Method of crystal growing

FIELD: crystal growth.

SUBSTANCE: method comprises crystal growing in two stages: growing alloyed crystals used for making blanks of seeds made of a disk of a given diameter and approximately 5-6-mm thick and subsequent growing of nominally pure crystals.

EFFECT: enhanced quality of crystals.

3 dwg

 

The invention relates to a method of growing single crystals of compounds with high vapor pressure over the melt in the growth conditions at normal atmospheric pressure by the Czochralski method. The inevitable consequence of this fact is caused by thermal evaporation (not concentration) subcooling the surface of the melt below the melting point. Hypothermia, significant at the interfacial boundary crystal-melt leads to a significant deviation of the shape of the solidification front from the flat, which is known to be the most preferred in the practice of growing crystals.

In the literature there are ways and methods of reducing the magnitude of hypothermia in podcastalley region due to changes in the hydrodynamics of the melt: the increased speed of the grown crystal leads to a change in the dominant free convection forced. Because most of the crystals increase in speed leads to a twisting deformation and destruction, such a control of the shape of the solidification front may be unacceptable.

A device for growing crystals containing the crucible with the melt, means for controlling the speed of rotation of the crystal, insert in the form of a body of rotation about the axis of the crucible, the diameter of which is larger than the diameter of erasepage crystal, rigidly connected with the crucible is lowered into the melt so that its edges are located above the edge of the crucible, means for automatically maintaining a constant melt level and above insert, inside the above-mentioned external insert additional fixed rigidly bonded with her inner coaxial insert, which is located below the level of the melt (EN 2191853, WITH 30 IN 15/24, With 30 15/12, publ. 2002.10.27).

A disadvantage of this device is the need to maintain a constant melt level, carried out additional automatic water make-up as the fall of the level of the melt, which leads to complication of the installation.

There is a method of growing crystals of yttrium-aluminum garnet(Y3Al5O12)doped to generate radiation activating ions of rare earth elements, in order to reduce the convexity of the crystallization front are ions of dysprosium, Dy [Facetting and Optical Perfection in Czochralski grown Garnets and Ruby, B.Cockayne et al., J. of Materials Science, 4 (1969), pp.450-456]. With the availability of a wide range of homogeneity between grenades composition Y3Al5O12and Dy3Al5About12the authors were able to obtain almost flat crystallization front by increasing the concentration of Dy. For these crystals the control of the shape of the front through radiant heat is the exchange of the melt is quite relevant from the point of view of their purpose - generation of laser radiation.

However, for most crystals used, for example, in the acousto-optics and scintillation technology, doped crystals are markedly inferior to its nominally pure counterparts at odds of acousto-optic q-switched or their light yield, since the creation of acousto-optic devices with high diffraction efficiency or scintillation calorimeters with great performance requires the use of materials with high optical transparency at the operating wavelength. For example, crystals bO4and PbWO4this method leads to deterioration of acousto-optical and scintillation properties of the grown crystals.

The aim of the invention is to provide a method for growing crystals of compounds with high vapor pressure over the melt at normal atmospheric pressure by the Czochralski method, in which instead of the traditional increase in the number of revolutions of the crystal control of the shape of the crystallization front is through radiant heat transfer to the melt. The above technical result ensures that the method of growing crystals of compounds with high vapor pressure over the melt at normal atmospheric pressure by the Czochralski method, comprising the first stage of the growing crystal from the melt, legerov the frame ions, absorbing the radiation of the melt, on the second stage of the doped crystal is made billet seed in the form of a disk of a given diameter with a thickness of about 5-6 mm, which then grow nominally pure crystal from the melt.

The significance of differences of the present invention is defined by the fact that this new seed harvesting allows you to grow nominally pure crystal with a planar solidification front due to the absorption of radiation melt its alloy part. The latter fact is important for the optical homogeneity of the grown crystals, because when using them in special purpose devices (acousto-optic devices, fast scintillators for synchrotron radiation and other) optical transparency at the operating wavelength is maximum.

The proposed method consists of 2 stages, which includes the cultivation of doped crystals, which are used for the procurement of seeds of a given diameter for subsequent cultivation of nominally pure crystals.

