Feasibilty of laser action in strained Ge and Group IV alloys on Si platform

Group IV elements and their alloys show poor light emission due to their indirect gap. Application of tensile strain in Ge lowers the ?? valley below the L valleys in bulk as well as in Ge nanowires. We present also our results on direct gap type I alignment showing direct gap at ~ 0.8 eV in Si_1-p-qGe_p C_q (C <4%) active layers with Ge_1-x-ySi_xSn_y as the barrier. We have chosen a composition to give the critical thickness as high as possible and estimated its absorption coefficients: both fundamental and free carrier, by using theoretical expressions, available data for Ge and suitable interpolation. The linear gain spectra, and transparency carrier density for the chosen heterostructure are then estimated. The threshold current density for an optimized structure may be approximately 300 A/cm².