DE2422251A1 - METHOD AND APPARATUS FOR MANUFACTURING DOPED CADMIUM TELLURIDE CRYSTALS - Google Patents

Description

PAT E N TAN WA LT

DR. HANS ULRiOH MAY

D S MÖNCHEN 2, OTTOSTRASSE 1a TELEGRAM: MAYPATENT MUNICH

TELEPHONE (OStO 593682 2422251

CP 482/1274 Munich, May 8, 1974

"B 4 ^ 01.3 PB. Dr.M./cs

Commissariat ä 1 * Energie Atomique in Paris / France

Method and device for the production of doped cad "

Hiium telluride crystals

The invention relates to a method and a device for manufacturing of doped cadmium telluride.

It is known that when using single crystals of semiconductors, like germanium or silicon as detectors, these semiconductors, which show intrinsic conductivity in the pure state, either in the pure state State or doped.

In applications where one is dealing with a semiconductor with a high specificity Resistance must work, such as in solid-state ionization chambers, it is advantageous to use semiconductors with a high atomic weight · For example, detectors are used to detect gamma rays with a high atomic weight more sensitive, since the effective absorption cross-section for gamma rays is proportional to the atomic weight of the the connection forming the detector. In order to produce semiconductors with a high atomic weight, two elements with a high Combine atomic weight, their valence electrons in their cheadian Lead connection to the formation of a semiconductor crystal. There is

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several possibilities of such combinations, such as gallium arsenide or cadraium telluride. Cadmium telluride is the better detector because its atomic weight is higher. Tellurium crystallizes vie cadmium cubic system. The number of electrons in the outer shell 0 is two for cadmium and six for tellurium, so a total of eight for cadmium telluride, which corresponds to the stable outer electron shell of xenon. Of its perfect and cadmium telluride, without contamination and without dopant with an exactly equal number of Cadraiumatomen and tellurium _t is denoted by itself a semiconductor with high resistivity, sometimes referred to as ^w * seinüsolator. When the tellurium in excess of the cadmium is present, is an excess of holes and thus with one of its components "doped ¹¹ semiconductor before, in this case, a semiconductor of the type P is Likewise, if the cadmium is present in a slight excess, a N-type semiconductors.

You can also use a cadmium telluride crystal with a doping a donor or acceptor to form a P-type semiconductor or N to obtain. or also to dose the doping agent in such a way that its concentration compensates for the excess of one of the ingredients. In the case of a semiconductor, cadmium telluride, initially as a result of If an excess of cadmium is of type K, indium can be used, for example add with the valence 1 and so intercept the moving electrons and a semiconductor with high specific resistance

Solid «

produce. In the . '• ionization chambers, where a semiconductor single crystal is arranged in a sandwich between two electrodes, using a semiconductor having a high specific gravity and high resistivity without crystal defects, so that the leakage "··

do
electricity / is too substantial and is under the influence for example

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certain gamma rays form pairs of electron-iiocfe, vas leads to a change in the current between the electrodes, provided that the semiconductor is sufficiently good that the pair Electron hole not by recombination in its migration is destroyed by the crystal. The difficulty is to find such a substance with low impurities, one that is strictly adhered to stoechiometric composition or a precisely defined doping and with a crystal lattice without twinning and create disturbances. Once made, such detectors work at room temperature, as opposed to the currently used detectors is an advantage, since the lithium doped germanium detectors at low temperature must be operated. The detectors made of lithium doped germanium, where one finds the impurities in the germanium caused by lithium compensated to obtain a semiconductor are inevitably less advantageous than the cadmium telluride detectors in other respects too, since the capture cross-section for gamma rays is proportional to the atomic weight of that used for detection, for example Semiconductor is.

The invention now aims at a method for producing doped cadmium telluride, which is used as a radiation detector at room temperature can be used. The process according to the invention is characterized in that three crystallization operations are carried out in succession in the presence of a controlled dose of dopants. In a first stage, one synthesizes from pure cadmium and pure tellurium in the stoechiometric components an imperfect one Cadmium telluride bar »In the second stage, this Ingots at a temperature in the middle of the melt stGechiomatrisclj.en mixture tellurium-fiaamivni melted, 12m one

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to obtain a purer crystal which, however, still has numerous defects, both impurities and crystallization defects. In Finally, in the third stage, this crystal is melted and from a tellurium solution at a melting temperature near that recrystallized from pure tellurium, which finally results in a doped cadmium telluride single crystal without impurities and with a very low degree of imperfections, twinning and others Errors received.

