Direct-gap Ge/GeSn/Si and GeSn/Ge/Si heterostructures

Abstract A theoretical proposal is given for creating direct-gap semiconductor layers in silicon-based Group IV heterostructures. Based upon recent bandstructure calculations for pseudomorphic Ge/GeSi and GeSi/Ge, we predict a strain-induced Γc-Lc direct-gap crossover (λg ∼ 2.2 μm) in tensile Ge/Ge0.87Sn0.13 and in compressive Ge0.98Sn0.02/Ge. We used linear extrapolation of band-edge curves. The direct-gap structures are potentially useful in laser diodes, electrooptic modulators, and photodetectors.