Nonlinear optical susceptibility of the (111) and (001) surfaces of silicon

Abstract

The nonlinear optical susceptibility χ(2) for second-harmonic generation at the (111) and (001) surfaces of silicon is studied in the framework of the self-consistent tight-binding theory. Equilibrium atomic structures of the (001) and (111) surfaces of silicon are determined by minimizing the total energy of the system. To achieve a better description of the conduction band of bulk silicon, a peripherals* state is added to the minimalsp3 tight-binding basis. The electron-electron and electron-ion Coulombscreened interactions are included by solving the secular equation self-consistently. The dependence of the χ(2) spectra on the atomic structure of the surfaces of silicon is investigated. Intensive response of χ(2) is found in the spectral regions corresponding to optical transitions involving surface states. Optical structures of χ(2) which correspond to the directE1 andE2 gaps in silicon are also found. The results obtained are discussed in comparison with the data available in the literature.