The crystal perfection depends on the superheating of the mother phase too — experimental facts and speculations on the “melt structure” of semiconductor compounds

Abstract

Depending on the degree of superheating, the “structure” of the melt, especially of associated liquid semiconductors with a high ionic contribution to the bond energy (II–VI, IV–VI), may affect the nucleation process and growth kinetics, and, hence, the crystal quality very strongly. Superheating-supercooling experiments in Bridgman ampoules show a distinct increase in the degree of supercooling in stoichiometric CdTe and PbTe melts being superheated in excess of a critical value above the melting point. In contrast, small transient and drastically increased supercooling has been obtained in non-stoichiometric melts containing an excess of tellurium. Moreover, the holding time in the molten state may influence the supercooling, as has been found in PbTe. Obviously, the destruction of associated melt complexes requires a certain degree and time of superheating or dissolution by the excess component. Hence, an inadequate superheating of stoichiometric melts before the crystal growth process may preserve strongly associated growing-in units that affect the growth kinetics (nucleation mode, substructure, twinning) and growth orientation considerably.