Photoluminescence studies on ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$ layers exceeding the critical thickness show not only dislocation-related D1, . . ., D4, but also in addition a broad band (T band), centered at ∼110 meV below the strained alloy band gap. Depth profiling studies show that the T band is due to centers in the ${\mathrm{Si}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Ge}}_{\mathit{x}}$. The excitation power dependence and high quantum efficiency of the T band can be explained by assuming that it is due to an isoelectronically trapped exciton. T-band line shapes were fitted by a model based on statistical fluctuations of the Ge content and their effect on the local gap energy.

• Received 28 May 1993

DOI:https://doi.org/10.1103/PhysRevB.48.18276