ATOMIC-STRUCTURE CALCULATIONS FOR EPITAXY OF C-BN ON SI(001)

Several models with different topologies for the atomic structure in t he interface between a Si(001) substrate and an epitaxial c-BN(001) ad film are investigated. The models represent 3:2 parallel epitaxy as we ll as epitaxy associated with an adsorbate structure rotated by 45-deg rees relative to the substrate. Variations including hydrogen and oxyg en atoms in the interface are also considered. For each model the atom ic positions are optimised using a quantum chemical total energy calcu lation with periodic repetition of clusters, containing up to 8 atomic layers. The most favourable 3:2 model has an interface energy of 2.01 eV/1 x 1 substrate surface unit cell (SSUC), slightly more favourable that the 2.13 eV/SSUC of the best 45-degrees rotated model. This rela tive advantage increases with the film thickness due to a smaller epit axial mismatch for 3: 2 models. The calculated energetics indicates th at the most favourable of the investigated interface structures should be able to sustain an epitaxially grown adsorbate of up to 90 atomic layers without the need for stress reducing defects.