Phonon-defect scattering in doped silicon by molecular dynamics simulation

Molecular dynamics simulations are used to study the scattering of phonon wave packets of well-defined frequency and polarization from individual point defects and from a field of point defects in Si. The relative amounts of energy in the transmitted and reflected phonon fields are calculated and the parameters that influence the phonon scattering process are determined. The results show that the fractions of transmitted and reflected energies strongly depend on the frequency of the incident phonons and on the mass and concentration of the defects. These results are compared with the classic formula for the scattering strength for point defects derived by Klemens, which we find to be valid when each phonon-defect scattering event is independent. The Klemens formula fails when coupled multiple scattering dominates. The phonon density of states is used to characterize the effects of point defects on mode mixing.