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flaws of crystalline structure (a general characteristic and the basic classification)

Increase of requirements to cleanliness and structural homogeneity of the monocrystals applied in optics, akustooptike, Ik-optics, optoelectronics and a photonics, is related to aspiration to the peak pinch of functionality and performances of corresponding semiconductor electronic devices.

All natural and synthesised monocrystals and in even bolshej degrees crystal grains of polycrystals differ from ideal themes that various infringements of structure of a crystal contain.

In a number of operations communication between structural flaws in germanium and optical inhomogeneities in these crystals is in detail studied. In particular, correlation between intensity of dispersion of light and a dislocation density in germanium is found out. The spatial distribution of dislocations and specific electroresistance on crystals [6-12] are explored malouglovye boundaries, and also.

The interrelation between a kinetics of growth of crystals of germanium and formation of flaws of structure of various dimensionalities, including dislocations [13-17] is much less full explored. It is caused as essential difficulties of the observational character at measurings of the instantaneous growth rates and temperature oscillations at the front crystallisations, and on lack of well developed theory, allowing to count the kinetic coefficients.

On the standard classification to structural flaws of crystalline materials carry infringements of ideal transmitting symmetry of a crystalline lattice [18-20]. Flaws make essential impact on many properties of solid bodies: an electrical conductivity,
Photoconduction, thermal conduction, velocity of diffusion, magnetic properties, hardness, strength and plasticity, density etc. Dependence of these parametres of a solid body on flaws can appear is so great, that as a result they will be spotted not so much by initial structure of a material, how many type and number of flaws in it. Parametres, not sensitive to structural flaws, strictly speaking, are not present, but practically such parametres as fusion temperature, an inductivity, paramagnetic and diamagnetic performances, elastic modules, it is possible to carry to the parametres feeblly depending on influence of flaws. It is obvious, that, the more purely and more absolutely the material, the this influence is more appreciable. Many semiconductor linkings are phases of a variable composition with more or less wide field of existence. Properties of such linkings are spotted mainly by the nature and concentration of dot flaws. Guidance strukturnoyochuvstvitelnymi is reduced by properties of materials to a select of methods and an establishment of the requirements providing possibility of controllable introduction of flaws of certain type in a lattice of a crystal or in the course of its cultivation, or at its aftertreatments [18-21].

There are some expedients of classification of flaws [19-26]: division of flaws on natural and the impurity, and also viewing of flaws from balance positions in system (equilibrium and nonequilibrium). The impurity flaws are caused by presence of stranger atoms or molecules. Natural flaws do not change a qualitative composition of a crystal (only quantitative composition varies). Their occurrence is related to influence of temperature, mechanical radiative and other views of action on a firm phase. Concentration of equilibrium flaws for a concrete crystal unequivocally depends on temperature.

It is necessary to consider the kinetic factor as travel of atoms to solid bodies even at heats is carried out slowly enough. Therefore exact conformity should consider time of achievement of an equilibrium state.

Nonequilibrium flaws also are subject to temperature influence. At keeping a crystal with flaws at a stationary value raised) temperature long-term enough time, can occur so-called temperature otzhig flaws in which process concentration of nonequilibrium flaws decreases. It occurs at the expense of increase of their mobility. However, at crystal returning to initial (under) temperature concentration of such flaws is not recovered, that is there is a direct communication of concentration of flaws with temperature which takes place in case of equilibrium flaws.

The most detailed is classification of flaws by geometrical signs - dot and protjazhennye. Dot (nulmernye) flaws are characterised by that lattice contortions are concentrated in neighbourhoods of one knot, that is localised on distances of the order interatomic and; at protjazhennyh flaws their sizes in one, two and three directions accordingly essentially exceed value and. protjazhennye flaws can be linear (dislocations), plane (interphasic boundaries) and volume (pores, flaws).

Nulmernye (dot) flaws

To nulmernym to flaws carry flaws which are related to bias or replacement of small group of atoms (natural dot flaws), and also with impurities. They arise at a heating, a doping, in the course of crystal growth and as a result radiative irradiation. Properties of such flaws and mechanisms of their formation are most studied, including a motion, interaction, an annihilation, transpiration [19-21, 25-26].

