Dielectric constant and light emission in Si/SiO₂ superlattices

The real part of the frequency-dependent dielectric function ε₁(ω) and the light-absorption coefficient α(ω), of Si slabs confined within SiO₂ barriers have been calculated as a function of Si-slab thickness d_si. The calculation uses the imaginary part ε₂(ω) of the dielectric function obtained from tight-binding calculations. The resulting static dielectric constants are found to increase with the decreasing Si-slab width, contrary to some reported theoretical results for H-terminated Si or pure-Si clusters. The calculated integrated light absorption in the range 1.0-2.6 eV is a maximum for for slabs with d_si∼20 Å, in agreement with experimental work on light emission from Si/SiO₂ superlattices and other oxidized Si nanostructures.