JP2000226300A - Method and apparatus for synthesizing and growing crystal - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing a highly pure polycrystal compound and single crystal compound in accurate stoichiometric ratio. SOLUTION: This method for producing a highly pure group II-VI or III-V polycrystalline compound in accurate stoichiometric ratio comprises the following steps: (a) heating an enclosing agent to a first temperature sufficient to melt the enclosing agent; (b) enclosing at least two reactants 26 and 28 in the stoichiometric amounts with the molten enclosing agent (the reactants 26 and 28 does not reach the temperature sufficient to cause the evaporation of one or more of the reactants during the enclosure); and (c) forming the polycrystalline group II-VI or III-V compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates generally to a method and apparatus for synthesizing polycrystalline compounds and growing single crystals from such compounds. In particular, the present invention relates to a high purity and precise stoichiometric Group II-VI comprising one or more reactants or dopants that are highly volatile at temperatures below the melting point of the selected encapsulant. And III-V
The present invention relates to a method and apparatus for synthesizing group III polycrystalline compounds and for growing single crystals from such compounds using known crystal growth techniques.

[0002]

Many Group II-VI compounds such as CdTe have been used in a wide range of semiconductor applications, including optical applications in the manufacture of detectors for high energy particles such as gamma and X-ray particles, and It is suitable for use as a substrate in structures having HgCdTe used in infrared detectors and solar cells. For example, European patent application EP 0 886 167 in the name of the applicant describes, in particular, an optical switchgear using an indium-doped CdTe crystal. Such applications require that the single crystalline material be of high purity and high crystallinity.

While the growth of large quantities of high quality silicon-based single crystals has been possible for many years, this is not the case for II-VI and III-V compounds. Various compounds of elements belonging to groups II and VI, in particular CdT
The growth of single crystals with the desired stoichiometric ratio from e can be due to the volatility of one or more of these elements, and sometimes due to the large difference in vapor pressure between the components of the compound at high temperatures and low thermal conductivity. Especially complicated. In addition, during alloy preparation, reactants segregate due to differences in the composition of the solid and liquid phases in equilibrium at a given temperature, resulting in localized concentrations of reactants, impurities, dopants, or fine phases. Produces a uniform distribution. Further, at temperatures where growth normally occurs, reaction of the reactants or compounds with the container material can result in contamination of the crystals. Crystal growth may also be adversely affected by high impurity content, dislocation density, or excess of one component that is too high and / or non-uniform in distribution, resulting in non-stoichiometric compounds and / or electronic properties. This results in damaged crystals.

Related art teaches various methods for synthesizing Group II-VI semiconductor compounds, among which are solid state reaction methods and gas phase synthesis methods. N. N. Kole
Snikov et al., "Growth and Chara
cterization of P-Type Cd
_1-x Zn _x Te (x: 0.2, 0.3, 0.4) ", J. Am .
Crystal Growth , vol. 2
56-262 (1997) describe the synthesis of CdTe by solid-state reaction of Cd in a sealed silica ampoule with excess Te. The same article also describes the vapor phase synthesis of ZnTe by the reaction of Zn vapor evaporated from a separate source and excess Te vapor at 1050 ° C. in a sealed silica ampoule.

F. P. Doty and J.M. F. Butl
er, "Properties of CdZnTe
crystals grown by high pr
essure Bridgeman method ",
J. Vac. Sci. Technol. B10
(4), pp. 1418-1422 (July / August, 19
92) Crystal growth in which the filler material is heated in a high purity graphite crucible with a firmly fixed cap to reduce the evaporation loss of the charge material in a programmed procedure for melt reaction and homogenization. The method is described.

Table I of the article shows the filler material lost during the growth of CdZnTe crystals. Various semiconductor single crystal growth techniques for Group II-VI compounds are known in the art, especially for the compound CdTe. One known growth technique is the Bridgman method of vertical (VB) or horizontal (HB) growth. Dissertation “Crystal G
row of Large-Area Single
e-Crystal CdTe and CdZnTe
by the Computer-Control
ed Vertical Modified-Brid
gmanProcess ", J. Crystal Gr
owth , vol. 86 (1988), pp. 146-64 . 111-11
7, (S. Sen et al.) Describe a special VB-type growth method used to grow CdTe crystals.
The equipment used includes a hot zone separate from the cold zone, and the two zones are arranged vertically to allow control of the thermal gradient between these zones. The polycrystal used for growth is obtained by a gas phase reaction of the components.

[0007] Yellin, N .; And Szapir
o, S. , “Vapor Transport of
Nonstoichiometric CdTe in
Closed Ampoules ", J. Cryst
al Growth , Vol. 555-60
(1984) describe a method of physical vapor transfer ("PVT") growth. First, polycrystalline CdTe was synthesized by a low-temperature reaction of Cd and an excessive amount of Te in a quartz ampoule having a fixed volume and sealed in a high vacuum. Next, the polycrystalline C
The dTe was transferred to a growth ampule and a single crystal was grown by vertical seedless growth (VUVG) at a temperature of 930-933C.

[0008] Another known growth technique is the liquid encapsulant Czochralski method (LEC). Crystal Growth Processes for GaAs Growth
(John Wiley & Sons, 198
6), pp. 151-54, J.I. C. Brice
Describe a method wherein the basis is to have no gas phase. The method comprises placing an amount of a growing substance and an encapsulant in a crucible heated by a high frequency electric field. First, the encapsulant melts to separate the molten material from the crucible, coating the crystals and the surface of the molten material. The seed crystal is brought to the surface of the liquid and grown under pressure by known methods, but the seed crystal is coated with an encapsulant that prevents decomposition. B ₂ O ₃ is mentioned as a suitable encapsulant.

US Pat. No. 4,740,264 describes a growth method using the float zone technique (floating zone method), in which a rod of crystalline material such as GaAs is embedded in a support structure. An encapsulant, such as B ₂ O ₃ , which has a lower melting point than the crystalline material, is placed between the crystalline material and the surrounding support structure. Before melting the bar,
The vessel is heated using a resistive heating coil to melt the encapsulant surrounding the bar, so that all of the support structure, encapsulant and bar are heated. The support structure is moved longitudinally through the heating zone and continuously melts the bar cross section as in a conventional float zone method.

US Pat. No. 5,057,287 teaches II
A growth method is described for -V and II-VI crystals, in which seed crystals (e.g., GaAs), pre-combined crystalline material (e.g., polycrystalline GaAs) and encapsulant are placed in an oven. And subsequently passed through three furnace zones. The area of the first furnace is maintained at a temperature above the melting point of the encapsulant and below the melting point of the crystalline material, and the area of the second furnace is shorter in length than the length of the vessel and at least below the melting temperature of the crystalline material. Maintained at an equal temperature, the area of the third furnace is maintained at a temperature above the melting point of the encapsulant and below the melting point of the crystalline material.

Another method for growing Group III-V and Group II-VI crystals is described in US Pat. No. 5,131,975. According to that method, small pieces of boron oxide encapsulant are dispersed in a finely ground compound semiconductor filler in a crucible also containing seed crystals. The temperature of the crucible is initially raised to a value above the melting point of boron oxide, which causes the boron oxide to have a sufficiently uniform liquid between the walls, the bottom of the crucible, and the semiconductor, which is still in a solid state. Form a layer. The temperature is then raised to near the melting point of the compound semiconductor material and crystal growth proceeds by a liquid encapsulant vertical cooling gradient growth process.

[0012] Tomoki Inada et al., "Grow
the of Semi-Insulating GaAs
s Crystals with Low Carbo
nConcentration Using Pyro
lytic BoronNitride Coated
Graphite ", Appl . Phys . Let.
t. 50 (3), pp. 143-145 (1987, January 1)
(May 19) describes a method for minimizing the incorporation of carbon into GaAs crystals grown by an in-situ synthetic liquid-filled Czochralski method under an Ar gas atmosphere. The method involves the use of a pyrolytic boron nitride coated graphite component in a large puller.

