Power-dependent Transient Gain Study on Direct Gap GeSn Crystallized on Amorphous Layers

摘要

In this study we investigate the power-dependent femtosecond transient gain of direct-gap Ge_(0.91)Sn_(0.09) thin films crystallized on amorphous SiO_2 layers. At carrier injection density Δn<1 × 10~(17) cm~(-3), there is no optical bleaching. When An increases to ～8×10~(18) cm~(-3), the Ge_(0.91)Sn_(0.09) film becomes transparent at λ～2000 nm. At higher injection of Δn～2 × 10~(19) cm~(-3), net transient gain is observed at λ=1900-2150 nm, with a peak gain of 6300 cm~(-1) at λ=2000 nm. Further increasing Δn to ～1×10~(20) cm~(-3), the peak of transient gain red-shifted to 2100 nm due to the bandgap renormalization, and the peak gain further increases to ～8000 cm~(-1). The transient gain coefficient of Ge_(0.91)Sn_(0.09) is similar to III-V direct bandgap semiconductors at similar injection levels. The gain lifetime was measured to be ～0.1 ns at λ=2100 nm and Δn～6×10~(18) cm~(-3). These results confirm that direct-gap GeSn crystalized on amorphous SiO_2 is a good optical gain medium towards 3D photonic integration.