Analysis of reflectance difference spectra of Si(001)(2 x 1):As/Sb surfaces

We compute the surface dielectric function anisotropy (SDA) and reflectance-difference (RD) spectra of Si(001)(2 x 1):As/Sb surfaces. The calculations are based on the local density approximation (LDA) scheme and utilize a novel set of basis functions, which are the products of plane waves in the surface planes and localized Gaussian functions in the direction normal to the surface. We identify and interpret the SDA and RD spectra in terms of interband transitions, and find that these transitions are mainly related to the electronic surface bands and surface-induced bands. Considering that the calculations based on the LDA of density functional theory (DFT) usually underestimate the band gaps for semiconductors, we make the many-body self-energy correction by shifting the related energy bands and then calculate the dielectric function anisotropy and reflectance difference spectra. We also take into consideration the excitonic and local field effects with a contact-potential model. The final fitted result for Si(001)(2 x 1):As surface is in reasonable agreement with experimental observations. (C) 1999 Elsevier Science B.V. All rights reserved.