Theoretical Modeling for the Interaction of Tin Alloying With N-Type Doping and Tensile Strain for GeSn Lasers

We investigate the interaction of tin alloying with tensile strain and n-type doping for improving the performance of a Ge-based laser for on-chip optical interconnects. Using a modified tight-binding formalism that incorporates the effect of tin alloying on conduction band changes, we calculate how threshold current density and slope efficiency are affected by tin alloying in the presence of tensile strain and n-type doping. Our results show that while there exists a negative interaction between tin alloying and n-type doping, tensile strain can be effectively combined with tin alloying to dramatically improve the Ge gain medium in terms of both reducing the threshold and increasing the expected slope efficiency. Through quantitative modeling, we find that the best design is to include large amounts of both tin alloying and tensile strain but only moderate amounts of n-type doping, if researchers seek to achieve the best possible performance in a Ge-based laser.