Limitation of bulk GeSn alloy in the application of a high-performance laser due to the high threshold

Abstract

In this work, the gain characteristics of the GeSn alloy are systematically investigated with effective mass approximation theory, and the potential of bulk GeSn in the application of a high-performance laser is discussed. The gain could not be enhanced persistently as the mole fraction of Sn continuously increases and becomes negative as the Sn fraction beyond 18%. An Sn fraction dependent doping scheme is proposed to effectively reduce the threshold injected carrier density to the lowest of 1.10×1018 cm-3. The optimum doping type varies from n-type to p-type as the Sn fraction increases with the conversion fraction of 10%. With doping optimization, the lowest threshold current density of bulk GeSn based laser is predicted to be 1.225 kA/cm2 for a designed n-Si0.157Ge0.643Sn0.200/p-Ge0.84Sn0.16/p-Si0.157Ge0.643Sn0.200 double heterostructure laser, indicating the inadequacy of bulk GeSn alloy of being the gain material for a high-performance laser.