Electric field control of photoluminescence polarization in Ge/SiGe quantum wells

Spin manipulation is a crucial aspect for fundamental investigations and the future application of spin-based optoelectronics [1]. Within this field, group IV semiconductors have shown appealing properties such as long spin lifetime, isotopic purification and compatibility with Si manufacturing processing. For practical purposes, electrically-induced spin manipulation through the Rashba effect would be highly desirable [2]. However, such a possibility has received little attention in heterostructures made of group-IV materials. In this work we present a polarization-resolved photoluminescence study in a cylindrical p-i-n diode where the intrinsic region of the device consists of Ge QWs in Si_0.15Ge_0.85 barriers. Different excitation power densities are investigated in a bias range from -5 to +4V. At 4K we observed a non-monotonic behaviour of the degree of circular polarization when varying the optical pump density and a non-trivial response with the bias, suggesting the presence of competing dynamical effects. Our work presents a starting point for a deeper understanding of spin-dependent properties in group IV heterostructures and their fine control by electrical means.
[1] De Cesari et al, Electronics, 6, 19 (2017)
[2] A. Manchon et al., Nat. Mater. 14, 871 (2005)