Femtosecond interband hole scattering in Ge studied by pump-probe reflectivity

Abstract

We have measured the transient reflectivity changes of bulk Ge after excitation with 140 fs laser pulses at 1.5 eV. The electron and hole dynamics are calculated using an ensemble Monte Carlo method. We find that the observed reflectivity changes are due to three main mechanisms: diffusion, band gap renormalization, and carrier dynamics, particularly scattering of light holes to the heavy hole band via the optical deformation potential interaction. Because of the unique band structure of Ge and the use of a reflectivity technique, we can isolate the role of the light holes with femtosecond time resolution. The Monte Carlo simulation (which uses an optical deformation potential for holes of d 0=46 eV) overestimates the scattering rate of light holes to the heavy hole band. The agreement can be improved when a lower value for the deformation potential (determined from theory or other experiments) is used.