The mechanism of dc-electric-field-induced second-harmonic generation ͑EISH͒ was studied at the buried Si͑111͒-SiO 2 interface in transmission through a planar Si-SiO 2 -Cr MOS structure. The second-harmonic contribution of the field-induced quadratic polarization generated in the space-charge region is determined. The role of the spatial distribution of the dc electric field inside the silicon space-charge region is demonstrated, as well as the influence of the oxide thickness. We have developed a phenomenological model of the EISH taking into account the interference between field-dependent and field-independent contributions to the nonlinear polarization ͑nonlinear interference͒ as well as the retardation of the EISH wave. We show that, due to these interference effects, the minima of the EISH curves do not coincide with the flatband voltage.

Epitaxial PbZrxTi1−xO3 (PZT) films have been prepared by metalorganic chemical vapor deposition on SrTiO3 substrates. Two sets of films of thicknesses 50–100 and 700–1400 nm, containing 0%, 40%, 60%, and 100% Zr, were prepared and investigated. The refractive index n was determined by ellipsometry for the thin films and by reflectivity for the thicker films. Results were obtained over the energy range from 1.55 to 3.72 eV, and with a Cauchy-fit extrapolation down to 0.62 eV. The refractive-index curves show a systematic variation with composition. For all compositions, n is close to 3.2 at 3.72 eV (333 nm), while at 1.55 eV (800 nm) n is 2.35 for PZ (x=1) and 2.61 for PT (x=0). In agreement with previous results we find that the optical band gap is essentially independent of composition for PZT. We obtained 3.6±0.1 eV. The n(E) results were analyzed by a Wemple–DiDomenico dispersion analysis, yielding results for the dispersion region in the ultraviolet. Unlike the band gap, which is insensitive to composition in PZT, the dispersion energy Ed decreases from PT to PZ in the same fashion as the refractive index in the transparent region.

Spectroscopic electric-field-induced second harmonic generation on a Si(111)-SiO2-C r metal-oxide-silicon structure shows a bias-independent " interface" resonance at 3.25 eV and a ''bulk'' resonance at 3.43 eV which is strongly bias dependent. The symmetry forbidden bulk dipole contribution becomes observable, and even dominating, due to the bias-induced band-bending that breaks the bulk inversion symmetry. The origin of these resonances is discussed, as well as the prospects for using second harmonic generation as a probe of metal-oxide-silicon characteristics.

Recently a number of second-harmonic-generation (SHG) experiments on (thick) oxide films on Si were performed as studies of the possible presence of strain, crystalline Si0 2 , a static electric field, and roughness at the S i-S i0 2 interface. Large enhancements of the SHG anisotropy have been observed for thick oxide films. We show here that the SHG for thick thermal oxide films on S i ( ll l) as a function of oxide thickness and angle of incidence is dominated by linear optics, owing to multiple reflections in the oxide film.

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