OPTICAL 2ND-HARMONIC GENERATION SPECTROSCOPY ON SI(111)7X7

Optical second-harmonic generation from Si(111)7 x 7 has been measured as a function of pump photon energy in the range from 1.0 to 1.8 eV w ith three different combinations of incident and detected polarization directions. By representing the data by anharmonic oscillator models, resonances are found around 1.3 and 3.4 eV, and just below the limit of the spectra (0.8 eV). The 1.3-eV peak is ascribed to resonant trans itions between rest atom and adatom states while the 3.4-eV resonance is the so-called strain resonance. The origin of the peak at 0.8 eV st ill needs to be investigated.