US Pat. No. 4,652,332 discloses Cu
A method for synthesizing and growing InSe ₂ (I-III-VI) single crystal is described. -The Applicant has noticed an obvious error in the specification of said US patent, but believes that the temperature in Celsius in the specification should in fact be expressed in Fahrenheit. For example, in column 5, lines 21-22, "B
₂ O ₃ begins to soften at about 700 ° C. ”. The Handbook of Chemist
ry and Physics , p. B-79 (66th
Plate, 1985-86) is 450 ° C. as the melting point of B ₂ O _3.
Is given. 450 ° C. is 723 ^° K. The described method uses stoichiometric amounts of Cu, In and Se to form B ₂
Comprising placing in a crucible with O ₃ . Cu,
In, Se and B ₂ O ₃ are heated under pressure by an RF induction heating coil. The increase in temperature causes liquefaction of B ₂ O ₃ , coating the crucible with Cu, In and Se, and also causing Se to begin significant evaporation. But B ₂
Because O ₃ is relatively soft and easy to melt, most of the selenium is trapped in the crucible. As the temperature increases, the Cu, In and Se inside the crucible form molten and encapsulated CuInSe ₂ , and the temperature further increases to homogenize the compound. Next, the molten CuInS
Insert the seed crystal through a encapsulant in contact with e _2, then by pulling it again an appropriate rate, a crystal is grown. The patent states that despite the presence of the encapsulant in combination with an excess pressure of 55-70 atm, there is still some Se loss from the crucible during the process, thereby preventing stoichiometric growth of the crystals. It is disclosed that there is a possibility. To solve this problem, the patent discloses that to compensate for these losses and obtain the correct final conditions for stoichiometric growth, the crucible has an extra 1.8%
It teaches adding 2.0% Se.

For the above reasons, it is clear that considerable effort has been made to improve the quality of grown crystals with respect to known techniques for the synthesis and growth of single crystals, including the use of liquid encapsulants. is there. These efforts include, inter alia, improving the growth equipment, selecting the proper materials for the equipment structure, special temperature gradients for the growing crystals,
Or generating various temperature changes over time and adding excess reactants to compensate for the vaporization of the reactants.

However, the applicant has not found any teaching in the prior art which uses the encapsulant method for the synthesis of Group II-VI polycrystalline compounds for growing Group II-VI single crystals.

This may be due to the fact that many of the Group II and Group VI elements begin to evaporate significantly at temperatures below the melting temperature of the encapsulant, such as B ₂ O ₃ . That is, in prior art methods, where melting the encapsulant would necessarily heat the reactants, one or more volatile reactants may be present before melting of the encapsulant and coating of the reactants is complete. Begin to evaporate unhindered by the encapsulant, resulting in the formation of non-stoichiometric polycrystalline compounds. Thus, since the starting material for single crystal growth is non-stoichiometric, the above growth method will produce Group II-VI single crystals with incorrect stoichiometry and / or impaired electronic properties. Would.

The inventors have determined, inter alia, that the solid state reaction method does not guarantee complete reaction of the elements. Polycrystals obtained in this way can be very non-stoichiometric.
The incorrect stoichiometry is described in F.S. P. It can also occur with closed ampoule synthesis methods, such as those described in the article cited by Doty et al.

The inventors have recognized that gas phase synthesis is generally used for the small scale production of compounds and requires a long synthesis time. Furthermore, the equipment used to carry out this method is complicated by the need to avoid loss of reactant vapors. For example, Cd and Te vapors are dangerous because they can cause cancer.

[0019]

According to the invention embodied and broadly described herein, in one aspect the invention is a method comprising:
Includes a method for producing Group II-VI or Group III-V polycrystalline compounds of high purity and precise stoichiometry. The method includes heating the encapsulant to a first temperature sufficient to melt the encapsulant; surrounding a stoichiometric amount of at least two reactants with the encapsulant in a molten state (during the encapsulation, the The reactants do not reach a temperature sufficient to cause vaporization of one or more of the reactants); and forming a polycrystalline Group II-VI or Group III-V compound from the reactants Comprising.

Typically, the step of surrounding a stoichiometric amount of at least two reactants with the encapsulant in a molten state further comprises: melting the reactants surrounded by the encapsulant by melting the reactants; Heating the reactants to a second temperature sufficient to cause the reactants to react with each other to form a reaction product; and bringing the reaction product to a third temperature sufficient to melt the reaction product; Heating for a time sufficient for the product to synthesize and homogenize.

The present invention also includes a method of producing a highly pure and accurate stoichiometric polycrystalline compound comprising the steps of: stoichiometrically adding at least two reactants to a first region. Placing a sufficient amount of encapsulant in the second area when the encapsulant is in a molten state (the second area is the first area of the encapsulant in a molten state) to completely surround the reactants. Wherein the first and second zones can be heated separately from each other); creating a gas atmosphere around the first and second zones, wherein the atmosphere is substantially at a selected maximum operating temperature. Pressurizing to a pressure above the vapor pressure of most of the volatiles of the reactants; heating the second region to a first temperature sufficient to melt the encapsulant without heating the first region. (The first zone is at a temperature sufficient to avoid vaporization of the reactants. To move the encapsulant in a molten state from the second region to the first region to surround the reactants); The body is melted and heated to a second temperature sufficient to cause the reactants to react with each other to form a reaction product; and the reaction product is heated to a third temperature sufficient to melt the reaction product And heating for a time sufficient to synthesize and homogenize the reaction product.

The present invention also includes a process for producing a highly pure and accurate stoichiometric polycrystalline compound comprising the steps of: a) stoichiometric at least two reactants in a vessel B) placing an amount of encapsulant sufficient to completely surround the reactants in the second area of the container when the encapsulant is in a molten state (where the second area is Suitable for transferring the encapsulant in the molten state to the first region, the second region being directly adjacent to the first region, the first and second regions being able to be heated separately from each other) ;
c) placing the vessel in a sealed, vertically disposed chamber; d) creating a gas atmosphere in the vessel, wherein the atmosphere is substantially volatilized at a selected maximum operating temperature with substantially all of the reactants E) heating said second region to a first temperature sufficient to melt said encapsulant, while said first region is sufficiently pressurized to avoid vaporization of said reactants. At a suitable temperature, thereby causing the encapsulant to move from the second region to the first region in a molten state to surround the reactants; f) removing the reactants surrounded by the encapsulant Heating the reactants to a second temperature sufficient to cause the reactants to melt and react with each other to form a reaction product; and g) sufficient to cause the reaction product to melt At a suitable third temperature and the reaction products are synthesized and homogenized. A sufficient period of time, is heated to.

The method further comprises, after step (g), the step of: enclosing the reaction product surrounded by the encapsulant at a temperature below the melting point of the reaction product, but of the encapsulant. Cool to a temperature above the melting point; and separate the reaction product from the encapsulant.

Preferably, the reactants are at least one
One Group II element and at least one Group VI element;
Alternatively, it comprises at least one Group III element and at least one Group V element. More preferably, the reactants are Cd and Te.

Preferably, the vessel in which the reactants are located is
Combine with at least one other container. More preferred
The crucible is movably inserted into the container. advantageous
Is used in the method for producing a polycrystalline compound
The mounting medium is B _TwoO_ThreeIt is.

Preferably, the inert gas used in the method for producing a polycrystalline compound is an argon gas. Preferably, the pressure in the chamber is about 10 a
tm to about 100 atm.

[0027] More preferably, the pressure in the chamber is about 20 atm. Preferably, the first temperature in step (e) is at least the melting point of the encapsulant.

Preferably, the second temperature in step (f) is at least the melting point of the reactant with the highest melting point. Preferably, the third temperature in step (g) is at least the melting point of the reaction product.

Typically, the reaction product is a polycrystalline compound. Preferably, the reaction product is CdTe. In another aspect, the invention includes a polycrystalline compound produced by the above method of producing a polycrystalline compound. Preferably, said polycrystalline compound has a purity of at least about 5N.

Preferably, said second region of said method for producing a polycrystalline compound comprises a heating element. Advantageously,
The encapsulant is added to the chamber in step (e) to an extent sufficient to induce current in the heating element by current from a power source without inducing current in the reactants in the first region. The container is melted by moving the container in the chamber with respect to the power source.

