Photoluminescence of Si-rich Si-Ge alloys

A detailed study of the photoluminescence spectrum of ${\mathrm{Si}}_{1-x}{\mathrm{Ge}}_x$ is presented for $x\approx 0.1$. Undoped and In-doped alloy samples are investigated. Spectral features are identified, and the effects of the disordered nature of the alloy on the luminescence spectrum are discussed. In particular, mechanisms for the observed broadening of bound-exciton luminescence are discussed, and the shift in alloy luminescence energy is obtained. At low temperatures a luminescence feature is observed which may result from recombination of excitons bound to local fluctuations in alloy composition.