Nonlinear optical spectroscopy of silicon-boron and other silicon-adsorbate systems

Optical second harmonic generation (SHG) spectroscopy is used to study the Si(001) surface following surface deposition of B, and compared with the SHG response to deposition of H and Ge. The dramatic quenching and redshifting of SHG spectra after 1 ML hydrogen termination of both Si(001) and Ge-Si(001) surfaces clearly excludes the possibility that the main contribution of surface SHG originates from structural factor, such as strain. Boron deposition of Si(001) surface intensifies and redshifts the E₁ spectral peak, while subsequent H termination further intensifies and blueshifts E₁ in contrast to the Si(001), Ge-Si(001), and bulk B doped Si(001) surfaces. Surface reconstruction induced charge transfer between surface layers, and thus surface local electric field accounts for the observed SHG signal change and spectral shift. Ab initio pseudopotential and semi-empirical tight binding calculations reproduce these unique trends despite several approximations required to make the theoretical calculations possible.; The spectral range of nonlinear optical spectroscopy was extended by downconverting the incident femtosecond pulses to the infrared region using optical parametric amplification (OPA). SHG and sum frequency generation (SFG) spectra of Si(001) and Ge-Si(001) surfaces were measured for the extended tuning range and compared with theoretical calculations.; The effect of bulk B incorporation on the SHG spectra of Si(001) films grown by chemical vapor deposition was studied as a function of doping level and temperature. At room temperature B doping strongly enhances and blueshifts the E₁ resonance of the SHG spectra to 3.4 eV. Surface H termination reverses this effect. The observed doping and temperature dependence was successfully modeled as electric field induced SHG in the bulk depletion region. This unique sensitivity of SHG to doping suggests its great potential of SHG as an in-situ, noninvasive probe of electrically active dopants.