Low Temperature Photoluminescence Study of Silicon-Germanium Alloy Superlattices

摘要

Low temperature photoluminescence studies were performed on nine silicongermanium alloy superlattice samples. The luminescence spectra showed sharp peaks in the 0.95 to 1.05 eV energy range, and a broad band located 0.05 to 0.12 eV below the alloy bandgap. The sharp peaks were identified as transitions associated with impurity bound excitons. The linewidth was about 10 times that in pure silicon; in addition, the peaks shifted to lower energy as the sample temperature was raised from 1.4 to 15 K. These features were attributed to effects of random distribution of atoms in the alloy. The broad band shifted to lower energy as the temperature was raised and also narrowed considerably in bandwidth. This broad luminescence was attributed to recombination of excitons confined in potential wells created by local fluctuations in the alloy composition.