Preferably, in the method for producing a polycrystalline compound, the reactant is used in the step (f),
By moving the vessel in the chamber relative to the power source in the chamber sufficient to induce a current in the reactant by the current from the power source;
Heated.

Preferably, during step (g), the reaction product is rotated. Preferably, the heating element is in contact with the encapsulant. Preferably, said heating element is selected from the group consisting of liquid gallium and liquid indium. More preferably, the heating element is in a receptacle in the container.

Preferably, said heating element consists essentially of a graphite disk coated with pyrolytic boron nitride. In another aspect, the present invention includes a method for producing a single crystal of high purity and precise stoichiometry from a polycrystalline compound produced by the method, the method further comprising: housing Placing the seed single crystal within the first region of the container; performing steps (a)-(g); and gradually lowering the container with respect to the chamber, thereby reducing the volume of the first region. The temperature is gradually lowered to grow the single crystal.

In another embodiment, the present invention comprises a method of making an encapsulated reactant composition comprising the steps of: bringing an encapsulant to a first temperature sufficient to melt said encapsulant. Heating; and disposing the stoichiometric amount of at least two reactants in the molten state before the reactants reach a temperature sufficient to cause vaporization of one or more of the reactants. With an agent (the reactant comprises at least one Group II element and at least one Group VI element).

The present invention also includes an encapsulated reactant composition comprising at least two reactants surrounded by an encapsulant, wherein the reactants comprise at least one II.
A group element and at least one group VI element, or at least one group III element and at least one group V element.

In another embodiment, the present invention comprises a polycrystalline compound, wherein the compound comprises at least one Group II element and at least one Group VI element, or at least one Group III element and at least one It comprises a Group V element and has a purity of at least about 99.998%, and any of the elements that make up the compound may have a purity of about 0.9%.
More than 01 mol% does not deviate from the stoichiometric composition.

In another embodiment, the present invention comprises a method of producing a single crystal of high purity and precise stoichiometry comprising the steps of: a) melting the encapsulant, wherein said encapsulant melts B) removing at least two reactants in a stoichiometric amount to a temperature sufficient to cause vaporization of one or more of the reactants to occur. Then, it is surrounded by the encapsulant in a molten state (the reactants
Comprising at least one Group II element and at least one Group VI element); c) reacting the reactants surrounded by the encapsulant such that the reactants melt and the reactants react with each other. Heating to a second temperature sufficient to form a reaction product; d) bringing the reaction product to a third temperature sufficient to melt the reaction product and synthesizing and homogenizing the reaction product And e) forming a single crystal from the reaction product. Preferably, the encapsulant of step (a) forms a liquid. Preferably, the single crystal of step (e) is formed by growth.

In another embodiment, the present invention comprises a method of producing a single crystal of high purity and precise stoichiometry comprising the following steps: by the above method of producing an encapsulant reaction product Producing an encapsulated reaction product; heating the reaction product to a molten state; inserting a seed single crystal into the reaction product; and gradually pulling up the seed single crystal from the molten reaction product. .

In another embodiment, the present invention comprises a single crystal of high purity and precise stoichiometry, wherein the single crystal comprises at least one Group II element and at least one VI
A group III element or at least one group III element and at least one group V element and having a purity of at least about 99.9998%.

In another aspect, the present invention comprises an apparatus for producing a polycrystalline compound having high purity and precise stoichiometry comprising: a furnace having at least one chamber; A container in the chamber having a first region for containing the reactants, and at least a second region for containing the encapsulant and a heating element; a heater for the encapsulant; rotating the container in the chamber Means for allowing and vertically supporting and moving;
And independent heaters for the first and second regions of the vessel. Preferably, the furnace includes at least one window.

In yet another aspect, the invention includes an apparatus for producing a polycrystalline compound having high purity and precise stoichiometry comprising: at least one vertically disposed Furnace having a closed chamber; a first region for containing the reactants, and a second region immediately above the first region for containing an encapsulant and a heating element for heating the encapsulant. A container in the chamber having a region; a member connected to a motor for rotatably and vertically supporting and moving the container in the chamber; and a member surrounding the second region of the container. An electric current for inducing a current in the heating element without heating the first region of the container, and for inducing a current in the reactant when surrounding the first region of the container. Power induction heating coil. Preferably, said container is associated with at least one other container. Preferably, the crucible is rotatably inserted into said container.

It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. The following description sets forth and suggests additional advantages and objectives of the present invention, as well as examples of the present invention.

[0043]

DETAILED DESCRIPTION OF THE INVENTION The present invention provides novel polycrystalline compounds for use in a wide variety of semiconductor applications, and novel methods and apparatus for producing novel single crystals formed from such compounds. The invention further provides novel novel polycrystalline compounds and novel encapsulated reactant compositions for producing single crystals.

The present invention provides a method and apparatus for producing high purity and accurate stoichiometric crystalline compounds.
As used herein, "high purity" refers to at least about 99.999%, preferably at least about 99.9997%, and most preferably about 99.999%, for a polycrystalline compound.
Defined as 9999% purity. For single crystals, high purity is at least about 99.999%, preferably at least about 99.99998%, and most preferably about 99.9999%.
Defined as 9.999999% pure. Generally, the degree of impurity in a sample of a substrate is calculated by evaluating the ratio, expressed as a percentage, between the weight of the impurity having the largest weight contained in the sample and the total weight of the sample. Purity is defined as 1 minus the impurity concentration. Furthermore, it is common in the art to indicate the purity of a sample by indicating how many of the first digits correspond to "9" in the above defined purity. That is, for example, a purity corresponding to 99.99% indicates a purity of 4N. Therefore, at least 9
A purity of 9.998% corresponds to a purity of at least 5N. "Stoichiometry" discusses combining the weights of elements and compounds using a ratio that allows one to calculate the number of moles of one substance over the number of moles of another substance.

For the purposes of the present invention, the term “filling material” refers to a substance, including elements, compounds, and dopants, that is introduced into a suitable container that forms a synthetic or growth step product at the end of the process. means.

By the term "compound" is meant a substance consisting of two or more atoms or elements that are chemically bonded in a defined weight ratio. By the word "alloy"
A mixture (liquid or solid) of two or more elements which can have various weight ratios is meant.

By the term crystal is meant a homogeneous solid consisting of a mixture of elements, chemical compounds or isomorphous crystals in which the atoms or molecules are arranged in a regularly repeating pattern.

The term “monocrystalline” (“monocrystal” or “single crystal”) means
All parts mean crystals having the same crystallographic orientation.
The term "polycrystalline" means a substance consisting of aggregates of individual crystals.

Furthermore, in the context of the present invention, the terms "polycrystalline compound" and "monocrystalline compound" are used to refer to compounds or alloys which have a polycrystalline and monocrystalline structure, respectively, and which may contain dopants. Means

The method of the present invention comprises several steps. First, a stoichiometric amount of at least two reactants is placed in a first region of the vessel. The method is particularly suitable for preparing compounds from one or more reactants that are highly volatile below the melting point of the chosen encapsulant and / or volatile at temperatures near the melting point of the encapsulant. ing.

Applicants note that in accordance with the present invention, large quantities of these elements are prevented from undergoing sublimation and then disappearing before the encapsulant is completely melted and covers the filler material. I have.

Suitable elements include Ce, Zn, Hg, T
e, Se, Ga, As, In, Tl, Mg, Sb, G
e, Ag, Cu, P, Se, and S are included. Preferably, the at least one reactant is a Group II element, the at least one reactant is a Group VI element, or the at least one reactant is a Group III element;
At least one reactant is a Group V element.

The method comprises the steps of using CdTe, CdZnTe, and Cd, Hg, Se, Te, Z, which are relatively more volatile.
Particularly suitable for compounds having at least one of n, S, Sb, As, P, but the advantages are more limited to Bi, In, Ga, Te which are non-volatile.

Most preferably, the reactants are Cd and Te alone or in combination with one or more other elements or dopants. Suitable dopants include
In, Cl, I, B, Al, Ga, Fe, Cu, Ag,
Hg, Se, Zn, S, Se, Sb, As, and P are included.

As an example, dopants can be added to the filler material to obtain specific optoelectronic or structural properties. When a dopant is used in the method according to the invention, it is added together with the reactants at the beginning of the process.

