The problem of doping of non-stoichiometric phases

An overview and analysis of our experimental data on the crystal structure, mechanical, thermal, galvanomagnetic and electrical properties of the non-stoichiometric semiconducting IV–VI phases under doping are presented. The peculiarities and general regularities of the doping of these phases by introduction of elementary impurities and by cation substitution are considered. The presence of non-stoichiometric vacancies in the cation sublattice of the host compound leads to the appearance of a new, in comparison with a crystal free of defects, mechanism of impurity dissolution consisting in occupation of vacancies by impurity atoms. This process is accompanied by a decrease in microhardness and charge carrier concentration, and an increase in charge carrier mobility and lattice thermal conductivity. It is shown that there is correlation between the value of impurity solubility limit and relative difference in ionic radii of IV atoms and those of the impurity. Under cation substitution, the existence of a large number of non-stoichiometric defects in the host compound determines the specificity of the concentration dependences of the properties in the range of small impurity concentrations. The introduction of cations with variable valence leads to a specific effect caused by the presence of non-stoichiometric vacancies and consisting in the recharging of cations under changing impurity atom concentration or deviation from stoichiometry.