Optical orientation of electron spins and valence-band spectroscopy in germanium

We have investigated optical orientation in the vicinity of the direct gap of bulk germanium. The electron spin polarization is studied via polarization-resolved photoluminescence excitation spectroscopy unfolding the interplay between doping and ultrafast electron transfer from the center of the Brillouin zone towards its edge. As a result, the direct-gap photoluminescence circular polarization can vary from 30% to -60% when the excitation laser energy increases. This study provides also simultaneous access to the resonant electronic Raman scattering due to inter-valence-band excitations of spin-polarized holes, yielding a fast spectroscopic approach for the determination of the energy spectrum of holes in semiconducting materials.