Highly selective dry etching of germanium over germanium-tin (Ge(1-x)Sn(x)): a novel route for Ge(1-x)Sn(x) nanostructure fabrication.

We present a new etch chemistry that enables highly selective dry etching of germanium over its alloy with tin (Ge(1-x)Sn(x)). We address the challenges in synthesis of high-quality, defect-free Ge(1-x)Sn(x) thin films by using Ge virtual substrates as a template for Ge(1-x)Sn(x) epitaxy. The etch process is applied to selectively remove the stress-inducing Ge virtual substrate and achieve strain-free, direct band gap Ge0.92Sn0.08. The semiconductor processing technology presented in this work provides a robust method for fabrication of innovative Ge(1-x)Sn(x) nanostructures whose realization can prove to be challenging, if not impossible, otherwise.