MOLECULAR-DYNAMICS SIMULATIONS OF VIBRATIONAL LIFETIMES IN AMORPHOUS-SILICON

Recent theoretical and time resolved Raman studies disagree on the lif etime of high energy vibrational modes in amorphous silicon. The latte r suggests that the lifetime increases with increasing frequency and i s of the order of 10 ns for the highest frequency modes, while the for mer predicts a picosecond timescale that follows the two-phonon densit y of states. Here we present the results of molecular dynamics simulat ions which are complementary to the perturbative calculations. At diff erent temperatures, kinetic energy is put into selected modes of vibra tion in 216 and 4096 atom systems with periodic boundary conditions an d the Stillinger-Weber potential. The lifetime of medium and high freq uency modes is found to be of the order of 10 ps at 5, 10 and 30 K, in qualitative agreement with the perturbative calculations.