Purpose of the invention is the production of a single crystal doped cadmium telluride whose doping is accurately controlled, either for manufacturing a semiconductor of a certain type with a certain specific resistance or to compensate for the excess of one of the components by introducing an appropriate dopant ma a crystal having to obtain high resistivity.

In other words, according to the invention, a rough synthesis is first carried out in a first stage. Then, by heating to about 1090 ° C, “what is the melting temperature of the? stoechiometric mixture corresponds »and cooling a second ingot made of polycrystals of cadmium telluride. The subsequent production of the single crystal at low temperature yields a crystal with a very low proportion of faults and little fÜkro-Aus £ älungen _p which does not apply to the crystals produced at high temperature. The crystals obtained at low temperature are suitable on their own as detectors for nuclear purposes.

The basic materials are cleaned separately before starting the first synthesis of cadmium telluride. In the process according to the invention, this synthesis takes place in a closed vessel, where the

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Batch is prepared by weighing _? to achieve a composition close to the stoechiometric composition. The ingot obtained after melting and cooling is freed from its upper part containing the void, then stripped and rinsed. The cadmium and tellurium are made before the first synthesis. Zone melting cleaned and then filtered under a hydrogen atmosphere * to remove every trace of oxide. The first synthesis is preferably carried out in one. Test tube made of resin without content of OH ions ₉ which has an inner lining made of graphite. This coating is obtained by cracking methane, benzene or another carbon-rich substance in a vacuum between 1000 and 1200 ⁰ C. Kack the filling, the test tube is sealed in an ultra-vacuum and introduced into a tilting furnace, so that the synthesis in a horizontal position ^ nd the subsequent Cooling can take place in a vertical position, whereby the cooling is carried out slowly on one side from the bottom of the test tube.

In a modified embodiment of the invention, a batch is introduced into the closed test tube where the first synthesis takes place, the composition of which deviates slightly from the stoechiorometric composition due to a slight excess of tellurium. The setting of this deviation with regard to the stoechiometric composition determines the choice and necessary concentration of the dopant.

In the method according to the invention, after the first synthesis, a Crystallization at a high temperature close to the melting temperature the stoechiometric mixture in, one under Oltrava

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sealed container. which is heated in buckets furnace, pre »nonrnien, In a first embodiment of the erfindungsgeraäßen method, this vessel is a graphitized test tube is equal to the-used in the first synthesis, the so close under ultra vacuum h is closed at äem material after a übsr-scimS has added ti.mmngsmiit.eln additional tellurium containing Do- _ff if it is necessary for the third crystallization under the conditions shown below "

As can be seen from FIG. 1, which is explained in more detail below, the fluctuations are relevant to the stoechiometric composition. can crystallize within which the plate and cadmium, in üer order of 10 "Atoiuen / enr at about 900 ° Co However, such a fibarschuß gemlgt on one of the components to be ;, drop sufficient to dan spesif'ischen resistance,

Plague body that the ye ^ fendwng of such a crystal in a -loni-

* These distances not komt in question of the concentration with respect to the stoechiontetrischen concentration, however, correspond to animal magnitude of the concentration of dopants * the isan ± n the crystal lattice of the signature fcannj to the excess of one of the components to compensate for and to a higher resistivity of at least to * ⁵ ohms / cm backsukoiamen «

One generally works with an excess of tellurium, since the slope of the equidus curve in FIG. 1, which indicates the concentration of the liquid as a function of temperature, is steeper on the tellurium side than on the cadmium side and consequently the concentrations by adjusting the temperature can be better controlled ^ and partly because the knowledge of the öfesrsolmssss the concentration of tellurium the & s? t the einzufüh · =

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n-type botany is determined.

