Evidence of strong spin–orbit interaction in strained epitaxial germanium

Spin–orbit interaction effects are of great interest, primarily for the ability to modulate spin transport in a semiconductor channel for device applications. In particular, the Rashba spin–orbit (S–O) interaction allows for a tuneable spin modulation response dependent on the applied electric field, which can be achieved using standard semiconductor gate technology. We present evidence of the Rashba S–O interaction in two modulation doped germanium (Ge) quantum well (QW) heterostructures with different layer structures, and consequently different band structures and internal electric fields across the QW region. We show that two complementary low temperature magnetotransport analyses can be used to identify and quantify the Rashba S–O parameter in these materials, although quantification is limited in one case due to significant parallel conduction. We highlight that both techniques (Weak Antilocalisation and Shubnikov de-Haas oscillations) should be used when analysing a new material system as other conduction and magnetoresistive effects can obscure evidence of the Rashba S–O interaction in one or both of these regimes