1 stage. From the melt containing the estimated amount of the impurity absorption in the crystal radiation melt grown series doped crystals of the desired diameter. Further, to completely remove the internal voltage is th crystals are annealed in bigradient zone resistance furnace, after which they are calibrated on the grinding machine to the specified diameter. Then calibrated crystals are subjected to Stripping (shaded areas) with their subsequent cutting for manufacturing a template bare blanks special configuration, the number of which is determined by the length of the cylindrical part of the grown crystal. Seed harvesting have the form of discs, one side of which goes to the rounded pin inserted in structurally fixed, in turn, into the collet Chuck on the mechanism of stretching. The thickness of the disk part of the bare workpiece (about 5-6 mm) is selected from the following considerations: at the stage of “seeding” and selecting the best mode of the growing crystal (mode thermodynamic equilibrium of the seed crystal with the melt) possible deviations from equilibrium, i.e. the melt (case of excessive overheating of the melt), or, on the contrary, the occurrence (in the case of hypothermia) around the seed crust solidified melt. In the described conditions, the thickness of the disk part of the bare workpiece should be sufficient for the successful procedure of selecting the optimal mode of cultivation.

II stage. In the crucible with nominally pure melt immersed seed harvesting, which in accordance with the above-described process is uroy grown crystal, already not containing impurities. After cultivation and subsequent annealing of the crystal is cut to separate it from billet seed, which can be used successfully in subsequent multiple processes of cultivation. The new seed harvesting, containing a certain part of the nominally pure crystal, significantly reduces, rather eliminates the possibility of doping the crystal with impurity in comparison with the initial seeding alloy seed. The latter fact is important for the optical homogeneity of the grown crystals, because when using them in special purpose devices (acousto-optic devices, fast scintillators for synchrotron radiation and other) optical transparency at the operating wavelength is maximum.

The invention is illustrated figure 1-3. Figure 1 (a-d) shows the sequence of operations: (a) calibration of the crystal grown from the melt mixed with (dotted line); b), C) - layout and Stripping a cylindrical workpiece (shaded areas); d) cutting the parts and b) making the bare workpiece; d) growing nominally pure crystal on the seed harvesting. Figure 2 presents the temperature distribution in the melt of the molybdate of lead and shape of the crystallization of cu is Stella in conditions of supercooling of the melt. Figure 3 presents images of crystals grown at different concentrations of rare earth impurities in the melt.

The method can be explained as follows.

It is known that crystals of most high-temperature oxides, melts which do not have hypothermia, caused by evaporation, grown by the Czochralski method, mainly from the superheated relative to the melting point of the melt, or at least at the temperature of its surface, close to the melting point. Therefore, at the moment of “seeding”, when the source terminal (the seed) kristallicheskogo material is brought into contact with the melt to select the optimal mode of cultivation, often clearly drawn drip liquid column (meniscus) of the melt, the boundary of which coincides with the isotherm temperature of melting (crystallization). If overheating occurs separation of the seed from the melt. In the sign, by the way, is the determination of the optimal mode of cultivation, i.e. the determination of the conditions of thermodynamic equilibrium coexistence seed crystal with the melt. The above conditions of overheating of the melt does not occur, however, when growing crystals, melts which have volatility (molybdates and wolframates calcium and lead - Samoa4, CWO 4, PbMoO4, PbWO4, sapphire, - Al2O5; paratellurite - teo2and others). The above-mentioned drip-liquid post, if occurs, it most likely indicates that the melt excessively overheated, and the seed very quickly will be “cut off” (podpravlena) in the melt. The most typical pattern for melts of these compounds is almost complete absence of meniscus due to supercooling of the melt, which is grown crystal “seeks” to reduce sprouting into the melt in the form of a cone-shaped protrusion. In fact, the latent heat of crystallization, which in the absence of evaporation is usually given through the growing crystal out (up), in the case being considered is spent on compensation of hypothermia in the field under the crystal. According to the degree of advancement in the melt solidification front can judge the magnitude of hypothermia, since the crystal growth below the level of the melt will cease at the moment when the top of the conical protrusion isotherm reaches the melting temperature grown connection.

Figure 2 presents the temperature distribution in the melt of lead molybdate is a typical representative compounds with high vapor pressure over the melt and the position of the isotherms growth (solidification front)due to thermal subcooling RA is floating due to its evaporation.

From the analysis of the given data characterizing the behavior of melts with volatility and, consequently, evaporation, it follows that the evaporation of the melt due to the high elasticity of vapor and vapor of its constituent oxides, accompanied by significant hypothermia, which, in turn, leads to micromorphologically instability of interfacial boundary is strongly jutting into the melt shape of the crystallization front. This form may result in crystals of stress, often resulting in plastic deformation.