In a modified embodiment, the crystallization takes place at a high temperature, i.e. a temperature close to the melting temperature of the stoechiometric mixture of tellurium and cadmium in a sealed test tube made of quartz with a graphite coating carried out and the partial pressure of a component regulated by adjusting the temperature of a part of the test tube » where a crucible is located “that contains at least one of the substances whose partial pressure should be kept constant

In a modified embodiment of the invention, a pure component, the cadmium or tellurium, is poured into the crucible contained in the test tube and the temperature of the crucible, which _{is labeled T 2} , is kept lower than the temperature T _{1 of} the melt during crystallization. In a second modification of the invention, in addition to one of the two components cadmium or tellurium, a volatile dopant is added to the crucible. To the partial pressure of one of the components of the glass above de? To adjust the melt, the atomic absorption of the light is measured and, according to the measurement result, the temperature T ₂ is adjusted by a known type of control device so that the partial pressure in the gas remains at the desired value.

According to a further modification of the method according to the invention, the substance placed in the crucible is dissolved in a slightly volatile amphoteric solvent, the introduction of which into the crystal does not change its electrical properties. In this case, the temperature T _{2 of} the crucible is kept equal to that of the melt during the crystallization, which is what the furnace construction and

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Procedure simplified The Fartialdrucli of the component i is determined by the following formula:

^p i ^sp i ' ^x i * ^Y i
where P? Vapor pressure of the pure component i at the temperature

V. - ■

X. the mole fraction of component i,

Y .. the thermodynamic activity coefficient of component i at temperature T ₁ and concentration X., For example, binary alloys of cadmium with tin, indium, gallium _f zinc or binary alloys of tellurium with tin, indium, gallium and zinc ₀ or also cadmium halides,

In all modifications of the invention, the crystallization is at high temperature achieved by relative displacement of the test tube and the temperature gradient of the furnace. The test tube can be rotated continuously or continuously or made to vibrate by means of a corresponding drive system. This method

in the direction perpendicular to the solidification front of the so-called normal cooling / leads to a deposition of the Impurities at the top of the billet.

During the last crystallization of the process described above, the crystal is dissolved and then as a single crystal at deeper Temperature, i.e. a temperature close to the melting point of pure tellurium crystallizes.

In a first modification of the production of single crystals at low temperature, the "solution exhaustion" process, the ingot with a very large excess of tellurium is introduced into a quartz test tube, which is optionally coated with graphite ₅ with the relative concentrations of cadmium and tellurium These are selected: c. the temperature in the range of about 900 ° C _;

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what is close to the melting point of pure tellurium is completely liquid. The test tube is placed under ultra vacuum or under the Partial pressure of a neutral or reducing gas tightly closed. The dopant is added to the batch and the crystallization is carried out in a vertical oven above for crystallization described at high temperature, performed after the test tube is sealed as close as possible to the material was «The difference is that the temperature of crystallization in the presence of the solvent tellurium is much lower than that which would correspond to the stoechiometric mixture.

In a modification of the doping process, the dopant is introduced into a crucible suspended in a test tube, either pure or dissolved in an amphoteric solvent ₉ and the partial pressure of the dopant is regulated at high temperature as in the case of crystal!

In a second modification of the production of single crystals at low temperature, a zone of the doped liquid tellurium is shifted through the original crystal so that the solubility limit of the dopant in the tellurium solvent is not exceeded. To choose a crystal, which was doped at the crystallization at high temperature with the same dopant to hold _a to the concentration of the latter in the solvent zone in accordance with the Port below constant, and to achieve that if the solubility limit of the dopant is exceeded in the solvent zone As can be the case for cadmium chloride in tellurium, the concentration of dopant remains constant without the crystal coming from the crystallization at high temperature, which is not doped in this pail, being selected

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is, must pre-dop. According to the principle, the production of the single crystal is carried out in a quartz test tube with a graphite coating at ultra- high temperatures, with the temperature in the test tube being changed between 500 and 900 ° C with high temperature gradients of the order of 13 ° C / cm «

According to the invention, instead of working in a vacuum or ultra-vacuum at least one of the three described KJ crystallizations in one Make an inert gas atmosphere.

The invention also relates to an implementation device of the method according to the invention, which is characterized by

- Devices for cleaning the cadmium and tellurium by zone melting!

