Vibrational modes of oxygen in GaP including second-nearest-neighbor interactions

The localized and resonant vibrational modes of a substitutional oxygen defect in GaP have been computed with the use of the Green's-function approach. A 15-parameter version of the deformable-dipole model was used to describe the lattice dynamics of bulk GaP. A defect, consisting of a mass perturbation at the substitutional site and a perturbation among the nearest- and second-nearest-neighbor short-range interactions near the oxygen atom, was considered. The local modes, labeled by symmetry, are presented as a function of the interaction perturbation. Quantitative agreement with experimental results for O0 and O+ defects is obtained by weakening the O (-Ga and -P) short-range interactions to 38% of the bulk values while weakening the Ga-P back bonds. With the inclusion of Coulomb effects, this corresponds to an effective O-lattice force constant of 3.5 eV/2, which is 25% of the bulk, P-lattice value. © 1984 The American Physical Society.