In the practice of crystal growth control of the shape of the crystallization front by changing the speed of rotation of the crystal (i.e. changes dimensionless parameter, the Reynolds number) is a traditional and commonly used technique. However, for most materials, including molybdate of lead, taken as an example, the revs can cause serious morphological distortion of the crystals and, ultimately, to complete their destruction.

In this regard, the development of a method of controlling the shape of the crystallization front through radiant heat transfer in growing such crystals becomes of practical importance.

When growing optical crystals > 80% of the heat away from the boundary Krista is l-melt radiation through the growing crystal. When the melt surface hypothermia, caused by evaporation, radiation heat loss of the melt through the growing crystal are even more hypothermia, which leads to further “ingrowth” conical protrusion in the melt by lowering the level at which the isotherm is the melting point of the grown material. Thus, the task is to create conditions for absorption by the crystal radiation from the melt to reduce the degree of supercooling. According to the Stefan-Boltzmann law the integral emissivity εtabsolutely black body is proportional to the 4th degree of its absolute temperature:

εt=σT4,

where σ=5.67×10-18W/m2K4- Stefan - Boltzmann constant. According to the Wien displacement law, you can find the wavelength at which the emissivity of a heated body max: λmax=A/T where V=2.898×10-3MK - permanent Fault. Therefore, to melt bO4having without overcooling TPL=1065°C λmax=2.1 μm. It follows that the bandwidth bO4(λ=0.42-5.5 μm) crystal is virtually transparent to the greater part of thermal radiation of the melt, i.e. it works as a fiber wire, through which radiation is Nergy away from the interface.

As shown by the results of our experiments, the admixture of many rare-earth ions created in the crystal bO4absorption bands in sufficient proximity to λ=2.2 μm, and a significant part of the radiation is absorbed within the crystal. Figure 3 presents images of crystals grown at different concentrations of rare earth impurities in the melt. It is seen that with increasing concentration of impurities of the crystallization front shape changes from conical to almost flat. Thus, from the analysis of solidification conditions bO4defining morphological features of its growth, it follows that among the parameters affecting the shape of the phase boundary crystal-melt, the significant role of impurities, as a management tool radiant heat transfer. It would seem that the management of radiant heat transfer in terms of alloying of the melt and, consequently, the crystal sufficiently solves the problem of getting a flat crystallization front, provides even penetration of the impurity along the length and the cross section of the crystal. Crystals PbMoO4doped with ions of rare-earth elements, can actually be used as matrices for solid-state laser with a low threshold excitation, but also as a potential material for lasers with tunable frequency. From this point of view is described in the above method for controlling the shape of the crystallization front is really reasonable and even necessary. It should be noted, however, that, considering the main purpose of this crystal as one of the most important (after teo2) acousto-optic materials doped crystals are markedly inferior to its nominally pure counterparts at odds of acousto-optic figure of merit (M2), because, as noted above, the creation of acousto-optic devices with high diffraction efficiency requires the use of a material with high optical transparency at the operating wavelength” from Here it becomes clear that to obtain nominally pure highly perfect crystals with flat crystallization front shape, you must use ways to control radiant heat melt proposed in this application.

The method of growing crystals of compounds with high vapor pressure over the melt at normal atmospheric pressure by the Czochralski method, comprising at the first stage, the crystal is grown from a melt doped with ions, absorbing the radiation of the melt, characterized in that the second additional stage of the doped crystal is made billet seed in the form of a disk of a given diameter with a thickness of about 5-6 mm, which then grow nominally pure crystal from the melt.



 

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FIELD: crystal growth.

SUBSTANCE: method comprises crystal growing in two stages: growing alloyed crystals used for making blanks of seeds made of a disk of a given diameter and approximately 5-6-mm thick and subsequent growing of nominally pure crystals.

EFFECT: enhanced quality of crystals.

3 dwg

FIELD: production of solar batteries, integrated circuits and other semiconducting devices.