- Devices for filtering cadmium and tellurium under water toffatmosphärej

- Vessels in which the mixture of cadmium and tellurium is a first Is subjected to crystallization j

- a tilting furnace to carry out the synthesis in a horizontal position and cooling down in a vertical position?

- ovens for carrying out the crystallizations at high and low Temperature;

- Test tubes, which contain crucibles, into which you can put the ingredients can give whose vapor partial pressure are kept constant target?

- Devices for measuring the atomic absorption of light in the gas phase above the melt pool}

- Devices for controlling the temperature T _s in accordance with the concentration of the gas phase on the desired component;

- Devices for carrying out the single crystal production Shifting a zone of the solvent, which in turn

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point:

an oven with a heating ring, which allows the test tube 9 in which the crystallization takes place to be heated over a small part of its height \

mechanical devices to hold the test tube vertically and to rotate continuously about a vertical axis.

To carry out the method according to the invention, one uses an arrangement of oven test tubes that can be tilted around to maintain contact between the liquid and the ingot and to drive out gas bubbles between the liquid on the test tube wall and the ingot on the side, so that through this device a more uniform crystallization is achieved.

The invention is illustrated by the following description of a embodiment given as an example only. The description refers to the attached drawings. Show here:

1 shows the liquidus-solidus curves of the cadmium-tellurium mixture;

- _o Figure 2 schematically shows the tube used for the crystallization at high temperature;

- Fig. 3 schematically the heating ring und.das test tube, which for

Crystallization in tellurium solvent at low temperature is used

₀ 4 schematically shows the device for crystallization at low temperature using an inclined test tube which is rotated continuously.

As indicated above, the method _{according to the invention consists in 9} at a high temperature in the vicinity of the melting temperature of the stoechiometric mixture of tellurium-cadmium polycrystals of doped cadmium telluride with a certain stoechiometric difference.

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«, -.» - 2A222S1

chiang manufacture. This is followed by a single crystal division, which provides crystals which have a very low level of imperfections and little microprecipitation, which is not This is the case for crystals produced at high temperature. The specific one Resistance of the crystals is determined by doping the product with halogens, for example in the form of cadmium chloride, cadmium fluoride, -iodide "-bromide set, with the dopant in the tellurium zone is introduced »One can also use indium, tin, etc., =

What is new about the process is that the cleaning and crystallization operations are carried out one after the other in a logical sequence be., so that you get a material with high resistivity obtained whose properties in both crystallographic and are also better in electrical terms.

1 shows the solidus-liquidus equilibrium curves as a function of temperature (ordinate) and the relative concentrations of tellurium and cadmium, with the concentration of tellurium increasing on the abscissa from 0 on the left to 1 on the right the solidus curve is denoted by S »The so-called high temperature crystallization takes place at a temperature close to point A _8, which corresponds to the melting temperature of the stoechiometric mixture of cadmium tellurium. If one starts from a point B, which corresponds to the temperature T i, the concentration of the crystallizing solid lies at point C of the solidus curve S, for which the concentration D results from the figure. The Einkristallherstellung at low temperature occurs at a point E, corresponding to a concentration of tellurium Holien ο The concentration of the obtained by crystallization at this temperature the solid product is de ?? Figure at point F "

■ 409848/1008

The "belly" of the solid curve is in this figure, which is not to scale exaggerated. The distance to the stoechiometric composition

17 j 3

the solid mixture never exceeds about 10 atoms / cm.

In Pig «2 the test tube 2 is shown on the left, in which the crystallization is carried out at high temperature and which is moved at a speed V in the direction of the arrow downwards. The temperature of the furnace ± n as a function of the ordinate is shown in curve 4, namely the changes in temperature as the ordinate as a function of location x. The furnace has three temperature zones, where the temperature in area 6 _{corresponds to a temperature above the melting temperature of the stoechiometric mixture and temperature T 2} in area 8 corresponds to a lower temperature which is used to set the partial pressure of one of the components in the crucible 10 in the test tube is located, serves. The temperature T ₃ in the area 12 to which the test tube is fed »is below the melting temperature» the liquid 9 crystallizes to form a solid 11,

