Measurement of the direct energy gap of coherently strained Sn_xGe_(1–x)/Ge(001) heterostructures

The direct energy gap has been measured for coherently strained Sn_xGe_(1–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 Sn_xGe_(1–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.