Electroreflectance spectroscopy of strained Si1−xGex layers on silicon

Electroreflectance spectroscopy was used to measure the direct transitions in strained Si1−xGex layers in the energy range from 3–6 eV. We were able to detect the transitions E1, E1 + Δ1, E′0, E0, E0 + Δ0, E2(X), E2(Σ) and E′1 for multiple samples with germanium concentrations from 12.5–28.1% for temperatures from 10–300 K. The transitions E1 + Δ1, E0, E0 + Δ0, E2(Σ) and E′1 were detected for the first time in strained Si1−xGex layers and it was also the first investigation of the temperature dependence of direct transitions in strained Si1−xGex. Good agreement with theoretical calculations of strain shifts was found for the E0 transition, while deviations occur for the E1 transition.