Disorder Defects Modelling for Some Ternary Crystals
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Disorder Defects Modelling for Some Ternary Crystals Valeriy G.Voevodin, Olga.V.Voevodina Siberian Physico-Technical Institute 1 Revolution sq., 634050, Tomsk, Russia ABSRTACT The attempt to obtain the data on thermodynamic parameters and equilibrium concentrations of disorder defects was made. Quasi-chemical model of the defects formation with allowance for Schottky and Frenkel defects was used. Thermodynamic parameters were calculated based on Weiser’s technique. Six types of the disorder defects in II-IV-V2 and I-III-VI2 were considered. Used models, approaches and initial parameters give that the greatest concentration (~ 1019 cm-3) and accordingly the greatest influence on properties of the crystals have defects AB or BA. INTRIDUCTION There is no complete consent in an estimation of influence of antisite defects on properties of II-IV-V2-crystals. At the same time there are the reasons to suppose that just these defects play the important role in an optical absorption in the transparency region of these crystals perspective for use in mid-IR nonlinear optics. The task of the work was an attempt to obtain data on thermodynamic parameters and on dependence of equilibrium concentrations of disorder defects upon liquidus temperature near to the point of ternary compound of Gibbs triangle as a stage of work on study of a behaviour of intrinsic point structural defects in the semiconductors and on definition of their homogeneity region. CALCULATION MODEL The calculation of equilibrium concentration of defects was based on a model of defects formation taking into account processes of formation of Schottky, Frenkel and disorder defects and also processes of interaction of the crystals with a gas phase in an approximation of nonvolatility of the elements A1, B4. ( notifications [1] are used; M, N are constituents of ABC2 compound). ×
×
0 ↔ VA× 2 + VB×4 + 2VC×5
A 2A 2 ↔ A 2 (g) + VA× 2
× M ×M ↔ VM + M i×
B4B4 ↔ B4 (g) + V
M i× + VN× ↔ M ×N
2C5C5 ↔ 1 / 2 C54 (g) + VC×5
×
×
×
4
B
×
(1)
×
Application of the action mass law to the processes (1) allows to obtain an appropriate set of equations for equilibrium constants of quasi-chemical reactions (1). There is a great number of methods for definition of the thermodynamic parameters the defects and it is necessary to notice that the results, obtained with use of different models and methods, differ rather hardly even for elementary and binary semiconductors. The more so it is possible for multinary semiconductor AA4.20.1
compounds. Probably, it is necessary to use greater number of models, techniques and approaches, in order to find the calculation conditions that correspond to reality in the best way. Models and techniques of work [2] were used for the calculation of the Frenkel defects concentration, that is only two sorts of interstitials (cation and anion tetrahedral) were considered, the third sort of interstitials (hexagonal) did not take into account in the given work. An enthalpy of vacancies formation was estimated according the technique offered by
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