PARTICULAR SINGULAR FACES IN SINGLE CRYSTALS. A. I. Kolesnikov and Yu. M. Smirnov, Tver State University, 170000 Tver, Russia

In the course of the investigation of the growth, morphology and structural defects in germanium single crystals we have defined the main morphological features of dislocation-free germanium crystals [1].

The single crystals were grown in the <111> crystallographic direction by the Czochralski method. The crystal-melt interfaces of the crystals grown were flat mirror singular {111} faces (F-planes according to the Hartman's conception of PBS vectors). In addition, also observed were narrow stripes of {110} faces on the lateral sides of the crystals (S-planes according to the above conception).

On the basis of the study of dislocation-free germanium and silicon single crystals we arrived at a principle of a particular singular face. These faces are singular, but are characterized by the least possible specific surface free energy. For germanium and silicon these are faces with the crystallographic symbol {111} . The free energy of the germanium {111} face is 0.85-1.10 J.m^-2, while the free energy of the {110} face is 1.30-1.35. J m^-2 . For other faces the free energy is considerably higher.

The principle was realized in the development of the growth process of paratellurite (tellurium dioxide) single crystals. As was deduced theoretically, in paratellurite single crystals the face of minimum specific free energy is face {110} , the energy of faces {101} , {111} , {201} and others being considerably higher. We were able to obtain paratellurite single crystals as the growth pyramids of particular {110} face. The single crystals were 80 mm in diameter and 80 mm in height. The samples obtained were free of three-dimensional structural defects (bubbles), while the dislocation density was below 3 [10³ cm^-2 [2].

[1] Yu. M. Smirnov. The growth of dislocation-free germanium single crystals. Non-ferrous Metals (USSR), 1977, No.5, p.48 (in Russian).

[2] Yu. M. Smirnov and A. I. Kolesnikov. The conception of particular singular face (after the example of paratellurite). In: Physics of Crystallization (Tver, TSU, 1994), p. 24 (in Russian).