M. H. Anderson

dc-electric-field-induced and low-frequency electromodulation second-harmonic generation spectroscopy of Si(001)-SiO2 interfaces

The mechanism of dc-electric-field-induced second-harmonic ~EFISH! generation at weakly nonlinear buried Si(001)-SiO2 interfaces is studied experimentally in planar Si(001)-SiO 2-Cr MOS structures by optical second-harmonic generation spectroscopy with a tunable Ti:sapphire femtosecond laser. The spectral dependence of the EFISH contribution near the direct two-photon E1 transition of silicon is extracted. A systematic phenomenological model of the EFISH phenomenon, including a detailed description of the space-charge region ~SCR! at the semiconductor-dielectric interface in accumulation, depletion, and inversion regimes, has been developed. The influence of surface quantization effects, interface states, charge traps in the oxide layer, doping concentration, and oxide thickness on nonlocal screening of the dc-electric field and on breaking of inversion symmetry in the SCR is considered. The model describes EFISH generation in the SCR using a Green’s-function formalism which takes into account all retardation and absorption effects of the fundamental and second-harmonic ~SH! waves, and multiple reflection interference in the SiO 2 layer. The optical interference between field-dependent and -independent contributions to the SH field is considered as aninternal homodyne amplifier of the EFISH effects. Good agreement between the phenomenological model and our EFISH spectroscopic results is demonstrated. Finally, low-frequency electromodulated EFISH is demonstrated as a useful differential spectroscopic technique for studies of the Si-SiO 2 interface in silicon-based metaloxide-semiconductor structures. @S0163-1829~99!01836-6#

Femtosecond carrier-induced screening of dc electric-field-induced second-harmonic generation at the Si(001) SiO(2) interface.

Carrier-induced screening of the dc electric field at the Si(001)-SiO(2) interface is observed by intensity-dependent and femtosecond-time-resolved second-harmonic spectroscopy. The screening occurs on a time scale of ~?(p)(-1) , the reciprocal plasma frequency of the generated carriers.

Fourth-harmonic generation at a crystalline GaAs(001) surface

We demonstrate fourth-harmonic generation from a GaAs(001) surface by using femtosecond pulses well below damage threshold. Our data reveal a strong fourfold anisotropic surface-specific polarization that is not present in second-harmonic generation and is nearly as strong as the bulk polarization.

D.c. electric field induced second-harmonic generation spectroscopy of the Si(001)–SiO2 interface: separation of the bulk and surface non-linear contributions

D.c. electric field induced second-harmonic generation (SHG) spectroscopy of the Si(001)–SiO2 interface was studied both experimentally and theoretically. To describe the experimental results the general phenomenological model of d.c. induced SHG in centrosymmetric semiconductors is developed, taking into account surface and bulk field dependent as well as field independent contributions to the non-linear polarization. The solution of an inverse problem within this model of d.c. induced SHG allows all surface and bulk contributions to the non-linear response from an Si(001)–SiO2 interface to be distinguished.

Size effects in second harmonic generation from Si(001)-SiO2 interface: microscopic interface effects and optical Casimir nonlocality

Size effects in optical second harmonic generation (SHG) from Si(001)-SiO2 planar micro-cavity structures are studied for fundamental wavelengths from 700 nm to 850 nm. The observed dependence of SHG intensity on the thickness of oxide layer is explained, in part, by an optical Casimir nonlocality arising from interference of zero-point fluctuations in micro-cavity, which is distinguished from microscopic interface effects. Detailed theoretical analysis of the Casimir nonlocal contribution to the quadratic susceptibility using a diagrammatic technique is performed for visible and IR regions. The difference in the length scale of the Casimir contribution at 800 nm and 1064 nm fundamental wavelength is discussed.

dc-Electric-field-induced and Low-frequency Electromodulation Second-harmonic Generation Spectroscope

Summary form given. The second-harmonic generation (SHG) has been one of the most intensively studied phenomena in surface and interface optics for the last decade due to its unique sensitivity to the structural and electronic properties of surfaces and interfaces of centrosymmetric media. A dc electric field breaks the inversion symmetry of the centrosymmetric semiconductor in the space-charge region (SCR) and induces the bulk dipole nonlinear polarization at the SHG frequency, which is governed by the cubic susceptibility.

New directions in surface spectroscopy enabled by ultrafast lasers

Solid state femtosecond lasers enable powerful new nonlinear optical spectroscopic characterization techniques for technologically relevant Column IV and III-V semiconductor interfaces and growth surfaces.

Applications of Femtosecond Lasers to Nonlinear Spectroscopy and Process Control of Si(001) Interfaces

Solid state femtosecond lasers are providing a powerful new nonlinear optical spectroscopic characterization tool for technologically relevant buried SiO2/Si(001) interfaces and Si1-xGex(001) epitaxial growth surfaces.