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The initial oxidation processes on both the C-face and Si-face SiC surfaces are investigated by performing electronic-structure calculations within the density functional theory. We find the characteristic features of stable structures and adsorption-desorption behavior depending on the surface orientation of SiC. The desorption of C atoms as CO molecules on the C-face occasionally occurs in addition to the adsorption of O atoms even for the surfaces with low oxygen coverage, whereas the adsorption of O atoms preferentially occurs on the Si-face. These calculated results indicate that the incorporation of O atoms along with the desorption of C atoms is predominant even during the initial oxidation processes on the C-face of SiC. Moreover, on the C-face, three-coordinated O atoms can be formed at the topmost layer of the SiC surface, resulting in the formation of SiO 2like layers whose characteristics are different from those on the Si-face. These findings suggest that the differences in carbon-desorption behavior and resultant structural difference of SiO 2 layers between the C-face and the Si-face are possible origins of the orientation dependence of oxidation rate observed in SiC oxidation.

The formation processes of InN/GaN heterostructures on GaN(0001) substrate are investigated by means of our ab initio-based approach and Monte Carlo (MC) simulations. Our ab initio calculations reveal that even under Ga-rich conditions the pseudo-(1×1) surface consisting of In in the first layer and Ga in the second layer is more stable than that of Ga in the first layer and In in the second layer. Furthermore, the calculated surface phase diagrams demonstrate that the pseudo-(1×1) surface with In-Ga metal layers can incorporate 2.3 monolayers (MLs) of N atoms under growth conditions. The MC simulations using ab initio calculation data imply that both InGaN alloy and InN/GaN heterostructure can be formed depending on the growth conditions, consistent with the experimental results. On the basis of these findings, the stability of these structures is discussed in terms of the strain accumulation in the resultant structures.