Optical gain in short period Si/Ge superlattices on [001]-SiGe substrates

Results are here presented for the electronic band structure and the material gain of selected Si/Ge superlattices grown on Ge and SiGe buffers along the [001] direction. The chosen superlattices were proposed in the literature as promising direct-gap candidates based on group IV materials. A sp3d5s* tight-binding model has been adopted for the evaluation of the bands and the material gain in the presence of realistic charge injection levels and for different polarizations of the radiation associated with the direct transitions. For the superlattices studied here, we show that in the most favorable case (Si2/Ge14) the peak gain values are only a factor of 6 weaker than the corresponding value obtained for a typical III-V direct gap bulk crystal.