The vessel in which the reactants are located may itself be combined with one or more other vessels. Preferably, the container is combined with a first combination container, hereinafter referred to as a crucible, for purposes of clarity, not limitation. Most preferably, the container is not limited,
For the sake of clarity, it itself holds a crucible containing the second combination container, hereafter called a receiver. One skilled in the art can easily determine the appropriate dimensions of the container, crucible and receiver.

Advantageously, the diameter to height ratio of the container is from about 1: 5 to about 5: 1. Preferably, the diameter to height ratio of the container is from about 1: 2 to about 2: 1. Most preferably, the diameter to height ratio of the container is about 1. Advantageously, the ratio of diameter to height of the crucible is from about 1: 5 to about 5:
It is one. Preferably, the ratio of diameter to height of the crucible is:
From about 1: 3 to about 3: 1. Most preferably, the crucible has a diameter to height ratio of about 0.7: 1. Advantageously, the diameter to height ratio of the receptacle is from about 10: 1 to about 1: 5. Preferably, the diameter to height ratio of the receptacle is from about 5: 1 to about 1: 2. Most preferably,
The receiver has a diameter to height ratio of about 1.2: 1.

Preferably, the container (or crucible, if present) has two regions that can be heated separately from each other and separated by separate shields, but preferably not separated. The container may also have more than one region. The container is supported by a member, preferably a shaft mounted on a motor, which provides for vertical, horizontal, or rotational movement of the container, or a combination thereof. Preferably, this member provides for vertical and rotational movement of the container. If the synthesis and / or growth occurs horizontally, the members will give a horizontal and rotational movement.

In the context of the present invention, the terms "means for rotatably and vertically supporting" and "means for moving" are used to refer to any device, machine, magnetic means, elastic means, electrical means suitable for the above purpose. Means, pneumatic means and other means.

[0060] The container and shaft can be composed of any suitable material or combination of materials known to those skilled in the art for such purpose. Suitable materials of construction include quartz, graphite, quartz coated with graphite, Al ₂ O ₃ and graphite coated with pyrolytic boron nitride (pBN).
PBN-coated graphite or Al ₂ for equipment parts in contact with encapsulants, reactants, polycrystalline compounds, or single crystals
The use of O ₃ is advantageous because the potential for silicon contamination inherent in the use of quartz is avoided. Therefore, the use of such materials would be expected to contribute to the production of high purity compounds.

Next, an amount of the encapsulant sufficient to completely surround the reactants when the encapsulant is in the molten state is placed in the container. Advantageously, the encapsulant is inert to the vessels, reactants and reaction products, adheres to the reactants, reaction products and growing crystals without damaging the crystals, has a relatively low melting point and a suitable density And can be easily removed from various components when synthesis and / or growth is complete. Suitable encapsulating agents include, for example, 1: include one of KCl-NaCl and B ₂ O _3. Preferably, the encapsulating agent is a B ₂ O _3. Preferably, the molten state is a liquid. The mounting medium,
It can be in the same area as the reactants or in a different area from the reactants.

[0062] Preferably, the encapsulant is in a second region different from the region containing the reactants and suitable for transferring the molten encapsulant to the first region containing the reactants. . Preferably, the encapsulant is directly adjacent to the reactants. Most preferably, the encapsulant is in contact with the reactants.

Next, a heating element is placed in the second region adjacent to the encapsulant to heat the encapsulant. The heating element is
Although not required, it is preferably in contact with the mounting medium. Most preferably, the heating element is in contact directly above the encapsulant. The heating element must be able to have a current induced on it in order to generate heat. Such a heating element is desirable because the encapsulant B ₂ O ₃ is electrically insulating and therefore cannot direct current to it to directly heat and melt it. Suitable heating elements include liquid gallium, liquid indium, other elements or compounds having a suitable low vapor pressure, or combinations thereof, which are preferably placed in a receptacle in the crucible, Also preferred are graphite, pBN-coated graphite, and SiC (silicon carbide) disks, but these need not be placed in the receiver. Most preferably,
The heating element is a graphite disc coated with pBN, according to which the dissolution of the graphite in the encapsulant and subsequent carbon contamination of the synthesized polycrystalline compound or impurities of the compound due to impurities contained in the graphite. Pollution is avoided.

The container is placed in a chamber containing a heating system. Preferably, the chamber is in a furnace and may have a window through which the contents of the chamber can be seen. The walls of the furnace may be surrounded by fluid cooling tubing that operates in conjunction with a conventional liquid circulation and cooling system. The fluid can be, for example, water.

The chambers can be arranged horizontally, but preferably the chambers are arranged vertically. The heating system used may be any suitable heating system known in the art, and may be stationary or may be movable vertically or horizontally. Preferably, the heating system is stationary. Suitable heating systems include graphite cylindrical heating elements, induction heating coils and resistive heating elements. A resistive heating element is an electrical element that generates heat under an applied current.

[0066] Preferably, the heating system is an induction heating coil with electric power. Preferably, the induction heating coil is combined with a fluid cooling system. The cooling fluid is, for example, water. Cooling fluid circulates through the coil to avoid overheating and breakage of the coil during operation. In addition, the fluid cooling system rapidly reduces the temperature of the coil when the heating device is switched off.

[0067] Most preferably, the heating coil comprises a copper coil winding that is powered by a high frequency generator. Appropriate dimensions of the heating system can be easily determined by those skilled in the art. Advantageously, if copper coil windings are used, they should have a diameter to height ratio of about 1: 5 to about 10: 1. Preferably, the ratio of diameter to height is about 1:
1 to about 2: 1. Most preferably, the ratio of diameter to height is about 1.7: 1.

Applicants have recognized that the heating coil must be such as to heat element 32 (FIG. 1) without heating the reactants during the first heating step. In that case, the upper limit of the height of the heating coil is not important.

The atmosphere of the inert gas is created in the chamber. Suitable inert gases can be readily determined by one skilled in the art and include argon and nitrogen. Generally, a gas of one of these components can be used. However, inert gases are preferred to avoid corrosion and safety issues.

Next, the atmosphere is pressurized. Preferably, the atmosphere is pressurized at a selected maximum operating pressure to a pressure substantially above the vapor pressure of most volatiles of the reactants. Preferably, the maximum operating temperature is higher than the melting temperature of the polycrystalline compound. More preferably, the atmosphere is pressurized to a pressure from about 10 atm to about 100 atm.

Most preferably, the atmosphere is about 20a
tm to about 40 atm. If the reactants are Cd and Te, the most preferred pressure is 20
atm.

Next, the heating element is heated to a temperature sufficient to melt the encapsulant. The heating element can be heated by any suitable means known to those skilled in the art that can heat the area containing the heating element without heating the area containing the reactants.
Preferably, the heating element is heated by a heating system. Most preferably, the container is positioned in the chamber such that the area containing the heating element is within the induction heating coil, while the first area containing the reactants is outside the induction heating coil. . Then, power is supplied to the induction heating coil sufficient to induce current in the heating element, and the heating element does not induce current in the reactants in the first region,
The encapsulant is heated and melted. Preferably, the encapsulant is heated to a temperature that is at least the melting point of the encapsulant. Since heating of the encapsulant does not induce current in the area where the reactants are located, vaporization of the reactants is minimized and helps maintain stoichiometry.

When the encapsulant melts, it moves to the area containing the reactants and surrounds the reactants. The area containing the reactants is not heated during the melting of the encapsulant and is therefore maintained at a temperature sufficient to avoid vaporization of the reactants. This does not mean that there is no vaporization of the reactants, but rather the vaporization that occurs is negligible,
Meaning does not significantly affect the stoichiometry of the polycrystalline compound formed. Since the lower region containing the reactants is heated only after the reactants have been coated with the molten encapsulant, vaporization is minimized and contributes to the synthesis of a product having the correct stoichiometry. In addition, since the reactants are not heated during the heating of the encapsulant, the length of time the polycrystalline compound is subjected to high temperatures is reduced, and contamination by the material comprising the crucible or container is reduced. Furthermore, the production of polycrystalline compounds having precise stoichiometry and low impurity content improves the quality of single crystals grown from such compounds.

