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Unlike the Si-SiO2 interface, the SiC-SiO2 interface has large defect densities. Though nitridation has been shown to reduce the defect density, the effect of H remains an open issue. Here we combine experimental data and the results of first-principles calculations to demonstrate that a Si-C-O bonded interlayer with correlated threefold-coordinated C atoms accounts for the observed defect states, for passivation by N and atomic H, and for the nature of residual defects.

Oxidation of SiC produces SiO2 while CO is released. A 'reoxidation' step at lower temperatures is, however, necessary to produce high-quality SiO2. This step is believed to cleanse the oxide of residual C without further oxidation of the SiC substrate. We report first-principles calculations that describe the nucleation and growth of O-deficient C clusters in SiO2 under oxidation conditions, fed by the production of CO at the advancing interface, and their gradual dissolution by the supply of O under reoxidation conditions. We predict that both CO and CO2 are released during both steps.PACS numbers: 68.55. Ln, 68.35.Dv The most significant property of semiconductors is their ability to sustain heterogeneous n-type and p-type doping. This property, however, is eroded by high temperatures and high voltages that cause intrinsic excitation of electron-hole pairs across the band gap. As a result, semiconductors with significantly larger band gaps than silicon have been investigated as candidates for electronic devices suitable for high temperatures and high voltages. Silicon carbide is a particularly attractive candidate because its native oxide is SiO 2 which works so well as a dielectric in Si-based microelectronics. The presence of a third element, however, namely C, results in a wide range of phenomena that do not occur in the Si-SiO 2 system. In particular, oxidation of SiC entails the production of CO which effuses through the oxide [1,2]. Afanas'ev et al. have suggested that carbon clusters at and near the interface form during oxidation [3,4], but the structure and dynamics of these clusters has not been established. Lipkin and Palmour found that, after oxidation, a 'reoxidation' step is necessary to produce high-quality oxides and SiC-SiO 2 interfaces [5,6]. During this step, oxygen is supplied as during oxidation, but the temperature is lowered so that no further oxidation takes place. In contrast, post-oxidation heat treatment without the supply of O leads to an increase of charged defects in the oxide [7]. It is believed that the 'reoxidation' step cleanses the interface and bulk SiO 2 of residual carbon [3]. Duscher et al. recently presented direct experimental evidence for the existence of carbon in as-grown samples and its removal after reoxidation [8].The nucleation and growth of impurity clusters in semiconductors is a generic problem for which totalenergy calculations are well suited to provide detailed information. In this Letter we present the results of extensive first-principles density-functional calculations that allow us to give a detailed account of the nucleation and growth of O-deficient carbon clusters in SiO 2 during oxidation conditions and their dissolution during reoxidation conditions. Basically, a CO molecule, generated at the advancing interface and diffusing through the oxide, can bind weakly to an O site in the SiO 2 network. A second CO molecule, however, can bind to the first and the new complex is very stable. Additional CO molecules can extend the cluster. The process is ...

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Nitrogen incorporation at the SiO2/SiC interface via high temperature nitric oxide annealing leads to the passivation of electrically active interface defects, yielding improved inversion mobility in the semiconductor. However, we find that such nitrided oxides can possess a larger density of hole traps than as-grown oxides, which is detrimental to the reliability of devices (e.g., can lead to large threshold voltage instabilities and to accelerated failure). Three different charge injection techniques are used to characterize this phenomenon in metal–oxide–semiconductor structures: x-ray irradiation, internal photoemission and Fowler–Nordheim tunneling. Some nitrogen-based atomic configurations that could act as hole traps in nitrided SiO2 are discussed based on first-principles density functional calculations.

We investigate the static and dynamic behaviors of a Br adlayer electrochemically deposited onto single-crystal Ag(100) using an off-lattice model of the adlayer. Unlike previous studies using a lattice-gas model, the off-lattice model allows adparticles to be located at any position within a two-dimensional approximation to the substrate. Interactions with the substrate are approximated by a corrugation potential. Using Density Functional Theory (DFT) to calculate surface binding energies, a sinusoidal approximation to the corrugation potential is constructed. A variety of techniques, including Monte Carlo and Langevin simulations, are used to study the behavior of the adlayer. The lateral root-mean-square (rms) deviation of the adparticles from the binding sites is presented along with equilibrium coverage isotherms, and the thermally activated Arrhenius barrier-hopping model used in previous dynamic Monte Carlo simulations is tested.

With extensive first-principles calculations, we investigated the geometric structure, phase transition, and electronic properties of orthorhombic, monoclinic, and tetragonal K 1x Na x NbO 3 (KNN) as functions of the Na content. We found that KNN undergoes an orthorhombic-to-monoclinic-to-orthorhombic phase transition when the Na content is gradually increased. We also found that the polarization vector of the monoclinic phase can be rotated more easily than those of the orthorhombic and tetragonal phases, giving rise to an enhanced piezoelectric response of the monoclinic KNN. Furthermore, our calculations provide an interpretation for the experimentally observed unusual broad peak of the KNN piezoelectric parameters.S. B. Sinnott-contributing editor Manuscript No. 35030.