Modulation spectroscopy at non‐normal incidence with emphasis on the vacuum‐uv spectral region

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Abstract
Expressions are given to analyze modulation spectra taken at non‐normal incidence. These expressions are used to determine the optimum angle of incidence to maximize the signal‐to‐noise ratio. Significant improvements are shown to be obtained in the vacuum‐uv spectral region by making measurements at relatively large angles of incidence. We apply these expressions to evaluate the field‐induced change in the dielectric function for the 20.5–21.0‐eV core‐level doublet in GaP from Schottky‐barrier electroreflectance data. The line shape obtained is consistent with that of a field‐modulated M0 critical point modified by a Coulomb attraction between the core hole and the excited electron.