On the role of surface state resonances in the optical second harmonic response of Si(001)-Sb

Abstract

Optical second harmonic generation (SHG) studies of the adsorption of Sb on Si(001) are reported and compared with previous work on the Si(111)-Sb system. Measurements in ultra-high vacuum (UHV) have been made of the SH intensity in the growth region of zero to one monolayer (ML). With an excitation wavelength of 1064 nm, which produces resonantly-enhanced SHG from the clean Si(111)-7 × 7, the main effect of Sb deposition on both surfaces is seen in the 0–0.5 ML region where a large decrease in SH intensity is observed. The SH response of Si(001)-Sb and Si(111)-Sb differs considerably in this coverage range, in a way which is consistent with the known differences between the Sb adsorption sites on the two Si surfaces. At coverages above 0.5 ML, for an excitation wavelength of 634 nm, the Si(001)-Sb system shows a much larger in plane than out-of-plane SH response, indicating an increased polarisability consistent with the formation of Sb chains in the (001) surface plane.