Ultrafast thermalization of nonequilibrium holes inp-type germanium studied by femtosecond infrared spectroscopy

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Abstract
Relaxation of holes photoexcited to the splitoff valence band by femtosecond pulses in the mid-infrared is directly monitored via the transient inter-valence-band absorption. Two thermalization processes are distinguished. The excited carriers undergo inter-valence-band scattering within 100 fs and thermalize with time constants around 700 fs. In contrast, equilibration of unexcited holes occurs within 100 fs. Theoretical calculations show that the dynamically screened Coulomb interaction among the holes and emission of optical phonons represent the main scattering mechanisms.