Continuous-Wave Magneto-Optical Determination of the Carrier Lifetime in Coherent Ge 1 − x Sn x /Ge Heterostructures

We present a magneto-optical study of the carrier dynamics in compressively strained ${\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ films with $\mathrm{Sn}$ content up to 10% epitaxially grown on $\mathrm{Ge}$ on $\mathrm{Si}$(001) virtual substrates. We leverage the Hanle effect under steady-state excitation to study the spin-dependent optical transitions in the presence of an external magnetic field. This allows us to obtain direct access to the dynamics of the optically induced carrier population. Our approach reveals that at cryogenic temperatures the effective lifetime of the photogenerated carriers in coherent ${\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$ is on the subnanosecond timescale. Supported by a model estimate of the radiative lifetime, our measurements indicate that carrier recombination is dominated by nonradiative processes. Our results thus provide central information to improve the fundamental understanding of carrier kinetics in this advanced direct-band-gap group-IV-material system. Such knowledge can be a stepping stone in the quest for the implementation of ${\mathrm{Ge}}_{1\ensuremath{-}x}{\mathrm{Sn}}_{x}$-based functional devices.