Theoretical study of the optical gain characteristics of a Ge_1-xSn_x alloy for a short-wave infrared laser

Optical gain characteristics of Ge_1-xSn_x are simulated systematically. With an injection carrier concentration of 5×10¹⁸/cm³ at room temperature, the maximal optical gain of Ge_0.922Sn_0.078 alloy (with n-type doping concentration being 5×10¹⁸/cm³) reaches 500 cm^-1. Moreover, considering the free-carrier absorption effect, we find that there is an optimal injection carrier density to achieve a maximal net optical gain. A double heterostructure Ge_0.554Si_0.289Sn_0.157/Ge_0.922Sn_0.078/Ge_0.554Si_0.289Sn_0.157 short-wave infrared laser diode is designed to achieve a high injection efficiency and low threshold current density. The simulation values of the device threshold current density J_th are 6.47 kA/cm² (temperature: 200 K, and λ =2050 nm), 10.75 kA/cm² (temperature: 200 K, and λ =2000 nm), and 23.12 kA/cm² (temperature: 300 K, and λ =2100 nm), respectively. The results indicate the possibility to obtain a Si-based short-wave infrared Ge_1-xSn_x laser.