Light-Hole Spin Confined in Germanium

The selective confinement of light holes (LHs) in tensile strained germanium (Ge) is achieved by introducing Ge₁₋ₓSnₓ/Ge/Ge₁₋ₓSnₓ heterostructures. By evaluating their electronic structure as a function of Sn content, residual strain, and Ge well thickness., it is shown that above 12\,at.% Sn and below $0.4%$ residual compressive strain in the barriers, the tensile strain in Ge becomes sufficiently large to yield a valence band edge with LH-like character, thus forming a quasi two-dimensional LH gas in Ge. The LH ground state has a larger in-plane effective mass than that of heavy hole (HH) in Si1-yGey/Ge/Si1-yGey quantum wells. LHs in optimal Ge₁₋ₓSnₓ/Ge/Ge₁₋ₓSnₓ heterostructures exhibit a strong g-tensor anisotropy, with the in-plane component one order of magnitude larger than that of HHs in planar systems. Moreover, two of three structure-inversion-asymmetry Rashba parameters, both of which are critical in electric-dipole-spin-resonance (EDSR) experiments, are effectively ten times the size of the cubic Rashba parameter in HH quantum wells. In the regime of LH selective confinement, every layer of the heterostructure is of direct bandgap which can be relevant to achieve efficient optical photon-spin qubit interfaces. This work discusses the broad landscape of the characteristics of LH spins confined in Ge to guide the design and implementation of LH spin-based devices in Ge.