title: Tunable optical gap at a fixed lattice constant in group-IV semiconductor alloys.
abstract: A direct absorption edge tunable between 0.8 and approximately 1.4 eV is demonstrated in strain-free ternary Ge_{1-x-y}Si_{x}Sn_{y} alloys epitaxially grown on Ge-buffered Si. This decoupling of electronic structure and lattice parameter-unprecedented in group-IV alloys-opens up new possibilities in silicon photonics, particularly in the field of photovoltaics. The compositional dependence of the direct band gap in Ge_{1-x-y}Si_{x}Sn_{y} exhibits a nonmonotonic behavior that is explained in terms of coexisting small and giant bowing parameters in the two-dimensional compositional space.
authors.affiliation: Department of Physics, Arizona State University, Tempe, Arizona 85287-1504, USA. vdcosta@asu.edu
authors.forename: V R
authors.initials: VR
authors.lastname: D'Costa
authors.forename: Y-Y
authors.initials: YY
authors.lastname: Fang
authors.forename: J
authors.initials: J
authors.lastname: Tolle
authors.forename: J
authors.initials: J
authors.lastname: Kouvetakis
authors.forename: J
authors.initials: J
authors.lastname: Menéndez