According to one aspect of the invention, the reactants surrounded by the molten encapsulant constitute an inventive product. The reactants surrounded by the molten encapsulant can be cooled to a temperature below the melting point of the encapsulant, whereby the encapsulant solidifies around the reactants. The inventive product is then withdrawn, at some later time, from the vessel for the synthesis of the polycrystalline compound by a further process of the invention, or another process.

After the reactants have been surrounded by the molten encapsulant,
Heating is achieved by bringing the area containing the reactants surrounded by the molten encapsulant into the area of the heating system. To achieve this, the vessel may be moved such that the area containing the reactants is once occupied by the area containing the heating elements, or Instead of being located around the area in which the reactants are located, the heating system can be moved such that it is located around the area containing the reactants. Preferably, the vessel is moved to carry the reactants into the area of the heating system. Most preferably, the vessel is moved vertically to a position such that the heating coil surrounds the area containing the reactants.

The reactants are heated by melting the reactants and heating the system to a temperature sufficient to cause the reactants to react with each other to form a reaction product. Preferably, the reactants are heated to a temperature that is at least the melting point of the highest melting reactant. Preferably, the reactants are heated by direct current induction from a heating coil, thereby avoiding the use of heating substances such as graphite which can contaminate the compounds and reduce the purity of the resulting product. The reaction product is then heated to a temperature sufficient to melt the reaction product and for a time sufficient to synthesize and homogenize the reaction product. Preferably, the reaction product is heated to a temperature that is at least the melting point of the reaction product. Preferably, the reaction product is rotated by rotation of the vessel during melting, synthesis and homogenization.

Next, the reaction product is cooled to a temperature lower than the melting point of the reaction product and higher than the melting point of the encapsulant so that the reaction product solidifies and the encapsulant remains molten. The heating system is then switched off and the encapsulant cools and solidifies.

In addition, a cooling phase is rapidly created by the fluid cooling piping system associated with the furnace. The encapsulant is now removed by plunging the reaction product container into water (H ₂ O) or alcohol (ethyl or methyl). The encapsulant then softens and their separation occurs as the compound remains solid.

In water, the container may break due to the expansion of the encapsulant, while in alcohol the expansion is less rapid and the container is protected. Quartz container is pB
Not as expensive as N's.

The encapsulant softens the encapsulant and can also be decomposed by ultrasound without affecting the compound. The reaction product can be cooled by any suitable cooling means known to those skilled in the art.

An apparatus comprising a water-cooled heating system and a water-cooled furnace has low thermal inertia. Such a system allows for the synthesis of uniform alloys with relatively large amounts of reactants or dopants, while avoiding segregation, and thus the subsequent growth of crystals from such alloys. It offers the possibility of producing a great cooling gradient. The polycrystalline compound reaction product of the present invention can be used to grow single crystals of high purity and precise stoichiometry, and can be used in the growth methods and apparatus described below.

The following detailed description refers to the accompanying drawings. The same reference numeral indicates the same or similar element. The description includes exemplary embodiments, however, other embodiments are possible, and modifications may be made to the embodiments described without departing from the spirit and scope of the invention.
The scope of the present invention is defined only by the claims. In the description, for simplicity, reference is made to the synthesis and growth of CdTe. However, the concept of the invention described is
Other compounds and alloys of the II-VI group, such as CdS
binary, ternary or quaternary compounds and alloys, such as e, ZnTe, ZnSe and ZnCdTe, and semi-magnetic compounds and alloys, such as HgMnTe and CdMnTe, as well as materials doped with appropriate elements, eg, n or p-type dopants It can also be applied to synthesis and growth.

The same method and apparatus of the present invention may
It can be extended to the synthesis of Group IV compounds and alloys, antimonides, arsenides and ternary compounds. The method and apparatus of the present invention may be used to synthesize polycrystalline compounds other than Group II-VI or III-V compounds and alloys, for example,
CuInSe ₂ , AgGaSe ₂ , AgGaTe ₂ , Cd
The synthesis of GeAs ₂ , InS can be effectively used with only minor changes in the selection of feature parameters that are easily determined by those skilled in the art.

FIG. 1 is a diagram of a preferred embodiment of an apparatus consistent with the principles of the present invention suitable for the synthesis of, for example, CdTe compounds suitable for growing single crystals. The equipment is
Furnace 10 comprises a vertically disposed chamber 12 within which is located an induction heating coil 14 and further within the chamber is a vessel 16 which preferably includes a crucible 18. The receiver 20 can be inserted into the crucible 18. The container 16 is mounted on a shaft 22 that is rigidly connected to a motor 24 to allow rotation and vertical translation of the container 16 and, with it, the crucible 18 and receiver 20 relative to the heating coil 14. Preferably, container 16 and receptacle 20, crucible 18 and shaft 22 are made of quartz. Preferably, the furnace 10
Has a window, which makes the interior of the device visible.

[0085] More preferably, the walls of the furnace 10 are surrounded by water-cooled piping that cooperates with a conventional fluid circulation and cooling system (not shown). The fluid can be, for example, water. In accordance with the principles of the present invention, a preferred method of synthesizing compounds uses the novel apparatus described above and shown in FIG.
It will be clear from the description of the method carried out by the applicant for the synthesis.

The synthesis process was monitored and controlled by looking at the contents of the chamber through the windows described above.
In particular, changes in the state of the encapsulant and the filling material (melting, solidification) and chemical changes in the filling material were directly observed and / or inferred in a manner obvious to the person skilled in the art by a change in color of the filling material.

The melting point of the boron oxide encapsulant is T _m = 450 ° C.
Alternatively, T _m = 723 ^° K. Te is T _m = 430
It has a melting point of ° C. The vapor pressure P ⁰ _Te (bar) of _Te is
For any temperature T ( ^o K) it can be calculated from:
ogP ⁰ _Te = 4.7191-5960.2 / T. Tellurium vapor is mainly composed of (95%) diatomic molecules, ie, Te.
_{Consists of two} . The vapor pressure of Te ₂ at the melting point of B ₂ O ₃ is P
^{_{0 Te2 (723 o K) =}} 3.10 ^-4 bar.

Cd has a melting point of T _m = 320 ° C.
The vapor pressure P ⁰ _Cd (bar) of _Cd is equal to an arbitrary temperature T ( ^o K).
Can be calculated from the following equation: InP ⁰ _Cd = 26.15
-13859 / T-1.8415lnT.

The vapor pressure P ⁰ _Cd of Cd at the melting point of B ₂ O ₃
Is P ⁰ _Cd (723 ^° K) = 5.8 · 10 ⁻³ bar. Thus, it can be seen that Cd is more volatile than Te (because it has a higher vapor pressure), and the melting points of Cd and Te are both below the melting point of B ₂ O ₃ .

Applicants note that, according to conventional methods, complete melting of B ₂ O ₃ is achieved when the reactants have a temperature above 450 ° C., where the actual vapor pressure of the reactants is ,
It is recognized that it is higher than the above value.

Thus, prior to the present invention, one starts with at least one low fusogenic and / or highly volatile reactant,
The use of an encapsulant such as B ₂ O ₃ in the synthesis of CdTe or similar compounds has not been possible, however, because prior art methods heat the reactants to their melting points while heating the encapsulant. That is because it could not be avoided.

[0092]

EXAMPLE 1 In the first step of the preferred method, the preparation of the packing material, the reactants Cd26 and Te28 were charged with stoichiometric amounts, ie, 200.03 g of Cd and 227.08 g of Te to the crucible 18. Put in.

30 g of a B ₂ O ₃ encapsulant 30 having a height of about 3 cm
Was placed on top of reactants 26 and 28. The melting point of the boron oxide encapsulant was T _m = 450 ° C. The filling material (reactants 26 and 28) is applied to the first lower region D of the crucible 18
Accounted for. The receiver 20 containing the heating element 32 was placed on the pellet of the encapsulant 30. The heating element 32 has about 6
It consisted of 0 g of liquid gallium.

The encapsulant 30 and the receiver 20 are placed in the crucible 1
8 of the second upper region U. A heating element 32 was used to heat the encapsulant 30. Since B ₂ O ₃ is electrically insulating, it is not possible to induce a current directly therein by the heating coil 14.

