Tensile strained Ge membranes

Germanium membranes of 50-1000 nm thickness have been fabricated by a combination of epitaxial growth on a Si substrate and simple etching processes. The biaxial tensile strain in these membranes has been measured by high-resolution X-ray diffraction and by ultrasonic vibrational spectroscopy. The later technique also shows that membranes have a Q-factor of ~3000 at low temperature. The stain in these membranes is extremely isotropic and the surface is observed to be very smooth, with an rms roughness of below 2 nm. The process of membrane fabrication also serves to remove the misfit dislocation network that originally forms at the Si/Ge interface, with benefits for the mechanical, optical and electrical properties of the crystalline membranes.