Direct band-gap hexagonal Silicon-Germanium type-I quantum wells

Abstract

Hexagonal SiGe alloys offer a group IV direct bandgap for integrated photonics, addressing the limitations of traditional silicon-based electronics. We have synthesized coaxial nanowire shells comprising direct bandgap hex-Ge/SiGe and hex-SiGe/SiGe Quantum Wells (QWs) around a wurtzite GaAs core. Time-resolved photoluminescence measurements demonstrate a 1 nanosecond radiative lifetime, proving direct bandgap emission. Photoluminescence spectra show the QW emission in between the emission of the well and the barrier material, indicating type-I band alignment. Measurements as a function of QW thickness demonstrate clear quantum confinement with emission up to room temperature for thick QWs. By changing the QW-thickness and the well composition, the emission could be tuned between 2000-3400 nm. The experimentally observed direct bandgap SiGe QWs with type-I band alignment are expected to be pivotal for the development of novel low-dimensional devices based on hex-Ge and hex SiGe.