In FIG. 3, the test tube is shown on the left, where crystallization takes place at low temperature. This test tube is moved downwards at speed V and is surrounded by a heating ring 13, which generates temperature gradients, the values of which are given in curve 14 as changes in temperature as a function of the location χ When the test tube is lowered, ie when passing through through the heating ring, the crystal passes through a zone of liquid doped tellurium 16, and the crystal dissolved at 18 crystallizes again at 19 _$ , the first crystallization starting from a nucleus 20-

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In a modification of the method shown in Pig, 4 the Test tube moved in the direction of arrow V and rotated continuously in the direction of arrow 22. The raw material 23 passes through the zone of liquid doped tellurium 24 lying in the region of the hot ring 26 and crystallizes again at 28 with formation of the finished single crystal.

In a first example the production of cadraium telluride will be used Rods of tellurium and cadmium each 1500 g and 500 mm in length initially purified by zone melting. To do this, they are placed in quartz test tubes in a hydrogen atmosphere and then into a Oven set. For the purpose of cleaning, the zone melting takes place in twelve passes at 25 mm / hour. The cleaned metals will be then for synthesis with a small excess of tellurium in brought a horizontally held test tube. The temperature is increased by only 12 ° C per hour, thus causing the very exothermic formation reaction doesn't happen all of a sudden. The temperature is then held at 1200 ° C. for two hours and then brought Place the test tube in an upright position and cool within 12 hours, with the cooling beginning at the bottom of the test tube and the The oven used is, for example, an oven with heating rings.

During the second stage, ie the crystallization at high temperature, a small excess of tellurium is added to the test tube containing the alloy previously obtained and the temperature of the test tube is increased to 115O ° C. in order to melt the ingot. The test tube containing the molten material is then displaced downwardly _s where a temperature of 1O9O ° C prevails, to cause crystallization. The lowering speed is 5mm / h.

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In the third stage, ie the KristalliEaticn "at deep?" Temperature "is given to the ingot into a test tube made of quartz were introduced into the above 60 g tellurium containing 700 ppm of cadmium chloride. The tube is slowly moved at a speed of O ₈ 3 mm / hr. Downwardly, whereby it with At this temperature and lowering speed, the temperature of the solid-plush interfaces is 660 ° C. This method gives an ingot of qadmium telluride doped with about 3 ppm of cadmium chloride.

In a second example, the first bar is produced as in the example above. Crystallization at high temperature takes place by introducing the alloy of cadmium telluride into a test tube “ which is provided with a crucible in its upper part. This crucible contains pure tellurium and about 300 ppm cadmium chloride. The lower part of the furnace is heated to 1130 ° C and the test tube is then lowered. At ⁰ C 1QOO the doped with 3 ppm of cadmium chloride, cadmium telluride crystallized. The temperature of the upper part of the test tube, where the crucible is located, must ^{remain at about 900 °} C. The crystallization at low temperature takes place as in Example 1 _s, except that the 60 g of tellurium doped with 700 ppm of cadmium chloride is replaced by 60 g with only 200 ppm cadmium chloride doped tellurium replaced * The single crystal obtained is similar to that obtained in Example 1.

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Apart from the solid-state ionization chambers, monocrystals of cadmium telluride have numerous other uses, of which
Examples include: detectors for nuclear rays or infrared of the "Photon Drag" type, electro-optical modulators, infrared-permeable windows, active components such as diodes or photodiodes, high-temperature optocouplers (photocoupleurs), bipolar transistors, field-effect transistors, junction transistors and those with an insulated gate electrode , Thyristors, diacs, triacs and lasers
and electroluminescent cells.

