Abstract
We report on band-gap luminescence in strain-symmetrized, (Si/(Ge superlattices grown on a step-graded, alloy buffer with a reduced dislocation density, using Sb as a surfactant. The luminescence efficiency for a (Si/(Ge and (Si/(Ge superlattice is strongly enhanced compared with a corresponding alloy reference sample. The luminescence signals can be attributed to interband transitions of excitons localized at potential fluctuations in the superlattice. The observed systematic shift of the band-gap luminescence to lower energies with increasing period length compares well with results of a simple, effective-mass calculation. An increasing superlattice band gap and a reduction in luminescence intensity is observed if the Si and Ge layers are interdiffused by thermal annealing. The band gap for a (Si/(Ge superlattice was also measured with absorption spectroscopy. The absorption coefficient, as determined by direct transmission, is in the order of about 0.1 eV above the band gap.
- Received 25 November 1992
DOI:https://doi.org/10.1103/PhysRevB.47.4099
©1993 American Physical Society