, and at the same time, alleviates changes such as temperature changes of the thallium bromide 1 (raw material) sealed in the container 2 due to changes in the external environment. . The heater 62 is disposed so as to surround the outer periphery of the container 2 in which the thallium bromide 1 is accommodated. The elevating mechanism 63 holds the container 2 from the lower part (sealing 21 side). Further, the elevating mechanism 63 makes it possible to adjust the height position of the container 2 and appropriately perform heating by the heater 62. Any one of the heat insulating material 61, the heater 62, and the lifting mechanism 63 can be used as long as the purpose is achieved.

[Crystal growth process]
The crystal growth step S3 is a step of growing a single crystal from the purified raw material of the compound semiconductor crystal separated in the separation step S2.

First, the purified thallium bromide 1 is not taken out from the container 2 after the separation step S2 and is kept in the same container 2. Thereby, evaporation and sublimation of thallium bromide 1 are prevented, and purification efficiency is improved. In addition, work efficiency is improved because the work is performed in the same container.

Next, the heater 62 heats and melts the purified thallium bromide 1 at the bottom of the container 2 (on the side of the seal 21). The temperature of thallium bromide 1 melted by the heating of the heater 62 is preferably slightly higher than the melting point of thallium bromide 1.

Then, by lowering the temperature of the molten thallium bromide 1 from the thallium bromide 1 existing in the lower part of the container 2, the thallium bromide 1 is gradually crystallized from below. Specifically, the lifting mechanism 63 that holds the container 2 is adjusted, the position of the container 2 is lowered, and the lower part of the container 2 is separated from the heater 62. Thereby, the temperature of the thallium bromide 1 melted from the lower side of the container 2 is lowered. At this time, in order to obtain a single crystal from thallium bromide 1, it is preferable to provide a triangular pyramid at the bottom of the lower part of container 2 (on the side of sealing 21) and start crystal growth from one point.
The slower the cooling rate of thallium bromide 1, the higher the purity of the crystal. An example of the cooling rate of thallium bromide 1 is 1 mm / h.

Further, the container 2 may be separated from the heater 62 by moving the heater 62 to the upper part of the container 2 (on the side of the quartz glass tube 22) instead of moving the container 2 by the elevating mechanism 63.
Furthermore, the heater 62 composed of a plurality of heaters may produce a temperature gradient by heating the thallium bromide 1 while performing precise temperature adjustment. A single crystal of thallium bromide 1 may be grown by a temperature gradient.

In addition, since the impure thallium bromide 12 is locked to the raw material fall prevention part 23, without removing the impure thallium bromide 12 from the container 2, thallium bromide 1 (purified thallium bromide 11) is obtained in the crystal growth step. Crystal growth becomes possible.

In the present embodiment, since the crystal growth process is performed using the container 2 oriented in a substantially vertical direction, the grown thallium bromide crystal does not come out of the surface of the liquid layer, and the crystal defects are few. High crystals can be obtained. In the present embodiment, the crystal is cylindrical and the temperature distribution is easily controlled, so that a large crystal growth is easily obtained.

In this embodiment, a series of steps such as a purification step, a separation step, and a crystal growth step are performed in the same vessel (crucible) without removing the raw material (thallium bromide) from the vessel (crucible). . By performing the series of operations using the same container in a closed system, a series of operations such as refining and crystal growth can be facilitated even for raw materials that require careful handling.

The crystal growth step is preferably performed in a container 2 arranged in a substantially vertical direction. By doing in this way, the crystal growth direction of thallium bromide coincides with the direction in which the internal space of the container 2 spreads. That is, even if thallium bromide crystals grow in the crystal growth step, the grown thallium bromide crystals do not come out of the melt surface. Therefore, a high-quality thallium bromide single crystal having a reduced crystal defect density, high charge carrier mobility, and high quality can be obtained.

Second Embodiment
A second embodiment will be described with reference to FIGS. 6 and 7. FIG. 6 shows an outline of the purification step S <b> 1 in this embodiment using the container 2 including the crystal purification unit 24 and the crystal growth unit 25. FIG. 7 shows an outline after completion of the separation step S2 in the present embodiment. In 2nd Embodiment, the structure of the container to be used differs from 1st Embodiment.
In addition, the same code | symbol is attached | subjected to the element same as above-described 1st Embodiment, and the overlapping description is abbreviate | omitted.

