REFLECTANCE ANISOTROPY OF SILICON SURFACES - DISCRETE DIPOLE CALCULATION

The reflectivity and reflectance anisotropy (RA) spectra of five silic on surfaces [(001), (113), (112), (111), and (110)] are calculated usi ng the discrete dipole model. The structures used have bulk-terminated surfaces so that RA is found at the optical gap and above. A comparis on is made between experimental RA spectra of H-covered (001), (113), and (110) surfaces and-the discrete dipole spectra, and it is found th at there is agreement for the (001) and (110) surfaces but the best fi t to the experimental (113) surface spectrum is found for a (112) surf ace discrete dipole calculation. RA spectra are obtained using the McI ntyre-Aspnes three-layer model with surface layer and bulk dielectric functions taken from discrete dipole calculations. Surface excess diel ectric functions are shown for these surfaces. It is found that, altho ugh RA spectra of the different surfaces are quite distinct, the gross features of the surface excess dielectric functions that are used to calculate them are quite similar. Thus small shifts in maxima and mini ma and differences in strength of these functions are responsible for the observed optical anisotropy, rather than distinct spectral feature s that differ from surface to surface. The surface dielectric function converges to the bulk value within 10 to 20 Angstrom of the vacuum-so lid interface, depending on frequency, so that RA at frequencies corre sponding to the optical gap energy and above arises from this 20 Angst rom region, rather than the topmost surface layer or layers.