Electron Spin Resonance of conduction electrons in Ge/SiGe quantum wells

The ability of tailoring the Landé g-factor in semiconductors is appealing because it is related to the possibility of tuning the spin-orbit interaction in the solid state and ultimately to control the spin-dependent properties via external fields in spintronic devices. Quantum confinement has been shown to be an effective mean to tailor the electron g-factor in III-V heterostructures. Nevertheless, to date no experimental proof was shown in Ge which is a CMOS compatible material, although such an effect was predicted in Ge quantum wells (QWs) by Baron et al., Phys. Rev. B 68,195306 (2003). Here we report the first Electron Spin Resonance (ESR) measurements of conduction electrons in Ge/SiGe QWs on Si. ESR lines in the 0.8 to 1.93 g-factor range are observed, showing that the g-factor of confined electrons in the L valley is highly anisotropic, similarly to the bulk. Our data prove that confinement increases the g-factor in QWs with respect to bulk Ge, in full agreement with the theoretical predictions. The lineshape study highlighted that the spin relaxation is governed by Elliot-Yafet type processes, typical for centrosymmetric materials. Longitudinal spin relaxation times were measured from the power dependence of the lines, providing exceptionally long values with respect to bulk Ge. These findings open new pathways for manipulating spin properties in Ge-based nanostructures, encouraging the development of spintronic functionalities on the mainstream Si platform