[container]
The container 2 used in the second embodiment includes a crystal purification unit 24 and a crystal growth unit 25.
For example, as shown in FIG. 6, the crystal refining unit 24 has a structure in which

quartz glass tubes

22 and 26 having a diameter smaller than that of the quartz glass tube are connected to both ends of a cylindrical quartz glass tube having both ends opened. For example, as shown in FIG. 6, the crystal growth unit 25 seals one end of a cylindrical quartz glass tube having both ends open (21), and connects the other end to a quartz glass tube 26 having a diameter smaller than that of the quartz glass tube. Has the structure. The crystal purification unit 24 and the crystal growth unit 25 are connected by a quartz glass tube 26. The crystal purification unit 24 and the crystal growth unit 25 do not have to have the same diameter, and it is preferable to reduce the diameter of the crystal purification unit 24 in order to improve the purification accuracy of thallium bromide 1 (raw material).

[Purification process]
The procedure of the purification step S1 is almost the same as in the first embodiment.
In this embodiment, thallium bromide 1 (raw material) is charged into the crystal purification unit 24 (see FIG. 6).
The initial position of the heater 3 during the purification of thallium bromide 1 is the crystal growth unit 25 side of the crystal purification unit 24. When refining, the temperature of the crystal growth part 25 is also maintained at least higher than the solidification temperature of the thallium bromide 1 by the auxiliary heater 32. This prevents thallium bromide and impurities from adhering to the crystalline growth portion 25.

[Separation process]
The procedure of the separation step S2 is almost the same as that in the first embodiment.

First, the container holding device 5 is adjusted, and the orientation of the container 2 is changed so that the crystal growth part 25 of the container 2 is positioned downward (see FIG. 7).
Next, on the surface of the container 2, a boundary portion between the purified raw material where the impurities of the thallium bromide 1 are reduced and the impure raw material where the impurities are increased by segregating the impurities, for example, bromide The heater 3 is arranged at a position about one fifth from the top of the thallium 1.

Then, the heater 3 heated on the surface of the container 2 moves slowly from the boundary toward the crystal growth portion 25 of the container 2, so that the thallium bromide 1 is separated and dissolved at the boundary. At the same time, the heater 3 moves the thallium bromide 1 having a high purity below the boundary to the crystal growth part 25 of the container 2 while dissolving it. The heating movement of the heater 3 may be performed a plurality of times. First, the heater 3 may heat the thallium bromide 1 at the boundary, dissolve it, separate it, and move it to the crystal growth part 25 of the container 2.

As a result, as shown in FIG. 7, solidified impure thallium bromide 12 having segregated impurities is present at the top of the container 2, and purified thallium bromide 11 is present in the crystal growth portion 25 of the container 2. It becomes.

[Crystal growth process]
(Sealing work)
The crystal growth step S3 of this embodiment is different from the first embodiment in that the purified thallium bromide 11 separated in the separation step S2 is melted and moved to the crystal growth portion 25, and then the crystal growth portion 25 and the crystal purification portion. The quartz glass tube 26 that connects to 24 is sealed off. By sealing the quartz glass tube 26 connecting the crystal growth unit 25 and the crystal purification unit 24, the volume of the container 2 is reduced, and the crystallized thallium bromide is difficult to evaporate and sublimate. Therefore, the storage stability of thallium bromide is further improved.

<Third Embodiment>
A third embodiment will be described with reference to FIGS. 8 and 9. FIG. 8 shows an outline of the purification step S1 in this embodiment using the container 2 including the crystal purification unit 27 and the trap unit 28. FIG. 9 shows an outline after completion of the separation step S2 in the present embodiment. In 3rd Embodiment, the structure of the container to be used differs from 1st Embodiment.
In addition, the same code | symbol is attached | subjected to the element same as above-described 1st Embodiment, and the overlapping description is abbreviate | omitted.

[container]
The container 2 used in the third embodiment includes a crystal purification unit 27 and a trap unit 28.
For example, as shown in FIG. 8, the trap portion 28 has a structure in which

quartz glass tubes

22 and 29 having a diameter smaller than that of the quartz glass tube are connected to both ends of a cylindrical quartz glass tube having both ends opened. About one quarter of the crystal purification unit 27 on the trap unit 28 side is reduced in diameter toward the quartz glass tube 22 and has a gentle taper shape. The crystal purification unit 27 and the trap unit 28 are connected by a quartz glass tube 22. The crystal refinement part 27 and the trap part 28 do not have to have the same diameter, and it is preferable to increase the diameter of the trap part 28 in order to increase the surface area in order to improve the collection performance of the trap part 28.

[Purification process]
The procedure of the purification step S1 is almost the same as in the first embodiment.
In the present embodiment, as shown in FIG. 8, thallium bromide 1 (raw material) is introduced into the crystal purification unit 27 through the trap unit 28.

