Measurement of the direct energy gap of coherently strained SnxGe1−x/Ge(001) heterostructures

The direct energy gap has been measured for coherently strained SnxGe1−x alloys on Ge(001) substrates with 0.035<x<0.115 and film thickness 50–200 nm. The energy gap determined from infrared transmittance data for coherently strained SnxGe1−x alloys indicates a large alloy contribution and a small strain contribution to the decrease in direct energy gap with increasing Sn composition. These results are consistent with a deformation potential model for changes in the valence and conduction band density of states with coherency strain for this alloy system.