Vibrational modes of oxygen in GaP including nearest-neighbor interactions

A theoretical treatment of the vibrational modes of substitutional defects in zinc-blende crystals is presented. The dynamics of the perfect lattice are described with the use of a two-parameter model including nearest-neighbor interactions only. The defect consists of an impurity atom with variable strength nearest-neighbor force constants. For the case of oxygen in GaP, the theoretical defect vibrational modes are compared with experiment. Agreement between theory and experiment is obtained for values of the defect force constants which are 15% of the bulk values for the O° and ${\mathrm{O}}^{+}$ defects, indicating that the oxygen impurity is quite weakly bonded in the lattice.