Enhanced direct bandgap emission in germanium by micromechanical strain engineering

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Abstract
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 1.5% with an electron-hole injection concentration of 9×1018 cm-3 while direct bandgap germanium becomes available at a strain of 2%. A large wavelength tuning span of 400 nm in the mid-IR range also opens up the possibility of a tunable on-chip germanium biomedical light source.