Optical Orientation of Spins in Ge/SiGe Multiple Quantum Wells grown (111) Si Substrate

We present the first experimental study of spin-dependent phenomena in Ge-based heterostructures grown on high index surfaces. Here we focus on the optical investigation of Ge/SiGe Multiple Quantum Wells (MQWs) deposited on (111)-oriented Si substrate. These heterohepitaxial systems spontaneously possess the removal of the L valley degeneracy, recently suggested as key ingredient for achieving exceptionally long spin lifetimes in Ge. In particular, we carried-out measurements of the decay time of photoluminescence (PL) revealing electron lifetime in the tens of nanosecond regime at cryogenic temperatures. On the other hand, polarization-resolved PL measurements was used to achieve robust optical orientation of spins, as known in these heterostructures. Our result yields an important step forward the comprehension of physical mechanisms governing the spin relaxation of electrons in (111)-oriented Ge/SiGe MQWs heterostructures, and opens the way towards the realization of a new generation of Ge-based emitters able to combine standard microelectronic properties with tailored spin-dependent effects.