The crucible 18 thus assembled is
Placed in container 16. The chamber 12 is 20 atm
And pressurized with high purity (99.999%) argon gas. This value is 1110 ° C., ie Cd and Te ₂ equilibrating with CdTe at the highest temperature expected in the crucible.
Greater than the vapor pressure of

The container 16 is then placed vertically, so that the heating coil 14 surrounds only the upper area U of the crucible 18, which corresponds to the area occupied by the heating element 32, as shown in FIG. did.

Next, electric power is supplied to the heating coil 14,
Heat was induced in the heating element 32 and transferred to the pellets of the encapsulant 30. The encapsulant 30 initially softened and melted at the top, ie, closest to the heating element 32, and then a first layer of liquid encapsulant covered the contents of the crucible 18. Finally, the encapsulant 30 was completely melted, as shown in FIG.

FIG. 4 is an approximate power-time diagram of the synthesis process according to the present invention. In FIG. 4, power is represented by an arbitrary unit. The first line fg is B ₂ O ₃
This corresponds to melting of the encapsulant 30. Liquefaction had a time of about 30 minutes. Melting of the encapsulant occurred without heating region D of crucible 18, maintaining the temperature in this region at a value that did not cause volatilization of the reactants. The line gh approximately corresponds to the waiting time required to cover the filling material.

Applicants have confirmed the complete coverage of the filling material by observing the contents of the chamber through the windows described above. The amount of gallium inside the receiver 20 was sufficient to allow the receiver 20 to float above the molten encapsulant 30. Alternatively, receiver 20 can be fixed to the wall of container 16.

Next, as shown in FIG. 2, the container 16 was moved vertically, and the reactants 26 and 28 and the molten encapsulant 3 were removed.
The low area D of the crucible 18 containing 0 was within the range of the heating coil. Next, the power supplied to the heating coil 14 was gradually increased to melt the reactants Cd26 and Te28, and then caused an exothermic reaction, which was accompanied by a flash of light. In FIG. 4, a line hi indicates the power-time relationship of the reaction stage. Reactants 26 and 28 contain molten B ₂ O ₃
Only after it has been completely coated with the encapsulant 30 is it heated, which prevents it from evaporating during the reaction phase. Importantly, heating of the reactants 26 and 28 occurs by exploiting their inherent conductivity, and thus directs current directly into the reactants to support the crucible 18 and from graphite or other materials. The use of a heating element made was avoided.

The line i-l corresponds to a pause between the reaction stage and the subsequent melting stage (lm). The time is not important and this step can be skipped. The power of the heating coil 14 is then further increased (lines mn) to melt and homogenize the liquid and ensure complete reaction of the reactants and the reacted CdTe (the melting point of _CdTe is T _CdTe = 1092
° C) was melted. During this state, the crucible 18 was rotated (by the shaft 22 and the container 16) at a speed of 5 to 10 rpm (rotation speed per minute) for about 30 minutes. The line mn is
Corresponding to the steps required to homogenize the molten compound).

Applicants have observed the melting of the light yellow reacting compound through a suitable window and transparent melt encapsulant. As shown in FIG. 4 (line n-p), the heating coil 1
The power of 4 was reduced for about 120 minutes, while at the same time the compound was cooled by moving the first container 16 downward as in FIG. In this state, the reacted CdTe 34 solidified, while the layer of encapsulant 30 was maintained in a liquid state.

Since B ₂ O ₃ has a weight density lower than that of CdTe, the layer of the encapsulant 30 is made of CdTe.
Floated over 34 reaction compounds. The synthesis process was monitored and controlled by viewing the contents of the chamber through the window.

The above device allowed rapid cooling, also because the pressurized atmosphere of the furnace had a high thermal conductivity which ensured relatively high heat loss from the walls of the device.
Next, the high-frequency power supplied to the heating system was turned off, and the mounting medium was cooled.

Water cooling in the heating system and furnace allowed for rapid cooling of the encapsulant. The crucible 18 was removed from the chamber 12 when the system returned to room temperature. Applicant:
No condensation of the reactants was observed on the walls of chamber 12. This indicates that no gas reactant escaped from the encapsulant 30 during the process. Further evidence of this was obtained by weighing the synthesized CdTe compound, which did not show any significant reduction in weight relative to the initial amount of reactants 26 and 28.

Applicants have recognized that in the case of the synthesis of doped fillers or alloys, the cooling rate can be increased moderately to avoid segregation of reactants or dopants. This is made possible by the device according to the invention, which has a low thermal inertia.

Other temperature gradients, different from those described above, are possible and can be easily modified by those skilled in the art, but to avoid segregation of reactants or dopants, the synthesis of ternary and quaternary compounds or alloys requires: Alternatively, it is particularly useful when a dopant is used. The pressure used in chamber 12 for the synthesis of compounds different from CdTe also
Those skilled in the art can easily determine.

The obtained polycrystalline compound was purified by using E
A comparison was made with a commercially available polycrystalline compound obtained from SPI.
Weight ppm (ppm) for each detected impurity
To evaluate the content in w), these polycrystalline compounds were analyzed (ppmw = weight of impurities [μg] / weight of compound [g]).

Table 1 shows the results of the analyzes performed. The first column shows the chemical symbols of the possible impurities, and the second and third columns show the ppmw values for the comparative sample of the polycrystalline compound and that produced by the method described in Example 1, respectively. Show. Blank columns in the table correspond to those where there is no measurable amount of impurities.

[0110]

[Table 1]

Table 1 shows that the comparative polycrystalline compounds (especially,
Elements Ti, V, Ag, In, Sn, Sb, Tl, Pb,
It is clear that many of the impurities found in Bi) are not present in the compounds produced by the method and apparatus of the present invention. Although large amounts of B and Se are present in the polycrystalline compounds of the present invention, as discussed below, these levels are not appreciable for single crystal growth and performance. In particular, Applicants speculate that Se arises from its impurities present in the Te reactant, and therefore its presence is independent of the synthesis process.

Further, since Se is isoelectric with Te, its electric characteristics are as follows.
It does not adversely affect the behavior of Te. Applicants have performed another CdTe polycrystalline synthesis using the Te samples obtained from different providers (Japan Energy) according to the above method of the present invention. In this case, the Applicant added to the CdTe polycrystal a very small amount,
0.052 ppmw of Se was detected.

Further, as shown below, B is not taken in the vapor phase growth method. G. FIG. W. Blackmo
re, et al., "Boron segmentation in
Czochralski-Ground CdTe "
J. of Crystal Grwoth, pp. 3
35-340, Vol. 8 (1987), by using the B ₂ O ₃ encapsulant grown by liquid encapsulated Czochralski method C
Chemical analysis of the dTe ingot showed that the material was 90 ppm
a containing boron or less, indicating that the boron distribution is non-uniform. The authors note that observations of low carrier concentration and high electrical mobility in this material also support the theory that most of boron is not electrically active. In this paper, the concentration is
pm "ppma".

The polycrystalline CdTe obtained in Example 1 according to the present invention has a boron concentration of 3.4 ppmw,
This corresponds to 5.48 ppma. The conversion formula is 1 ppma =
M (CdTe) / M (B) × 1 ppmw = 240/1
0.81 ppmw = 22.2 ppmw (where M (Cd
Te) is the formula weight of CdTe and M (B) is the atomic weight of boron).

Applicants have acknowledged that the boron concentration of the material analyzed in the article is higher than that of the sample synthesized according to the invention. Other detected impurities (N
a, Mg, Al, Si, P, S, Cl, K, Ca, C
r, Mn, Fe, Co, Ni, Cu, Zn, As, M
For o), the amounts found in the compounds prepared by the method and apparatus of the present invention are all commercially available E
Substantially lower than in SPI products.

According to the analysis results shown in Table 1, ESP
The polycrystalline compound obtained from I has a purity corresponding to 99.98%, ie a purity of about 4N. But,
The polycrystalline compound produced by the method and apparatus of the present invention has a purity corresponding to 99.9997%, ie, 5%.
It has a higher purity than N.

The synthetic method described is comparable to any growth method. The apparatus and growth methods described in the following examples are illustrative and are particularly advantageous for use in practicing the present invention.