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Claims (1)

Claims 1. Process for the production of doped cadmium telluride single crystals without impurities and with a small proportion of disturbances, twinning and other errors, characterized by this that three crystallization operations are carried out one after the other, namely one first operation from pure cadmium and pure tellurium in stoechiometric proportions an imperfect ingot of cadmium telluride is synthesized will; In a second operation, the previously obtained ingot is melted and recrystallized at a temperature close to the melting temperature of the stoechiometric mixture tellurium-cadmium _{8 in} order to obtain a purer crystal, which, however, still has numerous defects both in terms of impurities and crystalline and finally, in a third operation, the crystal obtained is melted and recrystallized from a solution of doped tellurium at a melting temperature close to the melting temperature of pure tellurium »which finally results in a single crystal of doped cadmium telluride, with at least the third operation is carried out in the presence of a regulated amount of dopants * 2. The method according to claim 1 "characterized in" that the starting materials of cadmium and tellurium are purified separately before the first operation, and the synthesis of the first working operation is carried out in a closed vessel, the batch is prepared by weighing _s · so as to close a composition in the stoechiometric composition, and that the after the melting 409848/1008 zen and cooling in the first step obtained ingot is freed from its upper part containing the blowholes, stripped and rinsed. 3. The method according to claim 2 _S, characterized “ that the cadmium and tellurium cleaned by zone melting before the first step and before that filtered under a hydrogen atmosphere to remove traces of oxide and the first step in a quartz vessel without content of OH ions, the inside by cracking a carbon-rich substance »v / ie benzene or methane _g in vacuo 1000-1200 ⁰ C provided with a graphite inner layer wurdej is performed * after the vessel filled with the starting materials was sealed in the ultra-vacuum and used in a tilting furnace, wherein the synthesis in a horizontal Position and the cooling take place in the vertical position of the vessel and the cooling is carried out slowly in one direction starting from the bottom of the vessel ₈ and that the pickling takes place after cooling using bromine alcohol. 4. The method according to any one of claims 1 to 3 _9, characterized in that given a for the first operation (synthesis) batch intended for the first operation (synthesis) in a closed vessel and the composition of the batch is slightly removed from the stoechiometric composition by adding a small excess of tellurium. 5 * A method according to any one of claims 1 to 4 »characterized in that after the first operation, the second operation at a high temperature near the melting temperature of de ^ toechiometrisehen mixture inside a sealed under ultra vacuum vessel _ff which is heated in a furnace _c performed will. 40 9 8 A 8/1008 6. The method of claim 5 p characterized _f in that the second step (crystallization) is used at a high temperature in a vessel equipped with a graphite inner layer vessel _B as claimed in claim 3 when the first operation is performed, which is closed in the ultra-vacuum as close as possible the starting material, after a slight excess of tellurium, optionally containing a dopant, has been introduced. 7. The method according to claim 5, characterized in that the second Operation (crystallization) at high temperature, namely one near the melting point of the stoechiometric mixture of cadmium telluride is carried out in a closed quartz vessel with a graphite inner layer, the Partial pressure of one of the components by adjusting the temperature of a part of the vessel where a crucible is located contains at least one of the substances, the partial pressure of which is to be kept constant, is set. 8. The method according to claim 7 »characterized in that the substance placed in the crucible is a pure substance and the temperature T _{2 of} the crucible is kept lower than the temperature T ^ of the melt during crystallization. 9ο method according to claim 8 "characterized in that in the Crucible except for one of the two components cadmium or tellurium volatile dopant is given " 10 .. A method according to claim 7 "characterized ,, that the concentration of one of the constituents is controlled of the gas above the molten bath by measuring the atomic absorption of Lieh" tes ₉ by measuring for controlling a Regelvor- "to 9 409848/1008 Direction known type is used, which _{acts on the temperature T 2} in the sense that the concentration of the substance in question in the gas is kept at the specified ¥ ert. 11. The method according to claim 7, characterized in that the substance added to the crucible in a little volatile amphoteric LÖ-. Simgsmittel is dissolved, the temperature T _{2 of} the crucible during crystallization equal to the dei? Melt is held. 12. The method of claim I1, characterized in that said given in the crucible material is selected "us the group of binä _~: ren alloys of cadmium tin, indium * gallium, zinc, the binary alloys of tellurium with tin, indium, Gallium and zinc,. and the cadmium halides. 