Gor'kov and Eliashberg Linear Response Theory: Rigorous Derivation and Limits of Applicability

A rigorous microscopic calculation of the polarizability of disordered mesoscopic particles within the grand canonical ensemble is given in terms of the supersymmetry method. The phenomenological result of Gor'kov and Eliashberg is confirmed. Thus the underlying assumptions of their method are justified. This encourages application of RMT in the Gor'kov--Eliashberg style to more complicated situations.Comment: Final published versio

Isolated oxygen defects in 3C- and 4H-SiC: A theoretical study

Ab initio calculations in the local-density approximation have been carried out in SiC to determine the possible configurations of the isolated oxygen impurity. Equilibrium geometry and occupation levels were calculated. Substitutional oxygen in 3C-SiC is a relatively shallow effective mass like double donor on the carbon site (O-C) and a hyperdeep double donor on the Si site (O-Si). In 4H-SiC O-C is still a double donor but with a more localized electron state. In 3C-SiC O-C is substantially more stable under any condition than O-Si or interstitial oxygen (O-i). In 4H-SiC O-C is also the most stable one except for heavy n-type doping. We propose that O-C is at the core of the electrically active oxygen-related defect family found by deep level transient spectroscopy in 4H-SiC. The consequences of the site preference of oxygen on the SiC/SiO2 interface are discussed

Collective versus single-particle effects in the optical spectra of finite electronic quantum systems

We study optical spectra of finite electronic quantum systems at frequencies smaller than the plasma frequency using a quasi-classical approach. This approach includes collective effects and enables us to analyze how the nature of the (single-particle) electron dynamics influences the optical spectra in finite electronic quantum systems. We derive an analytical expression for the low-frequency absorption coefficient of electro-magnetic radiation in a finite quantum system with ballistic electron dynamics and specular reflection at the boundaries: a two-dimensional electron gas confined to a strip of width a (the approach can be applied to systems of any shape and electron dynamics -- diffusive or ballistic, regular or irregular motion). By comparing with results of numerical computations using the random-phase approximation we show that our analytical approach provides a qualitative and quantitative understanding of the optical spectrum.Comment: 4 pages, 3 figure

Local-field distribution in resonant composites: Green's-function formalism

The effective response depends sensitively on composite microstructure due to large fluctuations in the local electric field. For metallic clusters embedded in a dielectric host, the local field distributions are extremely inhomogeneous in space around the metallic clusters due to quasi-static resonance, leading to a large enhancement in the effective linear and nonlinear responses. In this work, we propose a general method for computing the electric field of metallic clusters near resonance via a perturbation formalism. We illustrate the method by simple examples.Comment: 6 papges, 7 figures and PDF fil

Anharmonic vibrations of the dicarbon antisite defect in 4H-SiC

Dicarbon antisite defects were created by either electron irradiation or ion implantation into 4H-SiC. The no-phonon lines from the dicarbon antisite defect center were observed with their phonon replicas. The stretch frequencies of the defect were observed up to the fifth harmonic. The Morse potential model accounts for the anharmonicity quite well and gives a very good prediction of the vibration energies up to the fifth harmonic with an error of less than 1%. First principles calculations show that the model of a dicarbon antisite defect along with its four nearest neighboring carbon atoms can explain the observed anharmonicity

SiC Pore Surfaces: Surface Studies of 4H-SiC(1-102) and 4H-SiC(-110-2)

The morphology and atomic structure of 4H-SiC(1 (1) over bar 02) and 4H-SiC((1) over bar 10 (2) over bar) surfaces, i.e., the surfaces found in the triangular channels of porous 4H-SiC, have been investigated using atomic force microscopy, low-energy electron diffraction (LEED), and Auger electron spectroscopy (AES). After hydrogen etching, the surfaces show steps parallel and perpendicular to the c axis, yet drastically different morphologies for the two isomorphic orientations. Both surfaces immediately display a sharp LEED pattern. Together with the presence of oxygen in the AES spectra, this indicates the development of an ordered oxide. Both surfaces show an oxygen-free well-ordered surface after Si deposition and annealing. (c) 2006 American Institute of Physics.(c) 2006 American Institute of Physics

Anharmonic vibrations of the dicarbon antisite defect in 4H-SiC

Dicarbon antisite defects were created by either electron irradiation or ion implantation into 4H-SiC. The no-phonon lines from the dicarbon antisite defect center were observed with their phonon replicas. The stretch frequencies of the defect were observed up to the fifth harmonic. The Morse potential model accounts for the anharmonicity quite well and gives a very good prediction of the vibration energies up to the fifth harmonic with an error of less than 1%. First principles calculations show that the model of a dicarbon antisite defect along with its four nearest neighboring carbon atoms can explain the observed anharmonicity

Electronic states of chemically treated SiC surfaces

Electronic states at chemically treated SiC surfaces have been studied by scanning tunneling spectroscopy. Charge accumulation on the surface is deduced through a voltage shift observed in the spectra. More charge is observed on electropolished surfaces as compared to untreated (as-received) surfaces. This difference is interpreted in terms of the electropolished SiC surfaces being more insulating than as-received ones, such that on the former the transport of charge is limited and surface charges cannot come into equilibrium with the bulk semiconductor. Observations of tunneling spectra on SiC prepared by various amounts of hydrogen etching are used to support this interpretation