A Platform for Light-Hole Qubits in Group IV Semiconductors

Si-compatible quantum devices have been exploiting either tensile strained Si or compressively strained Ge QWs, which are the only group IV systems that can currently be routinely obtained using SiGe as growth template and barrier layers. For quantum information, the former has been used as the building block for electron spin qubits, whereas the latter has been explored in new schemes for hole spin qubits. Herein, we present a third low-dimension system consisting of highly tensile strained Ge QW integrated on an optically active platform and discuss its basic properties experimentally and theoretically. The growth of tensile strained Ge QW is achieved using direct bandgap GeSn as barrier layers grown on silicon wafers. This heterostructure yields high tensile strain in Ge QW and band structure corresponding to a sizable LH-HH splitting exceeding 100 meV. Unlike compressively strained Ge, the top of the valence band is occupied by LH in tensile strained Ge. We also found a high LH g-factor anisotropy in Ge/GeSn QW, with g = 21.8 for in-plane B-field and g = 0.69 for perpendicular-to-plane field. These properties lay the groundwork to implement LH spin qubits with potentially easier manipulation due to the combined effects of the large Rashba-type SOI, and the spin ½ of LH.