Local force variations due to substitution impurities in nine compounds with the zinc-blende structure

Abstract

A Green's-function technique and a rigid-ion model including general forces between nearest neighbors, next-nearest neighbors, and Coulomb forces were used to calculate the frequency of vibrational modes against the relative variation of forces between nearest neighbors $\frac{\Delta f}{f}$ for some isolated atomic substitutions in nine compounds possessing the zinc-blende structure: GaP, GaAs, GaSb, InSb, InAs, ZnSe, ZnTe, ZnS, CdTe. By comparison of these results with existing experimental data it was possible to determine $\frac{\Delta f}{f}$ for each particular case. For isoelectronic substitutions this quantity can be far from zero and reaches -53% in the case of B on Ga in GaP, still higher values being obtained for nonisoelectronic substitutions (for example, -87% for beryllium substituted on gallium in GaP). These values are found to depend largely on the force model adopted for the perfect crystal and especially on the way in which the forces between next-nearest neighbors are taken into account. No general correlation was observed between the size of the impurity compared with the atom it replaces and the $\frac{\Delta f}{f}$ values, which however are clearly related to the donor or acceptor situation of this impurity: for GaAs, where a term of comparison exists, our results agree quite well with those given by a recent model accounting for local charge and polarizability changes consistent with this situation.