Magneto-Optical Characterization of GeSn Quantum Wells

Gate-defined quantum dots (GDQDs) in germanium heterostructures have emerged as promising platforms for hosting spin qubits in quantum information processing. A promising material system is provided by germanium-tin (GeSn) thin films. Most notably, GeSn offers a direct band gap for tin concentrations above ~6% that enables optical access to the material, as well as a large spin-orbit coupling that may boost the speed of coherent control of quantum dot spin qubits. In this work, we leverage the direct band gap properties of GeSn in the mid-infrared regime to perform magneto-optical characterization of bulk and a double quantum well GeSn samples. We perform the characterization by implementing a Fourier Transform Infra-Red based photoluminescence (PL) spectroscopy while modulating an above band gap excitation and utilizing lock-in amplification. First, temperature-dependent PL spectroscopy exhibits an expected red shift of photon energy as the temperature increases. Second, power-dependent PL measurements indicate that laser-induced heating is negligible. Third, magnetic field-dependent measurements at a temperature of 20 K show a diamagnetic shift at lower fields and a Zeeman splitting at higher fields. Finally, an observation of shift in the PL at a magnetic field of 12 T indicates an effective g-factor of a GeSn double quantum well of |g*| ~ 2.00. Our study sheds light on the potential of GeSn heterostructures as a promising platform for the spin qubits in semiconductor GDQDs.