A simple method was presented for the calculation of local vibrational modes in cubic semiconductors. This used the Keating-Kane valence-force model, together with Coulomb forces. The vibrational frequencies and amplitudes were deduced from the eigenvalues and eigenvectors of the dynamic matrix, respectively. The valence-force parameters of GaAs were obtained from calculations of the interatomic forces, using density functional theory. The resultant phonon dispersion curves were in agreement with neutron scattering data, and the local vibrational modes of Al symmetry at the As antisite were presented. The isotope shift of local vibrational modes was calculated for shallow impurities (B, C, N) in Si and for Ni impurities in ZnS. A general relationship between the mass dependence of a local vibrational mode and the relative vibration amplitude of the impurity was presented.

U.Scherz, C.Schrepel: Materials Science Forum, 1995, 196-201, 1583-8