Process-induced strain bandgap reduction in Germanium nanostructures

We studied the photoluminescence of tensile strained germanium nanostructures. Sub-micron gratings and pillars were fabricated before being coated with strained silicon nitride films. Using different deposition conditions and different sizes of structures the stress in the nanostructures can be controlled. The measured optical properties of the samples show that the direct band-gap is shifted drastically towards higher wavelengths over 1.9 μm. This local control of the stress in germanium nanostructures opens the route for both emitters and photodetectors above 1.6 μm wavelength which are not easily available and also potentially towards a germanium laser.