dc-electric-field-induced and low-frequency electromodulation second-harmonic generation spectroscopy ofSi(001)−SiO2interfaces

Abstract

The mechanism of DC-Electric-Field-Induced Second-Harmonic (EFISH) generation at weakly nonlinear buried Si(001)-SiO 2 interfaces is studied experimentally in planar Si(001)-SiO 2 -Cr MOS structures by optical secondharmonic generation (SHG) spectroscopy with a tunable Ti:sapphire femtosecond laser. The spectral dependence of the EFISH contribution near the direct two-photon E 1 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 function formalism which takes into account all retardation and absorption effects of the fundamental and second harmonic (SH) waves, optical interference between field-dependent and field-independent contributions to the SH field and multiple reflection interference in the SiO 2 layer. Good agreement between the phenomenological model and our recent and new 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 MOS structures. PACS numbers: 42.65.Ky, 73.65.Qv, 68.35.-p Optical Second Harmonic Generation (SHG) has been one of the most intensively studied phenomena in surface and interface optics [1-3] for the last decade. The interest in SHG stems from its unique sensitivity to the structural and electronic properties of surfaces and interfaces of centrosymmetric media. This unusually high surface/interface-sensitivity comes about because, in the electric dipole approximation, SHG is forbidden in the bulk of materials with inversion symmetry [4,5], but allowed at interfaces, where inversion symmetry is broken by the discontinuity of crystalline structure. Related nonlinear sources of SHG are localized in a thin (several nanometers thick) surface or interface layer. In semiconductors, inversion symmetry is also broken by the DC-electric Field (DCF) in the subsurface Space Charge Region (SCR), which is created by initial band bending and/or external bias application. The lack of inversion symmetry in the SCR results in DC-Electric-Field Induced Second-Harmonic (EFISH) generation, which manifests itself through electromodulation of the SHG intensity. Thus, all important properties of surfaces, buried interfaces and subsurface layers -their charge [6-8], electronic surface state density [9-11], roughness (morphology) [12,13], adsorption (adatom and admolecule surface density) [14-17], initial band bending [18-20], etc. -can, in principle, be determined by means of the SHG probe. The technological importance of ...

Optical Second Harmonic Generation in Semiconductor Nanostructures

“…First, the CSHG intensity spectrum was compared with the EFISH that was measured on p-Si(001) [17] (Figure 2). One can see that EFISH spectrum shows a maximum at 2Dω ≈ 3.34 eV that is close to the E 1 resonance in silicon.…”

Bond models in linear and nonlinear optics

“…www.pss-b.com electric-field-induced second-harmonic (EFISH) [30] effects. Diffraction was considered, and the types of patterns resulting from Gaussian-beam excitation were explained.…”

Optical rectification and Pockels effect as a method to detect the properties of Si surfaces

“…Local electric-field-induced (EFI) second-order nonlinear optical effects, such as EFI SHG [11,12] , EFI PE, and EFI OR [13][14][15] , were observed. EFI SHG and EFI second-harmonic spectroscopy have been widely used for characterization of Si-SiO 2 interfaces in metal-oxide-semiconductor (MOS) devices [16][17][18][19][20][21][22][23][24] . In these investigations, researchers mainly focused on Si(111) or Si(001) surfaces, and there have been very few papers on the nonlinear optical effects of Si(110) surfaces.…”

“…[18][19][20] for the EFI OR also was used in this work. If the azimuth with respect to the x axis of the linearly polarized light is θ, the dc polarization along the z axis (namely the [110] orientation) can be expressed as …”