PARALLEL VS DIAGONAL EPITAXY MODELS OF DIAMOND AND C-BN ON SI(001)

Two new structures for epitaxy of diamond and c-BN on a Si(001) substr ate, in a parallel orientation and with 3:2 registry, are proposed and also compared with a structure proposed earlier for a 45-degrees rota ted orientation of a diamond overlayer. All the models largely elimina te dangling bonds in the interface, and several variations are conside red with and without additional atoms of hydrogen or oxygen incorporat ed into the structure. The atomic geometry of each model is optimized by minimization of the total energy of periodically repeated atomic cl usters, calculated by fully self-consistent semi-empirical quantum che mical methods. It is found that the 45-degrees rotated structure is pa rticularly favourable for very thin diamond layers, but for thicker la yers the single bridge 3:2 model that works best for c-BN is also pref erred by diamond. The differences in the two materials are interpreted in terms of the way that the parallel model exploits the differences in both the size and atomic valencies of the constituent atoms in c-BN .