Uniaxially stressed germanium with fundamental direct band gap
  We demonstrate the crossover from indirect- to direct band gap in tensile-strained germanium by temperature-dependent photoluminescence. The samples are strained microbridges that enhance a biaxial strain of 0.16% up to 3.6% uniaxial tensile strain. Cooling the bridges to 20 K increases the uniaxial strain up to a maximum of 5.4%. Temperature-dependent photoluminescence reveals the crossover to a fundamental direct band gap to occur between 4.0% and 4.5%. Our data are in good agreement with new theoretical computations that predict a strong bowing of the band parameters with strain. 
R. Geiger, T. Zabel, E. Marin, A. Gassenq, J.-M. Hartmann, J. Widiez,   J. Escalante, K. Guilloy, N. Pauc, D. Rouchon, G. Os...
cond-mat.mtrl-sci physics.optics