Confinement and Threshold Modeling for High Temperature GeSn and GeC/GeCSn Lasers

Models of GeSn and GeCSn quantum well (QW) lasers were compared to predict net gain and threshold for computing applications. GeSn showed weak confinement of electrons in both k-space (directness) and real space, as well as a weak optical confinement factor. Using material parameters from ab-initio calculations, adding 1-2% carbon to Ge or GeSn could provide all three confinements simultaneously, with up to 350 meV of electron confinement by Ge QW barriers and a direct bandgap that is 50-220 meV below the indirect gap. A 2-4x increase in electron effective mass preserves strong confinement even in narrow, 5 nm GeCSn/Ge quantum wells. Simply keeping electrons out of non-lasing, higher energy states doubles the differential gain compared with GeSn lasers and reduces free carrier absorption, while deeper QWs further enhance gain. GeCSn laser thresholds as low as 160 A/cm ² are predicted for operation at temperatures of 100 °C, two orders of magnitude lower than comparable GeSn lasers.