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 bulk transitions. The splitting between the surface E1 and 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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