Abstract

Ge surfaces have been investigated with optical second-harmonic generation (SHG) spectroscopy in the range from 1.78 to 3.44 eV. The spectra reveal surface-specific resonances corresponding to the E1 and $\mathrm{E}1+{\mathrm{\Delta }}_1$ bulk transitions. The splitting between the surface E1 and $\mathrm{E}1+{\mathrm{\Delta }}_1$ resonances is found to be larger than the bulk value. It is suggested this is caused by surface-induced band bending through a Rashba effect. By probing metal-oxide-semiconductor structures it is found that contributions from electric-field-induced SHG from the space charge region are negligible for Ge within the probed spectral range. Strong second-harmonic resonances in the 2.6–3.2 eV range are observed and tentatively assigned to Ge–Ge bonds at the interface.

© 2013 Optical Society of America

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