13. The method according to any one of claims 5 to 12, characterized that the third step (crystallization) by SeIa- * tiwerschrift the vessel against the temperature gradient of the furnace is carried out, the vessel by means of known devices is rotated and made to vibrate. 14. The method according to any one of claims 1 to 13, characterized in that after the second operation (crystallization at high temperature) the crystal is dissolved and the third operation (recrystallization to single crystal) is carried out at low temperature in the vicinity of the melting point of the pure tellurium is by placing the ingot obtained in the second operation, after purification along with a very large excess of tellurium in a vessel, wherein the concentrations are selected such that the alloy is at 900 ⁰ C melts. 409848/1008 Τ5 · The method according to claim 14 »characterized in that» the Add dopant to the batch of a vessel with a graphite inner layer and close the vessel as close as possible to the contents under ultra-vacuum. 16. The method according to claim 14 »characterized in that the third operation (umcrystallization) for the production of single crystals at low temperature in a closed (sealed) quartz vessel with a graphite inner layer is carried out and the partial« pressure of one component is carried out by regulating the temperature T _{2 of} a Part of the vessel is set where a crucible is located which contains at least the dopant »whose partial pressure is to be kept constant. 17. The method according to claim 16, characterized in "that the concentration of the gas in dopant above the molten bath is regulated by measuring the atomic absorption of the light by allowing the result of the measurements to act in a manner known per se to control the temperature T ₂ " that the temperature T ₂ controlled in this way keeps the concentrations of the dopant in the gas at the specified value. 18. The method according to claim 16, characterized in that the dopant is dissolved in the crucible in a low volatile ampho.tären solvent and the Temperafar T _{2 of} the crucible during crystallization is kept equal to the temperature of the molten bath. 19. The method according to any one of claims 14 to 18 “characterized in that the third operation (Umkristallisation) in one Tellurium solvent by moving the vessel relative to the temperature 409848/100 8 temperature gradient of the furnace while rotating and vibrating, the vessel means known devices is carried out. 20. The method according to one of claims 1 to 13 _9, characterized _t that (after the second operation, high-temperature crystallization} of the formed crystal dissolved, and a single crystal is generated at a low temperature near the melting point of pure tellurium by doped a zone of shifts liquid tellurium through the exit crystal and thereby so moves that when the Lösiichkeitsgrenze of the dopant is not exceeded in Tellurlösungsmittel, an output crystal is chosen was doped _ff of the course of the second working passage (high-temperature crystallization) of the same Dotierungsraittel to the concentration of dopant to keep constant in the solvent zone as it progresses, and " if the solubility limit of the dopant in the solvent zone is exceeded, the concentration of dopant remains constant without a crystal having to be used, which at the high temperature primary crystallization was doped, and a non-doped crystal is selected. 21. The method according to claim 2O _9, characterized in that the single crystal growth in a quartz vessel with a graphite inner coating under ultra-vacuum at a temperature that is changed in the vessel with high temperature gradients in the order of 180 ° c / cm between 500 and 900 ⁰ C, is carried out. 22 ο Method according to one of Claims 1 to 21, characterized in that that at least one of the three operations is carried out under an inert gas atmosphere. 409848/1008 23. Device for performing the method according to one of the claims 1 to 22, characterized by a) Devices for cleaning the cadmium and tellurium by the zone melting process; b) Devices for filtering the cadmium and tellurium under water toffatmosphäre; c) Vessels in which the mixture of cadmium and tellurium of synthesis and is subjected to a first crystallization; d) a tilting furnace to carry out the synthesis in a horizontal position and for cooling in a vertical position; e) ovens for carrying out crystallizations at high temperature and low temperature; f) vessels »which contain crucibles into which the constituents are placed» whose vapor partial pressure is to be kept constant; g) Devices for measuring atomic light absorption in the gas phase above the melt h) devices for controlling the temperature T ₂ according to the concentration of the constituent under consideration measured in the gas phase; i) Provisions for carrying out the production of single crystals Displacement of a solvent zone containing; 11) an oven with a heating ring, which is the vessel in which the crystallization takes place, heated only over a small part of its height; 12) mechanical devices that keep the vessel perpendicular and in keep rotating around a vertical axis. 24. The device according to claim 23 _8, characterized in that the furnace-vessel arrangement is inclined and the vessel is kept in constant rotation _{9 to} maintain the contact liquid-ingot and the gas space on a single side between the liquid s of the vessel wall and the To bring ingots » 409848/1008 Blank page