DIRECT-GAP GE GESN/SI AND GESN/GE/SI HETEROSTRUCTURES/

A theoretical proposal is given for creating direct-gap semiconductor layers in silicon-based Group IV heterostructures. Based upon recent b andstructure calculations for pseudomorphic Ge/GeSi and GeSi/Ge, we pr edict a strain-induced GAMMA(c)-L(c) direct-gap crossover (lambda(g) a pproximately 2.2 mum) in tensile Ge/Ge0.87Sn0.13 and in compressive Ge 0.98Sn0.02/Ge. We used linear extrapolation of band-edge curves. The d irect-gap structures are potentially useful in laser diodes, electroop tic modulators, and photodetectors.