Vacancies, as well as other dot flaws, are centres of strain (dilatation): the particles surrounding a vacant knot. Vacancies are biased concerning balance standings (in knots of a crystalline lattice), that leads to occurrence of an internal field of mechanical voltages. On major distances g from vacancy the field of voltages decreases as l∕r5. In volume of a perfect crystal single vacancies to appear and
Cannot disappear; as radiants (and sinks) vacancies the surface of a crystal, boundary of grains serve in a polycrystal, to a dislocation. Processes of formation and destruction of vacancies together with mezhuzelnym atom (Frenkel's steams) are possible also. Energy of vacancy depends on voltages in a crystal.

Natural mezhuzelnyj atom - the atom of a basic element which is in an interstitial standing of an unit cell. Atoms or the ions surrounding mezhuzelnyj atom, are biased from the standings of balance in knots of a lattice and can change a charging state. These biases and redistribution of electrons are spotted from a requirement of a minimum of a free energy of a crystal with mezhuzelnym atom. If biases are small in comparison with the interatomic distance, the implanted atom occupies one of interstices in a lattice and is mezhuzelnym in literal sense. The impurity substitutional atoms exchange atoms of one type another in a knot of a crystalline lattice, and the impurity settles down in an interstice of a crystalline lattice.

Dot flaws and their association in crystals play the important role in the theory of a solid body and an explanation of the electrical phenomena in semiconductors, conductivity of solid bodies, phase changes, optical properties, a chemical bond in crystals.

The one-dimensional (linear) flaws

The one-dimensional flaws represent flaws of the crystal which size in one direction is much more than lattice parametres, and on two another - is commensurable with it. To the linear flaws carry dislocations and disclinations.

Boundaries of field of not complete detrusion in a crystal - dislocations are characterised by a detrusion vector (vector Bjurgersa) and a corner φ between it and a dislocation line. At φ - 0 dislocation is, at φ =90o - regional, at other corners - immixed and then can be spread out to screw and regional builders. Dislocations arise in the course of crystal growth; at its plastic strain and in many other things cases. A disclination -
Boundary of field of not complete rotational displacement in a crystal. It is characterised by a rotational displacement vector. Dislocations make major impact both on processes of growth of crystals, and on their mechanical properties. In semiconductors they influence, besides, and on electrical properties. Dislocations participate in processes of formation and disappearance of natural dot flaws (atoms in interstices, vacancies), giving the chance to these processes to transit in a crystal and excepting necessity of diffusion to an exterior surface of a crystal.

Two-dimensional flaws

Or surface defects flaws of packing, malouglovye boundaries (representing associations of dislocations), boundaries of doubles and grains, a surface of a crystal are two-dimensional. The surface defects breaking in a crystal, are restricted by the full either partial dislocations or disclinations.

Three-dimensional flaws

The aggregations of vacancies forming pores and channels concern three-dimensional (volume) flaws; the particles subsiding on various flaws vials (decorating), for example, of gases, vials matochnogo a solution; aggregations of impurities and growth bands. As a rule, it is pores or inserts of the impurity phases. An origin - infringement of modes of growth of a crystal, decay of a supersaturated firm solution, pollution of samples.

The basic difference of dot flaws from the linear, two-dimensional and volume flaws consists that they can exist in a crystal both in termodinamicheski equilibrium, and in metastable states at terminating temperature [19-26].

The linear, two-dimensional and volume flaws are the metastable formations arising at growth, mechanical strain or at thermal processing of a crystal. Flaws influence practically all properties of a crystal. Each type of flaws in own way influences on strukturnoyochuvstvitelnye properties of a material: the diffusion phenomena (a motion

Dot flaws), plasticity (a motion of dislocations of flaws), fracture (origin and growth of flaws at dislocations), rekristallizatsija, dvojnikovanie, phase

And dot

Integrating

Transmutations (a motion mezhzerennyh and interphasic boundaries), the radiative phenomena (changes of properties of crystals under the influence of the prompt particles creating dot flaws), the electrical, optical and other properties caused by interaction of charge carriers with flaws. At presence in a crystal of major number of various flaws it is impossible to gain a material with controllable parametres. In this connection before materials technology and technology there is a problem of reception of structurally perfect and pure materials or materials with certain type and concentration of flaws, that is such materials which parametres could be drived. Therefore finding-out of the parents of occurrence of various structural flaws, studying of their behaviour in a crystal, their influences on those or other parametres of a material, working out of management methods by concentration of flaws are the major problems of materials technology and technology [20-27]

Cultivation of monocrystals of germanium and paratellurita from a melt is usually accompanied by occurrence in them of thermoelastic voltages and structural flaws. The view of flaws, their allocation in volume of a monocrystal and concentration depend on reception requirements - a method of cultivation, temperature requirements, the sizes of monocrystals and other factors.

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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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