Temperature dependences of the ${\mathit{E}}_0$ transitions in bulk Ge and a Ge-rich (Si${)}_{\mathit{m}}$/(Ge${)}_{\mathit{n}}$ superlattice

Using photoreflectance (PR) spectroscopy, the temperature dependences of the ${\mathit{E}}_0$ transition in bulk Ge and a (Si${)}_{\mathit{m}}$/(Ge${)}_{\mathit{n}}$ strained-layer superlattice (SLS) were measured at temperatures from 87 to 295 K. A rapid decrease in the PR amplitude with temperature was observed for the SLS as compared with the bulk Ge ${\mathit{E}}_0$ transition. This decrease is explained by using a model relating the PR amplitude to minority-carrier lifetime. The overall temperature dependences of the measured PR amplitudes were found to be consistent with the assumptions of this model. The model implies that there may be a different trapping mechanism in the superlattice than in bulk Ge. Fits to the Varshni relation also indicate a different temperature dependence of the ${\mathit{E}}_0$ transition energies in the SLS as compared with bulk Ge. The measured bulk germanium Varshni coefficients are found to be in reasonable agreement with the results of an earlier determination.