The preparation of hexagonal ͕0001͖ 4H and 6H silicon carbide surfaces by hydrogen plasma or etching in hydrogen flow produces highly ordered monolayers of silicon dioxide. Their structure and epitaxial relationship to the SiC substrate were analyzed by quantitative low-energy electron diffraction and Auger electron spectroscopy. The bond angles and distances retrieved agree with those of bulk SiO 2 . Due to the saturation of all dangling bonds the semiconductor surface is passivated and

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... es its perfect order also in air. The practically ideal oxide monolayers may serve as a seed for growing epitaxial oxides with low defect density and only few structural distortions at the interface to the SiC substrate.