Second-harmonic generation in Si–SiO2 heterostructures formed by chemical, thermal, and plasma-assisted oxidation and deposition processes

Abstract

Second-harmonic generation (SHG) on vicinal Si(111) surfaces, ∼4° off axis, was studied by varying the chemical bonding state of the surface atoms. O-terminated surfaces were prepared by thermal oxidation, plasma deposition, and chemical oxidation. H-terminated surfaces were prepared by removing the oxide layers and subjecting the Si surfaces to RCA cleans terminated by rinses in dilute HF solutions. SHG experiments were performed in the s- and p-polarization modes, using the 1053 nm emission from a Nd:YLF laser. An angular anisotropy, characteristic of vicinal Si(111) surfaces, and including a distinctive SHG feature polarized in the [112̄] direction of the surface steps, was enhanced by the presence of an oxide layer, independent of how the Si–SiO2 interface was prepared. We show for the first time that H-terminated Si surfaces exhibited a similar angular anisotropy, and that the SHG signal polarized in the [112̄] step direction was reduced, rather than enhanced by the change in the surface bonding chemistry. Using model calculations, we illustrate that this apparent reduction in SHG signal is due to a change in the relative phase of the background and step-induced contributions to the SHG signal.