Optical anisotropy of singular and vicinal Si–SiO2 interfaces and H-terminated Si surfaces

We report the first investigation of the optical anisotropy of H- and SiO2-terminated Si surfaces. We examine six different orientations: (110); several vicinal (111); (113); and vicinal (001). Observed reflectance-difference (RD) spectra fall into two classes according to whether the surface normal is oriented from [111] toward [110] or [001], being consistent with the existence of different step configurations for the two cases. In the (110) class the spectral lineshapes resemble the imaginary part of the Si dielectric function, while in the (001) class they are similar to the energy derivative of the Si reflectance spectrum. To make surface and interface comparison meaningful, we develop an analytic method for correcting interface spectra for the relatively large effects of overlayer thickness. Thickness-corrected RD spectra of Si–SiO2 interfaces are found to differ in small but distinct ways from those of H-terminated surfaces of the same orientation, specifically in the enhancement of spectral features and the appearance of an optical absorption band near 3 eV. Rapid thermal annealing between 900 and 1000 °C increases oxidation-induced interface absorption for the (113) surface and red-shifts the entire spectrum for the (110) surface. We attribute these effects to a relatively high degree of order for (110)-class steps and lower order for (001)-class steps.