Visible Emission from a Dense Biexciton Gas in SiGe/Si Quantum Wells under External Anisotropic Strain

The effect of external anisotropic strain on the infrared and visible luminescence spectra of SiGe/Si quantum well heterostructures at liquid helium temperatures is investigated for the first time. It is shown that, at a temperature of T = 5 K, the stretching of the SiGe layer along the 100] direction leads to an increase in the relative intensity of the visible luminescence by a factor of 7/3 ? 2.3. This effect is absent when the sample is stretched along the 110] direction. These observations are explained by considering “bright” and “dark” biexciton states involved in multiparticle recombination. At a temperature of 2 K, the relative intensity of the visible luminescence increases upon stretching by a factor of 3.4–3.9, which may indicate either the splitting of the ground states of biexcitons with different electron configurations or the deviation of their distribution function from the Boltzmann law.