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Cultivation by a method of directional crystallisation

Cultivation of monocrystals of germanium by a method of directional crystallisation was spent on the original procedure developed on chair of applied physics of the Tver university [51,163,164]. The essence of an expedient consists in directional crystallisation of a melt of germanium in graphite tigle on monocrystal zatravochnyj a crystal.

A form-building device which gives demanded a lateral view to a crystal, the crucible - its restricting surfaces (a bottom and a lateral part) is. The construction of a thermal knot executed from graphite and including a folding crucible, system teploizolirujushchih screens (ground, lateral, upper), a heater, allows kristallizovat all volume of a melt in tigle without occurrence of voltages in a crystal and without fracture tiglja.

Zatravochnye crystals were made of monocrystals of germanium with crystallographic orientation and a dislocation density no more 4∙103cm ' 2. A long axis Angle of deflection zatravochnogo a crystal from 54

The given crystallographic direction made no more than 4 °. Cultivation atmosphere - vacuum, an equipment material - graphite. The graphite crucible is a form-building device; its diameter (lateral view) corresponds to diameter (size) of a grown up crystal in the form of a disk (the lateral view shape), and depth spots a thickness of a crystal.

In drawing 2.2 samples of crystals of the germanium, explored are presented

In the present operation.

Drawing 2.2 - the Large-sized crystals which have been grown up by a method of directional crystallisation and, and a method Chohralsky in

The basic technological features for decrease in flaws are decrease in lapse rates of temperatures in a crystal and a melt, regulation of the shape of front of crystallisation, decrease in concentration of background impurities, first of all oxygen.

Vytjagivanie monocrystals Ge it is yielded in the environment of inertial gas, vacuum or hydrogen at the pressure equal atmospheric or 10'Па. At cultivation of crystals of major diameter in vacuo additional problems can arise because germanium possesses the high latent heat of melting at rather low thermal conduction [165 169].

Principal cause of the defective structure is presence of the thermal voltages arising in a crystal under the influence of axial and radial lapse rates of temperature. Energy of thermal voltages leads to crystallographic detrusion and will be conversed to energy of dislocations.

Thus, for cultivation of monocrystals of germanium with low density of flaws, first of all, it is necessary to shape the homogeneous temperature field with the underload temperature lapse rates as in a melt, and a crystal.

It is necessary to consider also, that germanium has a cubic crystalline lattice of type of diamond. Plastic detrusion in a lattice of the given type occurs most possibly on slip planes (111). Thus the detrusion direction parallelly an axis [110], i.e. a dislocation lays in a plane (111) while the detrusion vector (vector Bjurgersa) is parallel an axis [110]. In this connection cultivation bezdislokatsionnyh germanium monocrystals is most often drawn with an exit of a facet (111) on a demarcation a crystal - a melt. Thus the shape of front of crystallisation has great value.

It is observationally proved, that bezdislokatsionnye monocrystals inconvertiblly grow in that case when there are requirements for formation at the front crystallisation of a smooth plane (111).

Cultivation of crystals on a method Chohralsky is accompanied by the continuous tap of warmth from its surface, leading to occurrence of the temperature lapse rates which quantity depends on intensity of its cooling. In this connection the central place in technology of reception of qualitative ingots of germanium is occupied with a regulation problem warmly - and a mass transfer and temperature lapse rates in a melt and a crystal [136]. C the practical point of view the solution of the given problem is reduced to working out of a construction of a thermal knot and its devices promoting decrease of thermal streams from a surface of a crystal for the purpose of reduction of axial and radial lapse rates of temperature.

As technical features of methods different constructions of heaters, tiglej, equipments, cultivation atmosphere, flux presence on melt surfaces, the self-acting control of growth, action of a magnetic field and other features can be used.

Spotting role in the course of occurrence of flaws in monocrystals process warmly-massoperenosa in system plays a melt - a crystal-surrounding medium. For an estimate of possibility of reception of perfect monocrystals it is necessary to analyze rostovuju system for the purpose of an establishment of its influence on thermal fields in a melt and a crystal and, accordingly, on formation of structure of a crystal.

On the basis of theoretical examinations it is possible to formulate following features of processes of cultivation of monocrystals with low concentration nano - and the microdimensional flaws:

Axial and radial temperature lapse rates in a melt and a crystal should be low; rough quantities of values of lapse rates of temperatures in a crystal close crystallisation front should not exceed 1-2 To/sm for axial and 0,5-1,0 To/sm for radial lapse rates of temperatures;

Temperature allocation on crystal height should be odyonorodnym and have a linear relation - an axial lapse rate of temperature should be to stationary values;

The crystallisation front should be flat or slabovognutym, that can be provided with aspiration to zero of a radial lapse rate of temperature should aspire to zero (isotherms near to crystallisation front in a melt and a crystal should have the flat shape; the cone height razrashchivanija an ingot should be not less than its diameter.

2.1.2

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A source: Ivanova Alexandra Ivanovna. Micromorphology of a surface and dislocation structure of large-sized optical crystals of germanium and paratellurita. The dissertation on competition of a scientific degree of the candidate of physical and mathematical sciences. Tver - 2015. 2015

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