SUBSTANCE: the invention presents a method of production of alloyed monocrystals or polycrystals of silicon and may be used in production of solar batteries, integrated circuits and other semiconductor devices. The substance of the invention: the method of SUBSTANCE: the invention presents a method of production of alloyed monocrystals or polycrystals of silicon includes preparation of the initial charge consisting of 50 % of silicon alloyed with phosphorus with a specific electrical resistance of 0.8-3.0 Ohm·cm or boron with specific electrical resistance of 1-7 Ohm·cm, its melting-down and consequent growing of crystals from the melt, in which additionally enter elements of IV group from the periodic table by Mendeleyev, in the capacity of which use germanium, titanium, zirconium or hafnium use in concentrations of 1017-7·1019 cm-3. The invention allows to produce chips with high values of life time of minority carrier (LTMC), high homogeneity of electric resistivity (ER) and high concentration of oxygen, with a low concentration of defects and increased thermostability and radiation resistance.

EFFECT: the invention ensures production of chips with high values of LTMC, high homogeneity of ER and high concentration of oxygen, with a low concentration of defects and increased thermostability and radiation resistance.

2 cl, 4 ex, 1 tbl

FIELD: crystal growing technologies.

SUBSTANCE: invention relates to technology of growing crystals for passive laser shutters used in modern lasers operated in IR spectrum region. Crystals are grown according to Chokhralsky method from initial stock melt containing metal oxide mixture, namely produced via solid-phase synthesis gallium-scandium-gadolinium garnet of congruently melting composition with magnesium and chromium oxide additives assuring concentration of chromium and magnesium cations in melt 2.0·1020 to 2.6·1020 at/cm3. Process is carried out at cell pressure 1.4 atm in argon and carbon dioxide medium with carbon dioxide content 14-17% by volume. Invention makes it possible to grow perfect crystals of gallium-scandium-gadolinium garnets alloyed with chromium cations, which are characterized by absorption coefficient above 5 cm-1 within wavelength 1.057-1.067 μm generation range.

EFFECT: achieved required Q-switching mode in continuous and pulsed operation conditions.

6 ex

FIELD: chemistry; passive Q-switch crystal growing process.

SUBSTANCE: production process for growing crystals of galium scandium gadolinium garnets is based on Czochralski process, which implies crystal growing from initial molten batch, which is congruently melting gallium scandium gadolinium garnet produced by 3-phase synthesis, doped with magnesium oxide and chromium oxide. These oxides provide for 2.0×1020-2.6×1020 atoms/cm3 concentration of cromium and magensium cations in melt during the first crystal growing, in argon with 14-17% of carbon dioxide, pressure in chamber being 1.3-2.0 atm. For the second, third and subsequent growths, an initial batch amount equal to previous crystal weight, cromium and magnesium content in batch being determined according to formula (СCr×СMg)/1020 = 0.5÷2, where СCr is at least 5×1019 atoms/cm3, is added to the crucible.

EFFECT: provides for required Q-switched mode, continuous or pulse, within wavelength range of 1,057-1,067 mcm.

2 ex

FIELD: technological process.

SUBSTANCE: invention is related to growing of garnets single crystals and may be used in laser equipment, magnet microelectronics (semi-conductors, ferroelectrics) and for jewelry purposes. Single crystals of terbium-gallium garnet are prepared by Chochralski method by means of melting primary stock, which includes clarifying calcium-containing additive, and further growing of single crystal from melt to primer. As primary stock mixture of terbium and gallium oxides is used, as calcium containing additive - calcium oxide or carbonate, and after growing crystal is annealed in atmosphere of hydrogen at temperature of 850-950°C for around 5 hours until orange paint disappears.

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2 ex

FIELD: metallurgy.

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5 cl, 2 ex, 2 dwg

FIELD: metallurgy.

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1 ex

FIELD: physics, optics.

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10 cl, 9 dwg, 4 ex

FIELD: chemistry.

SUBSTANCE: invention relates to production of semiconductor materials and specifically to production of gallium antimonide monocrystals, which are used as substrate material in isoperiodic heterostructures based on ternary or quaternary solid solutions in Al-Ga-As-Sb and In-Ga-As-Sb systems, which enable to produce a wide range of optoelectronic devices (radiation sources and detectors in the 1.3-2.5 mcm spectral range). The method includes synthesis and growing a monocrystal using a Chochralski method in a hydrogen atmosphere on a seed crystal in the [100] crystallographic direction, wherein synthesis of the monocrystal is carried out in a single process with the flow rate of especially pure hydrogen in the range of 80-100 l/h and holding the melt at the synthesis step at 930-940°C for 35-40 minutes.

EFFECT: invention enables to obtain perfect large-size gallium antimonide monocrystals with diameter of 60-65 mm.

1 tbl

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