Electroluminescence from strained germanium membranes and implications for an efficient Si-compatible laser

We demonstrate room-temperature electroluminescence (EL) from light-emitting diodes (LEDs) 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 100 nm redshift of the center wavelength because of the strain-induced direct band gap reduction. Finally, using tight-binding and finite-difference time domain simulations, we discuss the implications for highly efficient Ge lasers.