DIAMOND EPITAXY ON A SI(001) SUBSTRATE - A COMPARISON OF STRUCTURAL MODELS

A previous proposal for the atomic structure at the interface of a dia mond (001) adfilm growing epitaxially on Si(001) in a 45 degree rotate d orientation, is extended by the inclusion of Si atoms in the second adfilm layer. In addition, two new models for growth in 3:2 registry i n a parallel orientation are investigated, including versions with and without incorporation of hydrogen atoms into the structure. For each model, a total energy optimisation of the geometry is carried out usin g quantum chemical calculations with the PM3 Hamiltonian applied to pe riodically repeated atomic clusters containing up to eight atomic laye rs. Due to the non-stoichiometric nature of the interface layers, comp arisons of the relative energetics of the models are performed by the introduction of carefully defined interface and adhesive bonding energ ies. It is found that the rotated model has a very low intrinsic inter face energy and is favourable for very thin adfilms, but due to the sm aller elastic deformation needed for registry the parallel growth mode becomes most favourable for thicker layers. Detailed atomic geometrie s for the optimised structures of all three models are given.