Example 1A Applicants have synthesized a CdZnTe alloy (Group II-II-VI) having a Zn content of 20%. Zn is T _m = 41
It has a melting point of 9.5 ° C.

In the first step of the preferred method, the preparation of the packing material, stoichiometric amounts of the reactants Cd, Zn, Te,
That is, 139.37 g of Cd and 20.27 g of Zn
And 197.78 g of Te were placed in crucible 18.

The filling material has a total weight of 357.42 g. Approximately 30 g of B ₂ O ₃ mounting medium pellet 30 was placed on top of the reactants. The reactants occupied the lower region D of the crucible 18.

The receiver 20 containing the heating element 32 was placed on the pellet of the encapsulant 30. The heating element 32 consisted of about 60 g of liquid gallium. The mounting medium 30 and the receiver 20 occupied the upper region U of the crucible 18.

The synthesis process was carried out in a manner similar to that described in detail in Example 1 with reference to FIGS.
Method parameters (temperature, time, pressure, etc.) were employed according to known techniques.

In order to avoid segregation of Zn, the heating coil 1
4, by reducing the power of the first container 16 at the same time, as shown in FIG.
Cooling was performed.

When the system returned to room temperature, the crucible 18 was removed from the chamber 12. Again, Applicants did not observe any condensation of reactants on the walls of chamber 12. This indicates that no gas reactant escaped from the encapsulant 30 during the process. Further proof of this was obtained by weighing the synthesized CdZnTe compound, which did not show any significant reduction in weight relative to the initial amount of reactants.

Example 2 Applicants have grown two CdTe single crystals from a polycrystalline compound synthesized by the method and apparatus of the present invention.
Both crystals (Crystal 1 and Crystal 2) were purchased from Yellin,
N. And the article by Szapiro, S .; ,
“Vapor Transport of Nonst
oichiometric CdTe in Clos
ed Ampoules ", J. of Crystal
Growth , Vol. 555
The PVT was grown by the PVT (Physical Vapor Transfer) method described in No. 60. As shown in FIG. 5, 10-20 g of polycrystalline CdT prepared by the method and apparatus described in Example 1.
e34, a quartz ampoule 36 connected to a pull rod 38
Placed inside and sealed with a vacuum greater than 10 ^-5 mbar. Then, a quartz ampoule 36 containing polycrystalline CdTe 34 was placed inside a vertical furnace (not shown) having a temperature distribution of the type shown in FIG. The quartz ampoule 36, which was initially placed in a furnace having a temperature distribution as shown in the figure, was moved upward by a pull rod 38 with respect to the furnace. Thus, solid phase condensation only occurs if the pressure in the ampoule does not impede mass transfer due to supersaturation of the Cd and Te vapors. Table 2 shows the boron concentration values measured in the synthesized polycrystalline sample and in the two crystals grown by the described gas phase method. B
The value of (the main impurity in the polycrystal) is reduced by half of the size of the crystal grown in the vapor phase, indicating that B is not taken in in the vapor phase growth. The crystals thus obtained had a purity of 6 / 7N.

[0126]

[Table 2]

As noted in Yellin and Szapiro, p. 556, if the stoichiometry of the polycrystalline filler shifts toward Cd at a rate greater than 0.01 mole%, the material Transport growth is completely prevented and if the stoichiometric ratio of the polycrystalline filler is 0.5.
If it shifts toward tellurium at a rate greater than 04 mol%, the growth rate will decrease significantly. Repeated laboratory chamber tests have demonstrated that the polycrystalline CdTe compound synthesized by the method and apparatus of the present invention allows mass transfer growth in a sealed ampoule, so that the polycrystalline CdTe compound , Which have somewhat lower stoichiometric shifts than these levels.

Applicants have noted that other polycrystalline compounds synthesized by the methods and apparatus of the present invention also have low stoichiometric shifts (eg, exact stoichiometric ratios), which indicates that the reactants are significantly Due to the fact that it can be encapsulated before reaching the temperature at which significant vaporization takes place.

Example 3 FIG. 7 allows the synthesis of polycrystalline compounds in a manner similar to that described with reference to FIG. 1 and the growth of single crystals in the next step by the vertical Bridgman method. The following shows an apparatus for causing this.

The container 16 and the flat-bottom quartz crucible 18 of FIG.
A crucible 40 and a container 42 centered on a housing or pocket 46 in which a seed single crystal 44 of a substance to be synthesized and grown (eg, CdTe) can be placed.
And can be replaced.

Once the encapsulant (eg, B ₂ O ₃ ) 30 has melted, the crucible 40 is charged with the reactants (eg, Cd26 and Td26).
e28) is raised as shown in FIG. 2 to melt and obtain the reaction product as described in Example 1. Up to this point, CdTe seed 44 remains solid because the melting point of CdTe is higher than the reaction temperature. Next, the temperature is increased to melt CdTe. At this stage, heating should be performed so that the introduced CdTe species 44 does not completely melt. This is done using moderately sized and / or arranged induction heating coils 14 and in the polycrystalline melting stage (FIG. 4, lm, mn).
This is possible by controlling the heating gradient during. Growth then occurs as in a typical vertical Bridgman method.

The seed crystal 44 produces a lattice structure in which the molten compound can grow during the proper cooling realized by lowering the crucible 40 by moving the container 42. During cooling, the seed crystal 44 and the grown crystal are at a temperature below the corresponding melting point, while the growing compound above remains molten.

Appropriate thermal gradients and growth times will be apparent to those skilled in the art. An additional heating element of suitable shape can be introduced around the crucible 40 to obtain a suitable temperature distribution.

Example 4 FIG. 8 shows that a polycrystalline compound according to another embodiment of the present invention can be synthesized by a method similar to that described in Example 1, and a single crystal is grown by the Czochralski method. The following shows an apparatus for causing this. To this end, the receiver 20 of FIG.
To a graphite ring 3 having an outer diameter similar to the outer diameter of the receiver 20, ie, 3.5 cm, and an inner diameter greater than or equal to the desired single crystal diameter (eg, 2.5 cm).
2 and can be replaced. The annulus can be mounted so that it floats on the surface of B ₂ O ₃ but does not rotate with respect to crucible 18.

Then, the synthesis proceeds according to the method outlined in Example 1, except that heat is induced in B ₂ O ₃ by the graphite ring 32. Synthesis occurs and C in the crucible
Once the dTe has melted, growth can be achieved by the Czochralski method, for example, by maintaining the liquid CdTe at an appropriate temperature and securely attaching the seed single crystal 44 to a movable rod 48 located at the top of the furnace 10. Happens immediately. Growth proceeds by plunging the rod through the holes in the graphite ring 32 into the liquid compound and slowly lifting the seed from the molten mixture.

The apparatus of FIGS. 7 and 8 can include a suitable shielding member located in the crucible to change the temperature gradient in the region of the growth interface. Suitable shielding members for use in the device are described, for example, in EP 509,31.
No. 2 is described in FIGS. 5 and 6. For example, this member in the form of a ring blocks the radiation generated by the heating coil and gives the filling material the correct thermal gradient.

In particular, the present invention offers numerous advantages for crystal synthesis and growth. These advantages include that the described method and apparatus ensure complete reaction of the components and accurate stoichiometry. Furthermore, according to the present method, there is no limit on the amount of product, no vapor loss,
Use equipment that is safe (Cd and Te can cause cancer), has short synthesis times, and is simple.

The above description of the preferred embodiments of the present invention
Although illustrated and described, it is not intended to be exhaustive or to limit the invention to the form disclosed. Modifications and variations are possible in light of the above teachings or may be acquired from practicing the invention. The description includes specific data values obtained through experimentation. These values serve only as examples, and the true scope of the invention is only defined by the claims and their equivalents.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of an apparatus used to synthesize a polycrystalline compound, consistent with an embodiment of the present invention, showing a stage before the encapsulant melts.

FIG. 2 is a cross-sectional view similar to FIG. 1, showing the stage after the encapsulant has melted and surrounded the reactants.

FIG. 3 is a cross-sectional view similar to FIG. 2, showing the stage after the encapsulated reactants have melted.

