We have measured the transient reflectivity changes of bulk Ge after e
xcitation with 140 fs laser pulses at 1.5 eV. The electron and hole dy
namics are calculated using an ensemble Monte Carlo method. We find th
at the observed reflectivity changes are due to three main mechanisms:
diffusion, band gap renormalization, and carrier dynamics, particular
ly scattering of light holes to the heavy hole band via the optical de
formation 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 hea
vy hole band. The agreement can be improved when a lower value for the
deformation potential (determined from theory or other experiments) i
s used. (C) 1997 Elsevier Science Ltd.