Hole spin relaxation and intervalley electron scattering in germanium

Hole spin relaxation and intervalley electron scattering in bulk Ge at 300 K are distinguished and selectively investigated using a spectrally, temporally, and polarization-resolved pump-probe differential transmission technique that takes advantage of the indirect band gap nature of Ge and of the differing circular selection rules for the direct split-off and heavy-hole valence-to-conduction band transitions. Spin-polarized carriers are injected across the direct gap by a circularly polarized pump. Subsequently, the circular dichroisms associated with direct across-gap interband transitions from the split-off and heavy-hole valence bands are measured by a probe pulse tuned to interrogate both transitions. We demonstrate that the Pauli-blocking of the conduction states needed for the direct transition from the split-off valence band by electrons dominate the dichroism in the differential transmission for early times, but once the electrons scatter to the side valleys, the dichroism reverses sign and is caused by the holes blocking the initial valence states needed for the direct heave-hole transition, thus, allowing us to study the hole dynamics. From these measurements, we estimate an intervalley scattering time of similar to 200 fs and an effective hole spin relaxation time of similar to 700 fs.