The initial position of the heater 3 during the purification is the sealing 21 side of the crystal purification unit 27 (the right side in FIG. 8). When performing the purification, the temperature of the trap unit 28 is kept below the temperature of the crystal purification unit 27. The vapor containing impurities generated in the crystal purification unit 27 is cooled and solidified by the trap unit 28. Since the amount of impure thallium bromide separated in the separation step S2 is reduced, the work time of the separation step S2 can be shortened. Further, thallium bromide and impurities are difficult to get out of the container 2. Therefore, an external internal pressure adjusting substance supply device or the like is hardly contaminated by thallium bromide or the like.

[Separation process]
The separation step S2 is a step of separating the purified raw material, which is a portion in which impurities in the compound semiconductor crystal raw material are reduced by the purification step S1, and the impure raw material, which is a portion in which impurities are segregated to increase impurities. .
This embodiment is different from the first embodiment in that the portion of the thallium bromide 1 segregated impurity is moved to the trap portion 28.

Next, the direction of the container 2 is changed by adjusting the container holding device 5 so that the trap portion 28 of the container 2 is positioned downward (see FIG. 9). In this state, the purity of the thallium bromide 1 in the container 2 increases from the bottom to the top.
The heater 3 is arranged on the surface of the container 2 at the boundary between the refined portion of the thallium bromide 1 and the portion where impurities are segregated, for example, about one-fourth from the bottom of the thallium bromide 1. Is done.

Furthermore, the heater 3 heated on the surface of the container 2 moves slowly from the boundary toward the trap portion 28, so that the thallium bromide 1 is dissolved and separated at the boundary. At the same time, the heater 3 moves the impure thallium bromide 12, which has a low purity below the boundary and segregates impurities, to the trap portion 28 while dissolving it. The movement of the impure thallium bromide 12 also serves to clean the container 2 in order to dissolve impurities adhering to the container 2 during the movement. The trap portion 28 side of the crystal purification unit 27 is reduced in diameter toward the quartz glass tube 22 and has a gentle taper shape, so that the impure thallium bromide 12 is easy to move and hardly remains in the crystal purification unit 27.

(Sealing work)
The quartz glass tube 22 that connects the crystal purification unit 27 and the trap unit 28 of the container 2 is sealed to prevent impurities remaining in the trap unit 28 from being mixed into the crystal purification unit 27 during crystal growth. But you can. Further, the thallium bromide 1 for crystal growth is difficult to evaporate and sublimate in the crystal purification unit 27.

[Crystal growth process]
The procedure of the crystal growth step S3 is almost the same as in the first embodiment.
By adjusting the container holding device 5, the direction of the container 2 is changed so that the crystal purification unit 27 of the container 2 faces down. The heater 3 melts only the purified thallium bromide 1 left in the crystal purification unit 27 and moves it to the sealing 21 side of the crystal purification unit 27 (container 2). An auxiliary heater 32 may be used to melt the thallium bromide 1.

(Modification)
Although not used in the first to third embodiments, a furnace core tube may be disposed around the container 2 (crucible) in order to perform operation more safely. Further, a raw material refining boat may be separately prepared in the (crystal refining unit 24) of the container 2 and used to relieve the stress applied to the container 2.

The heating device used in the first to third embodiments is not limited to a heating wire that generates heat when energized, and may be, for example, a high-frequency heating device.
The container holding device 5 may be composed of a plurality of parts.

The container used in the present invention may be the container 2 including the crystal purification unit 27, the crystal growth unit 25, and the trap unit 28 shown in FIG.

The crystal refining unit 27 has a structure in which, for example,

quartz glass tubes

22 and 26 having a diameter smaller than that of the quartz glass tube are connected to both ends of a cylindrical quartz glass tube having both ends opened. The crystal growth unit 25 has a structure in which, for example, one end of a cylindrical quartz glass tube whose both ends are released is sealed, and a quartz glass tube 26 having a diameter smaller than that of the quartz glass tube is connected to the other end. The trap portion 28 has, for example, a structure in which

quartz glass tubes

22 and 29 having a diameter smaller than that of the quartz glass tube are connected to both ends of a cylindrical quartz glass tube having both ends opened.

The crystal growth unit 25, the crystal purification unit 27, and the trap unit 28 are connected by

quartz glass tubes

22 and 26 in this order. The crystal growth unit 25 and the crystal purification unit 27 do not have to have the same diameter, and the crystal purification unit 27 preferably has a small diameter in order to improve the purification accuracy of thallium bromide 1 (raw material).

