Differential reflectance and second-harmonic generation of the Si/SiO2 interface from first principles

The equilibrium atomic geometries of a Si/SiO2 interface are studied by using first principles pseudopotential method within the density functional theory. The optical linear [reflectance differential spectra (RDS)] and nonlinear [second-harmonic generation (SHG)] spectra of the Si/SiO2 interface are calculated using ab initio ultrasoft and norm-conserving pseudopotentials. Local bridgelike oxygen atomic configurations provide well defined optical features in both linear (RDS) and nonlinear (SHG) optical spectra of the Si/SiO2 interface. The results of the present work demonstrate that it is possible to unambiguously identify spectral features in both linear (RDS) and nonlinear (SHG) optical spectra of the Si/SiO2 interface with local atomic oxygen-related configurations. The advantages of a simultaneous analysis of RDS and SHG spectra are demonstrated in order to obtain a detailed picture of the Si/SiO2 interface at the atomic level.