Bulk and surface contributions to resonant second-harmonic generation from Si(001) surfaces

The spectra of the isotropic and anisotropic contributions to second-harmonic generation from modified Si(001) surfaces are separated using polarization selection and rotational anisotropy. A bulk, anisotropic resonance is observed at a two-photon energy of 3.42 +/- 0.01 eV. The isotropic surface contributions for native oxide Si and thermal oxide, Si show peaks at 3.39 +/- 0.01 eV and 3.35 +/- 0.01 eV, respectively. Interference between these contributions and the bulk signal can shift the apparent resonance position if they are not separated. The surface produces a noninterfering contribution that is comparable to the interfering contribution for H-terminated. Si but negligible for oxidized silicon. (C) 2002 American Institute of Physics. [DOI: 10.1063/1.1533122].