Effects of high carrier densities on phonon and carrier lifetimes in Si by time-resolved anti-Stokes Raman scattering

The relaxation times T-1 of nonequilibrium populations of elementary excitations in Si are studied by time-resolved Raman scattering using a subpicosecond pump-probe method. Incoherent anti-Stokes Raman scattering is used to monitor the decay of the nonequilibrium populations of holes and the generation and decay of zone-center longitudinal optical (LO) phonons. At lower levels of laser excitation, hole and LO phonon T-1 lifetimes are less than 0.2 ps and greater than 1.6 ps, respectively. At higher laser intensities, the lifetime of holes increases and the lifetime of LO phonons decrease toward a common value of T-1 similar to 0.4 ps. (c) 2007 American Institute of Physics.