Si/Ge superlattice embedded in silicon and germanium: electronic structure and transition probabilities

Abstract

We study a five-period Si 4/Ge 4 superlattice embedded in a 40 layer silicon spacer ((Si 4/Ge 4) 5(Si) 40) and a five-period Si 4/Ge 6 superlattice embedded in a 48-layer germanium spaced ((Si 4/Ge 6) 5(Ge) 48). Results concerning the band structure, spatial behaviour of the electronic states, transition energies and transition probabilities are presented. The calculated optical transition matrix elements show that the first transition with an appreciable value is between superlattice states for the case of (Si 4/Ge 4) 5(Si) 40 and between germanium states for (Si 4/Ge 6) 5(Ge) 48. The latter result is in agreement with recent experimental observations. In addition we calculate the imaginary part of the dielectric function for (Si 4/Ge 4) 5(Si) 40 and compare it with that of the Si 4Ge 4 superlattice.