Optical injection of spin current in Ge_1-xSn_x

Ge_1-xSn_x is a silicon-compatible semiconductor of great interest because of the possibility to engineer the bandgap energy and directness, and the potential for designing monolithic photonic and optoelectronic devices. In this work, we exploit the recent developments made in establishing high-quality, direct bandgap Ge_1-xSn_x layers, to investigate the optical injection and coherent control of spin currents in this group IV semiconductor. The study of these processes could play a key role in the development of coherent photon-to-spin interfaces, thus providing the foundation to create compact optical schemes for long distance distribution of entanglement. To this end, a full zone 30-band k·p model is applied to obtain the band structure of relaxed and strained Ge_1-xSn_x. For one- and two-photon absorption, the optical injection of carrier, spin, current, and spin current are calculated in the independent particle approximation. Critical properties such as the two-photon absorption anisotropy and linear-circular dichroism are also extracted. Finally, coherent control with a bichromatic field of frequencies ω and 2ω is investigated. In this case, with the incorporation of Sn in Ge, a significant increase in spin current injection is found for a relatively broad range of energies.