Enhanced direct bandgap emission in germanium by micromechanical strain engineering.

We propose a new class of optoelectronic devices in which the optical properties of the active material is enhanced by strain generated from micromechanical structures. As a concrete example, we modeled the emission efficiency of strained germanium supported by a cantilever-like platform. Our simulations indicate that net optical gain is obtainable even in indirect germanium under a substrate biaxial tensile strain of about 1.75% with an electron-hole injection concentration of 9 x 10(18) cm(-3) while direct bandgap germanium becomes available at a strain of 2%. A large wavelength tuning span of 300 nm in the mid-IR range also opens up the possibility of a tunable on-chip germanium biomedical light source.