SURFACE AND INTERFACE EFFECTS ON ELLIPSOMETRIC SPECTRA OF CRYSTALLINESI

We present the first systematic investigation of the differences among reference-quality ellipsometrically measured pseudodielectric functio n (epsilon) spectra of crystalline Si, which are nominally used to app roximate the bulk dielectric function of this material. In addition to the expected influence of residual overlayers, we identify surface-lo cal-field and energy-derivative effects, the latter representing shift s between bulk and measured critical point energies, as well as change s in excited-carrier lifetimes due to the surface. Model calculations indicate that these four effects account for nearly all differences am ong spectra studied, although a second-energy-derivative component app ears at the E-1 transition in some cases. The isotropic contribution t o the surface-local-field effect is observed for the first time. (C) 1 997 American Vacuum Society.