GAAS HOMOGENEITY REGION AND POINT-DEFECT CONCENTRATION CALCULATION IN TERNARY-SYSTEMS GA-AS-ELECTRICALLY ACTIVE IMPURITY

Thermodynamic calculations of homogeneity region of Sn-, Te- and Si-doped GaAs were carried out to analyse equilibrium and supersaturated native point defect behaviour during crystallization and postcrystallization cooling. Arsenic Frenkel, Schottky and antisite defects are included in the model with the Frenkel defects being dominating. Besides decomposition Ga- (or As-) supersaturated nonstoichiometric solid solution which takes place in the two-phase region of the phase diagram at temperatures below 800-1000°C, a great amount ( ≈ 1019cm-3) of arsenic vacancies and interstitials become overquilibric on postcrystallization cooling immediately after crystallization, which leads further to the high-temperature aggregation process. The great difference in point defect formation energies causes their transformation to each other and leads to significant decrease of increase of arsenic antisite concentration on cooling of Ga- or As-rich crystals respectively. Narrowing of low-temperature (850-1000°C) boundaries of GaAs homogeneity region on Sn and Si doping accomplished by a shift of congruent point to Ga-rich compositions stimulate Ga-supersaturated nonstoichiometric solid solution decomposion. The so-called superdilation phenomena may be due to the great amount of gallium interstitials formed at the very initial stage of the decomposition. Te-doping shifts GaAs homogeneity region to the As-rich compositions and makes lateral surfaces of existence region to twist around the axis of elongation of the latter. © 1990.