Crystalline to amorphous transition and band structure evolution in ion-damaged silicon studied by spectroscopic ellipsometry Evidence of near-surface localization of excited electronic states in crystalline SiWe present the first systematic investigation of the differences among reference-quality ellipsometrically measured pseudodielectric function ͗⑀͘ spectra of crystalline Si, which are nominally used to approximate the bulk dielectric function of this material. In addition to the expected influence of residual overlayers, we identify surface-local-field and energy-derivative effects, the latter representing shifts between bulk and measured critical point energies, as well as changes in excited-carrier lifetimes due to the surface. Model calculations indicate that these four effects account for nearly all differences among spectra studied, although a second-energy-derivative component appears at the E 1 transition in some cases. The isotropic contribution to the surface-local-field effect is observed for the first time.

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