FIG. 4 is a graph showing heating coil power versus time for CdTe during the practice of the method of the present invention.

FIG. 5 is a cross-sectional view of a conventional apparatus for growing a single crystal hermetically sealed ampoule PVT.

FIG. 6 is a graph showing a typical heat distribution of a furnace for PVT growth of a single crystal.

FIG. 7 is a cross-sectional view similar to that of FIG. 1 of another embodiment of the present invention, showing an improved vessel having a seed pocket at the bottom below the reactants.

FIG. 8 is a cross-sectional view similar to FIG. 1 of another embodiment of the present invention, showing a rod placed on a container for inserting seed crystals into an encapsulated melt.

 ──────────────────────────────────────────────────の Continued on the front page (71) Applicant 591011856 Pirelli Cavies System e. p. A (72) Inventor Minchen-cha I-43100 Parma, Via Solari 30 (72) Inventor Tamash Guereg Hungary Har-2000 Sentendre, Berch Utocha 18 (72) Inventor Giovanni Zuccari Italy 43058 Sol Boro, Piazzale Marchesi Rattetta, Republic of Parma 10 (72) Inventor Andrea Zappettini I-42100 Reggio Emilia, Via Ci Pisacanne, Italy 9

Claims (20)

[Claims] 1. A method for producing a high purity and accurate stoichiometric Group II-VI or III-V polycrystalline compound comprising the steps of: a) encapsulating agent with said encapsulation Heating to a first temperature sufficient to melt the agent; b) surrounding a stoichiometric amount of at least two reactants with the encapsulant in a molten state (during encapsulation, the reactants are Not reaching a temperature sufficient to cause one or more to evaporate); and c) forming a polycrystalline Group II-VI or Group III-V compound. 2. The step (b) further comprises the step of: reacting the reactant surrounded by the encapsulant with a second sufficient to melt the reactants and react the reactants with each other to form a reaction product. Heating to a temperature; and heating the reaction product to a third temperature sufficient to melt the reaction product and for a time sufficient to synthesize and homogenize the reaction product. The method of claim 1. 3. A method for producing a high purity and accurate stoichiometric polycrystalline compound comprising the steps of: a) placing a stoichiometric amount of at least two reactants in a first zone; b) placing a sufficient amount of encapsulant in the second region when the encapsulant is in a molten state (the second region is to the first region of the encapsulant in a molten state) to completely surround the reactants; C) creating a gas atmosphere around said first and second regions, wherein said first and second regions are heated separately from each other at a selected maximum operating temperature.
Pressurizing to a pressure substantially above the vapor pressure of most of the volatiles of the reactants; d) a first temperature sufficient to melt the encapsulant in the second region without heating the first region. (The first region is maintained at a temperature sufficient to avoid vaporization of the reactants, thereby causing the encapsulant to move from the second region to the first region in a molten state and reacting E) heating the reactants surrounded by the encapsulant to a second temperature sufficient to cause the reactants to melt and react with each other to form a reaction product. And f) heating the reaction product to a third temperature sufficient to melt the reaction product and for a time sufficient to synthesize and homogenize the reaction product. 4. A method for producing a high purity and accurate stoichiometric polycrystalline compound comprising the steps of: a) placing a stoichiometric amount of at least two reactants in a first region of a vessel; B) placing an amount of encapsulant sufficient to completely surround the reactants in the second region of the container when the encapsulant is in the molten state (where the second region is the encapsulation in the molten state); Suitable for transfer of an agent to said first region, said second region being directly adjacent to said first region, said first and second regions may be heated separately from each other); c) said Placing the vessel in a sealed, vertically arranged chamber; d) creating a gas atmosphere around the vessel, wherein the atmosphere is substantially free of most of the volatiles of the reactants at the selected maximum operating temperature. Pressurizing to a pressure above the vapor pressure; e) encapsulating said second region Is heated to a first temperature sufficient to melt, while maintaining the first region at a temperature sufficient to avoid vaporization of the reactants, whereby the encapsulant is melted from the second region. Moving to the first region to surround the reactants; f) melting the reactants surrounded by the encapsulant, wherein the reactants melt and react with each other to form a reaction product. Heating the reaction product to a third temperature sufficient to melt the reaction product and for a time sufficient to synthesize and homogenize the reaction product; and g) Heat. 5. The method of claim 4, further comprising, after step (g), h) bringing the reaction product surrounded by the encapsulant below the melting point of the reaction product. Cooling to a temperature but above the melting point of the encapsulant; and i) separating the reaction product from the encapsulant. 6. The method of claim 4, wherein the reactants comprise at least one Group II element and at least one Group VI element. 7. The method according to claim 1, wherein the reactant is at least one III
5. The method of claim 4, comprising a Group V element and at least one Group V element. 8. The method of claim 6, wherein said reactants are Cd and Te. 9. A polycrystalline compound produced by the method according to claim 4. 10. The polycrystalline compound of claim 9, wherein the compound has a purity of at least about 5N. 11. A method for producing a single crystal of high purity and precise stoichiometry from a polycrystalline compound produced by the method of claim 4, further comprising the following steps:
Placing the seed single crystal in the housing in the first region of the container; performing steps (a)-(g); and gradually lowering the container relative to the chamber, thereby reducing the temperature of the first region. Is gradually reduced to grow the single crystal. 12. A method of producing an encapsulated reactant composition comprising the steps of: a) heating an encapsulant to a first temperature sufficient to melt said encapsulant; and b) chemical A stoichiometric amount of at least two reactants is surrounded by the encapsulant in the molten state before the reactants reach a temperature sufficient to cause vaporization of one or more of the reactants (the reaction The body comprises at least one Group II element and at least one Group VI element). 13. The composition comprising at least one Group II element and at least one Group VI element, having a purity of at least about 99.998%, and wherein any of the elements comprising the compound is at least about 0.1%. A polycrystalline compound in which no more than 01 mol% does not deviate from the stoichiometric composition. 14. An element comprising at least one Group III element and at least one Group V element, having a purity of at least about 99.998%, and wherein any of the elements comprising said compound are at least about 0.9%. A polycrystalline compound in which no more than 01 mol% does not deviate from the stoichiometric composition. 15. A method of producing a single crystal of high purity and precise stoichiometry comprising the steps of: a) heating the encapsulant to a first temperature sufficient to melt the encapsulant. B) combining a stoichiometric amount of at least two reactants with the encapsulant in a molten state before the reactants have reached a temperature sufficient to cause vaporization of one or more of the reactants; A box (the reactants comprise at least one Group II element and at least one Group VI element); c) melting the reactants surrounded by the encapsulant; Heating the reactants to a second temperature sufficient to react with each other to form a reaction product; d) bringing the reaction product to a third temperature sufficient to melt the reaction product; Heating for a time sufficient for the product to synthesize and homogenize; and e) From serial reaction product to form a single crystal. 16. A method for producing a single crystal of high purity and precise stoichiometry comprising the steps of:
Producing an encapsulated reaction product according to the method of claim 1; heating the reaction product to a molten state; inserting a seed single crystal into the reaction product; and melting the seed single crystal into the molten reaction product Gradually raise from. 17. A single crystalline compound comprising at least one Group II element and at least one Group VI element and having a purity of at least about 99.9998%. 18. A single crystalline compound comprising at least one Group III element and at least one Group V element and having a purity of at least about 99.9998%. 19. An apparatus for producing a polycrystalline compound having high purity and accurate stoichiometry comprising: a furnace having at least one chamber; a first for containing a reactant. A container in the chamber having a region and at least a second region for containing an encapsulant and a heater for the encapsulant; means for rotatably and vertically supporting and moving the container in the chamber And independent heaters for the first and second regions of the vessel. 20. An apparatus for producing a polycrystalline compound having high purity and accurate stoichiometry comprising: a furnace having at least one vertically arranged chamber; containing a reactant A container in the chamber having a first region for receiving the encapsulant and a heating element for heating the encapsulant immediately above the first region; and the chamber; A member connected to a motor for rotatably and vertically supporting and moving the container therein; and without heating the first region of the container when surrounding the second region of the container. An induction heating coil for inducing a current in the heating element and for inducing a current in the reactant when surrounding the first region of the vessel.