Microscopic study of surface second-harmonic generation from a clean Si(100)c(4×2)surface

Abstract

We apply a microscopic model to calculate the different contributions to the nonlinear ͑second-order͒ susceptibility required in the calculation of second-harmonic generation ͑SHG͒. These terms are classified according to 1 and 2 transitions and to the surface or bulk character of the states among which the transitions take place. As an example, we analyze the effects of these microscopic susceptibilities on the SHG spectrum of a clean Si͑100͒ c(4ϫ2) surface. Three resonances seen experimentally in SHG are analyzed through this approach. They are the E 1 resonance of bulk Si at 2ϳ3.3 eV and two others at 2ϳ2.2 and 3 eV. The physical nature of the microscopic susceptibilities calculated with our formalism allows us to understand the origin of these surface SHG resonances.