  We demonstrate room-temperature electroluminescence (EL) from light-emitting
diodes (LED) on highly strained germanium (Ge) membranes. An external stressor
technique was employed to introduce a 0.76% bi-axial tensile strain in the
active region of a vertical PN junction. Electrical measurements show an on-off
ratio increase of one order of magnitude in membrane LEDs compared to bulk. The
EL spectrum from the 0.76% strained Ge LED shows a 100nm redshift of the center
wavelength because of the strain-induced direct band gap reduction. Finally,
using tight-binding and FDTD simulations, we discuss the implications for
highly efficient Ge lasers.