By using the container shown in FIG. 10, even when a raw material having a large concentration gradient is purified, the raw material portion having a large amount of impurities is moved to the trap portion 28, and the purity of the raw material portion having a small amount of impurities is particularly high. The portion can be moved to the crystal growth portion 25. That is, considering the concentration gradient of the purified raw material, it becomes possible to sort the purified raw material according to the degree of purification of the raw material.

In the first to third embodiments, thallium bromide is exemplified as the crystal to be grown. However, the crystal to be grown is not limited to this. For example, in addition to various compound semiconductors such as cadmium telluride (CdTe), cadmium zinc telluride (CdZnTe), gallium arsenide (GaAs), mercury iodide (HgI ₂ ), and the like. It can also be applied to (single) crystal growth other than compound semiconductors.

As described above, the crystal growth method according to the present invention has been described in detail with reference to the embodiment. However, the scope of the present invention is not limited to the above-described content, and the scope of the right is based on the description of the claims. Must be interpreted. In addition, it cannot be overemphasized that the content of this invention can be changed or changed based on the above description.

1 Raw material (thallium bromide)
11 Purified raw material (purified thallium bromide)
12 Impure raw material (impure thallium bromide)
2 Container 21 Seal 22 Quartz glass tube 23 Raw material fall prevention unit 24 Crystal purification unit 25 Crystal growth unit 26 Quartz glass tube 27 Crystal purification unit 28 Trap unit 29 Quartz glass tube 3 Heater 32 Auxiliary heater 4 Heater moving device 5 Container holding device 6 Crystal Growth Device 61 Heat Insulating Material 62 Heater 63 Elevating Mechanism

Claims

The crystalline raw material is housed in a tubular container with one end closed, and the tubular container is made substantially horizontal, and then the portion of the crystalline raw material housed in the tubular container melted in a band from one end to the other is made substantially horizontal. A purification step of sequentially moving in the direction to segregate impurities contained in the crystalline raw material to the other end of the crystalline raw material;
A separation step of partially melting the crystalline raw material in which impurities are segregated to separate a purified raw material with less impurities and an impure raw material with more impurities;
In the container in a substantially vertical direction, while the impure raw material is separated in a solidified state, the purified raw material is brought into a molten state and then cooled to grow crystals, and
Are performed in the same container in this order.
The separation step is a step of separating the crystalline raw material into the purified raw material and the impure raw material in the container,
The crystal growth method according to claim 1, wherein the purification step, the separation step, and the crystal growth step are continuously performed.
The container includes a raw material refinement unit having a thin tube shape, and a crystal growth unit having an inner diameter equal to or larger than the material refinement unit,
The raw material refinement section and the crystal growth section are connected by a reduced diameter section,
Performing the purification step in the raw material purification section;
The crystal growth method according to claim 1, wherein the crystal growth step is performed in the crystal growth part after the purified raw material is moved to the crystal growth part.
The container includes a raw material purification unit having a thin tube shape, and a trap unit that cools to a temperature equal to or lower than the temperature of the raw material purification unit.
The raw material purifying section and the trap section are connected by a reduced diameter section,
Performing the purification step in the raw material purification section;
The crystal growth method according to claim 1, wherein the crystal growth step is performed in the raw material purification unit after the impure material is moved to the trap unit.
The crystalline raw material is housed in a tubular container with one end closed, and the tubular container is made substantially horizontal, and then the portion of the crystalline raw material housed in the tubular container melted in a band from one end to the other is made substantially horizontal. A purification step of sequentially moving in the direction to segregate impurities contained in the crystalline raw material to the other end of the crystalline raw material;
A separation step of partially melting the crystalline raw material in which impurities are segregated to separate a purified raw material with less impurities and an impure raw material with more impurities;
In the container in a substantially vertical direction, the refined raw material is a crystal growth method in which the refined raw material is melted and then cooled to grow crystals to continuously grow in the same container in this order,
The container includes a raw material purification unit having a thin tube shape, and a trap unit that cools to a temperature equal to or lower than the temperature of the raw material purification unit.
The raw material purifying section and the trap section are connected by a reduced diameter section,
Performing the purification step in the raw material purification section;
The separation step is a step of separating the crystalline raw material into the purified raw material and the impure raw material in the raw material purification unit,
After moving the impure material to the trap part, the trap part is separated from the container,
The crystal growth method, wherein the crystal growth step is performed in the raw material purification unit.
The movement of the purified raw material in the container is performed by dissolving the purified raw material,
The crystal growth method according to any one of claims 1 to 5, wherein the impurity raw material in the container is moved by dissolving the impurity raw material.
The crystal growth according to claim 6, wherein the container includes a raw material fall prevention unit that prevents any one or more of the crystalline raw material, the refined raw material, and the impure raw material contained therein. Method.