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

The ability of tailoring the value of 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 novel spintronic devices. Quantum confinement has been shown to be an effective means to tailor the electron g factor in heterostructures based on III-V compounds. Nevertheless, to date no experimental demonstration has been provided in Ge which is a CMOS compatible material, although such an effect was predicted in Ge/SiGe quantum wells (QWs) by Baron et al. in 2003. In this work we measured for the first time Electron Spin Resonance (ESR) signal of conduction electrons in Ge/SiGe QWs deposited on Si substrates, observing four ESR lines in the region of g values between 0.8 – 1.93. We show that the g factor of confined electrons is highly anisotropic and reflects the C3v symmetry of the L valleys of the conduction band, similarly to bulk Ge. Our data prove that confinement leads to a larger g factor in the QWs with respect to the bulk, in full agreement with the theoretical predictions. Preliminary studies of the lineshape highlighted that the linewidth is anisotropic and that it is broadened due to the roughness of the interface between the QW and barrier layers. Data suggest that both the transverse and the longitudinal spin relaxation times are anisotropic, and that the latter is affected by confinement effects. In conclusion, our findings open new pathways for manipulating spin properties in Ge nanostructures and for developing spintronic functionalities on the mainstream well-established silicon platform.