Light-Hole States in Highly Tensile-Strained Ge Quantum Well

Si-compatible low-dimensional systems have been exploiting either tensile strained Si or compressively strained Germanium (Ge) quantum wells (QWs). For quantum information, the latter has been explored in new schemes for hole spin qubits. Hole spins have attracted a great deal of attention. Nevertheless, most of experimental investigations on 2D gas systems have so far focused on heavy-hole states (HH) due to the compressively strained heterostructure currently exploited, where the valence band degeneracy is lifted and leaves HH states energetically above the light-hole (LH) states. However, the ability to exploit LH states will be a powerful paradigm beneficial for quantum information technologies. To harness these largely unexplored advantages of LH states, we present a new low-dimensional system consisting of highly tensile strained Ge quantum well grown on Si wafers using GeSn as barriers. Several spectroscopic techniques were used to identify the LH confined states in the Ge well. The obtained heterostructure shows optical transitions that are modulated in the midinfrared range. This ability to engineer quantum structure where LH is the ground state in an optically active group IV platform lays the groundwork for a new class of Si-compatible quantum technologies.