Feasibility of laser action at 1550 nm by direct gap type I GeC/GeSiSn heterojunctions

Application of tensile strain in Ge lowers the G valley below the L valleys but the direct gap is reduced from the value in unstrained Ge. We considered Ge_1-qC_q (C <4%) active layers with Ge_1-x-ySi_xSn_y as the barrier and estimated the range of compositions in the active and barrier layers to yield direct gap (~0.8 eV) type I alignment by using model solid theory. We have chosen a composition to give the critical thickness as high as possible and estimated its absorption coefficients by using theoretical expressions. 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.