Mean free path of photoelectrons in silicon and silicon oxides

The dependence of the mean free path λ of photoelectrons escaping from SiOx (0 ≦ x ≦ 2) on their kinetic energy and on the oxygen concentration is unclear until now. A complete theory for λ is developed, which leads to good qualitative and quantitative agreement with known experimental data for its energetic and chemical variation. It bases on the electron self-energy due to the polarization of the emitting material in the presence of excited photoelectrons and is described by longitudinal wave-vector- and frequency-dependent dielectric properties of valence and core electrons. It is shown that there exists a universal function f(x) which permits the prediction of the value of λ for an arbitrary suboxide SiOx, if, for the kinetic energy of interest, only the corresponding λ-value of Si is known. From this function the result λSiO2 = 1.4 λSi is obtained, which is approximatively independent of the electron energy.