Spin physics of Ge-based heterostructures

Spin physics of carriers in germanium (Ge) has been a hot topic of the last years, due to the expected very long spin lifetime in centrosymmetric semiconductors. The thesis reports about an all-optical investigation of the spin properties of carriers in Ge-based systems. The results of polarization resolved photoluminescence measurements on bulk Ge and Ge quantum wells (QWs) provided the experimental demonstration of optical spin injection and detection in these structures. The comparison of the measured polarization of the direct gap emission in bulk Ge samples with the results of a Monte Carlo simulation allowed us to outline the rich spin dynamics of the photoexcited electrons. On the other hand, in Ge QWs the study of the polarization of direct transitions between confined states demonstrates that strain and confinement can be used as tools to tailor the optical spin polarization. Information on the spin lifetime of conduction electrons are provided by the study of the indirect gap emission both in the bulk material and in the nanostructures. In particular, for intrinsic bulk Ge our results constitute the first experimental evidence of a predicted very long spin lifetime in the low temperature regime. The study of the spin lifetime of conduction electrons in Ge QWs is enriched by Electron Spin Resonance measurements, which in addition allowed us to address the g factor of confined electrons, demonstrating the effect of confinement on the spin-orbit coupling of conduction electrons.