Reflectivity and reflectance anisotropy of Si(100): a polarisable bond model

Abstract

The reflectivity and reflectance anisotropy (RA) of the unreconstructed Si(100) surface are calculated using a model in which the semiconductor is a slab of polarisable bonds interacting by induced dipolar fields. Parameters for the calculations are obtained from ab initio calculations. The dielectric response of the slab is analysed in terms of dipole-moment normal modes which are called dipole waves. At the \\ ̄ gG point of the surface Brillouin zone, dipole waves are polarised either parallel or perpendicular to the surface. We find that the normal-incidence reflectivity of the dipole lattice reproduces the magnitude of the experimental reflectivity of silicon in the energy range 1–6 eV but lacks spectral features. Local fields near the surface of the slab differ from the local field in the bulk, and consequently the surface of the slab responds to optical radiation at a slightly higher frequency than the bulk, and the slab has a maximum RA of the order of 0.7%. A comparison is made between the theoretical RA spectrum and the experimental RA spectra of the Si(100)-(2 × 1) and Si(100)-(2 × 1)-As surfaces.