Effect of gate oxidation method on electrical properties of metal-oxide-semiconductor field-effect transistors fabricated on 4H-SiC C (0001) face Appl.The key stages of the dry oxidation of the SiC͑0001͒ surface are analyzed based on first-principles calculations. It is found that an abrupt SiC/ SiO 2 interface model results in a large activation barrier of oxygen penetration to the silicon carbide, and thus the penetration is probably the rate-limiting step for the entire dry-oxidation process. The subsequent reactions of SiC oxidation after oxygen penetration are investigated, and it is found that CO release is competing with carbon dimer formation. These dimers probably are responsible for near-interface traps in the silica layer generated during SiC oxidation. The possible passivation reactions of a carbon dimer defect by active species, such as O 2 , NO, and H 2 are investigated. It is found that an oxygen molecule can break a Si-C bond via dissociation in the triplet state and finally can produce two CO molecules from the carbon dimer defect. The NO molecule can easily break a Si-C bond of a carbon dimer defect and form cyano groups -CN, which can finally recombine to form a C 2 N 2 molecule. This molecule can hardly diffuse in silica matrix, and it is suggested that it is further oxidized by an NO molecule to CO and N 2 molecules. It is suggested that the process of passivation by O 2 and NO molecules is restricted by the incorporation of these molecules in small voids near the carbon defect. Based on the calculated results, a simple kinetic mechanism of dry SiC oxidation is proposed and kinetic modeling of the oxidation process is performed. It is found that in the framework of this mechanism, the carbon defect density should weakly depend on temperature.

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Using first-principles calculations we investigated the oxidation properties of model Pt∕HfO2 interfaces as a function of oxygen partial pressure. A wide range of interfacial oxygen concentrations were explored, varying from an oxygen-free interface to the case of 1 oxygen ML separating the Pt(111) slab from the first Hf plane in the monoclinic HfO2(001) slab. In all cases the interfaces were optimized using ab initio molecular dynamics. It was found that 1 ML of oxygen at the Pt∕HfO2 interface is only possible for chemical potentials equivalent to an oxygen pressure of tens of bars. With respect to silicon oxidation only the oxygen-free interface is stable. Depending on the anneal conditions, intermediate concentrations of ~0.25 or ∼0.75 ML of oxygen at the interface are possible, while the concentration of 0.5 ML is only stable over a narrow range of conditions. The band offset and work of separation were calculated for Pt∕HfO2 interfaces as a function of the oxygen concentration at the interface. The valence band offset drops sharply with increasing oxygen chemical potential, from ∼3.0 to ∼1.0 eV. The same trend is observed for the work of separation, which decreases from ∼6 J∕m2 for an oxygen-free interface to ∼1 J∕m2 for one oxygen monolayer. These findings may shed new light into recent experimental data reporting exceedingly small values for the effective work function of Pt on HfO2 and its dependence on the oxygen partial pressure during high temperature annealing.

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The quantum-chemical simulation (DFT, PBE, TZ2p basis set) of the mechanism of catalytic hydrogenation of compounds containing R(n)X --> O semipolar bonds (R(n)X = N(2), Me(2)S, C(5)H(5)N, Ph(3)P) on the Wilkinson catalyst (Ph(3)P)(3)RhCl with para-hydrogen showed that this process proceeds with retention of proton nuclear spin correlation, which enables a principal possibility to synthesize para-H(2)O, i.e. the nuclear spin isomer of water with antiparallel proton spins, using this route.

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