X. F. Hu

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#

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.

Ex-situ and in-situ probing of Column IV interfaces using optical second harmonic generation

Using femtosecond pulses from a Kerr-lens Mode-Locked Ti:Sapphire laser to generate second harmonic from a series of native-oxidized Si(001)/SiO2 samples prepared with systematically varied etch- induced interfacial microroughness, we demonstrate rapid, noncontact, noninvasive measurement of Angstrom-level Si(001)/SiO2 interface roughness. These measurements were performed in air and correlated with atomic force microscopy (AFM) measurements. We also demonstrate in-situ second harmonic monitoring of Si epitaxy in two growth regimes: high temperature (approximately equals 925 K) ultra high-vacuum chemical vapor deposition (UHV-CVD) growth mode and a cyclic atomic layer epitaxy (ALE) growth mode. During UHV-CVD growth of Si on ALE-grown Si0.9Ge0.1(001), we observed interference of the second harmonic signals between the growing Si surface and the buried Si0.9Ge0.1(001) interface. In the ALE growth mode, we monitored several key stages during a full cycle of growth of a partial (approximately equals 0.42) Si monolayer on Si(001) from a disilane (Si2H6) precursor.

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.

Femtosecond ellipsometry and surface second-harmonic probes of Ge, Si1-xGex, Si, and diamond

We demonstrate two complementary techniques: femtosecond ellipsometry and surface second harmonic generation, for characterization and diagnostics of semiconductor epilayers using unamplified femtosecond laser sources. Through femtosecond ellipsometry, we obtained the time-resolved change in the real and imaginary parts of the index of refraction in relaxed and strained Si1-xGex alloys. Through surface second harmonic generation in conjunction with the Kerr Lens mode-locked (KLM) Ti:Sapphire laser, we obtained surface second harmonic signals in Si(100) and Diamond(111) with an unprecedented signal-to-noise ratio.