Direct bandgap germanium-on-silicon inferred from 5.7% <100> uni...

We report uniaxial tensile strains up to 5.7% along <100> in suspended germanium (Ge) wires on a silicon substrate, measured using Raman spectroscopy. This strain is sufficient to make Ge a direct bandgap semiconductor. Theoretical calculations show that a significant fraction of electrons remain in the indirect conduction valley despite the direct bandgap due to the much larger density of states; however, recombination can nevertheless be dominated by radiative direct bandgap transitions if def