Temperature dependences of the E0 transitions in bulk Ge and a Ge-rich (Si)m/(Ge)n superlattice

Using photoreflectance (PR) spectroscopy, the temperature dependences of the E0 transition in bulk Ge and a (Si)m/(Ge)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 E0 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 E0 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.