INTERPRETATION OF CRITICAL-POINT ENERGY SHIFTS IN CRYSTALLINE SI BY NEAR-SURFACE LOCALIZATION OF EXCITED ELECTRONIC STATES

Various surface-optical spectra can be described in terms of energy de rivatives of the bulk dielectric function. The spectra unequivocally i ndicate that critical point energies obtained from optical data are no t necessarily equal to bulk values and that surface chemical and struc tural terminations are at least contributing factors. We invoke locali zation and transition-lifetime arguments to describe these effects. Ex isting surface-optical calculations do not address these contributions , which may explain in part why discrepancies remain between theory an d experiment. (C) 1998 Elsevier Science S.A.