REFLECTIVITY AND REFLECTANCE ANISOTROPY OF SI(100) - A POLARIZABLE BOND MODEL

The reflectivity and reflectance anisotropy (RA) of the unreconstructe d Si(100) surface are calculated using a model in which the semiconduc tor is a slab of polarisable bonds interacting by induced dipolar fiel ds. Parameters for the calculations are obtained from ab initio calcul ations. The dielectric response of the slab is analysed in terms of di pole-moment normal modes which are called dipole waves. At the <(Gamma )over bar> point of the surface Brillouin zone, dipole waves are polar ised either parallel or perpendicular to the surface. We find that the normal-incidence reflectivity of the dipole lattice reproduces the ma gnitude of the experimental reflectivity of silicon in the energy rang e 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 th e surface of the slab responds to optical radiation at a slightly high er 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 x 1) and Si(100)-(2 x 1 )-As surfaces. (C) 1997 Elsevier Science B.V.