Local-mode frequencies due to substitutional impurities in zinc-blende-type crystals. II. Effect of force-constant changes

Abstract

A model which has earlier been seen to be successful in explaining the main features of the infrared absorption due to Be impurities in CdTe has been employed to understand the local-mode frequencies in different III-V and II-VI semiconducting compounds. The effects of force-constant changes due to various impurities in a large class of the compound semiconductors have been studied. The local-mode frequencies have been calculated and discussed with the existing experimental and theoretical data. It has been observed that in the case of isoelectronic impurities the force-constant changes are well within \ifmmode\pm\else\textpm\fi{} 20%, whereas in the case of other impurities, e.g., Li isotopes in III-V and II-VI compounds and Al impurities in II-VI compounds, the force-constant changes are as large as \ifmmode\pm\else\textpm\fi{} 58%. The force-constant changes are similar for the different isotopes of an impurity atom. The differences in the ionic radii of the impurity and the host ions are not suggestive of the probable force-constant changes in these compound semiconductors.