Momentum(k)-space carrier separation using SiGeSn alloys for photodetector applications

A band-structure engineering approach is proposed to use semiconductor alloys such as SixGe1-x-ySny with a direct bandgap slightly above the indirect fundamental bandgap to demonstrate momentum(k)-space carrier separation of photogenerated carriers in photodetectors to reduce dark current. This approach combines the large absorption coefficient of direct-gap semiconductors with the long carrier lifetime of indirect gap semiconductors and reduces tunneling current due to the large effective masses of the indirect valleys. When the difference of the direct and indirect bandgaps (i.e., the energy difference between the direct and indirect valleys) varies from 0.4 to 3kBT, the direct-bandgap absorption covers a wide wavelength range from 2 to 22 μm for those alloys lattice matched to GeSn virtual substrates and to various commercially available substrates. The same approach can be adopted for other material systems.