Quantum-chemistry study of semiconductor systems: The initial oxidation of the (111)Si-H surface

We propose a well-defined procedure to adapt a Quantum-Chemistry technique for the study of semiconductor structures. The procedure comprises use of a Bloch-periodic version of the standard molecular code and a nanocrystal cluster model. We reparametrize according to this procedure the MNDO/AM1 technique for Si and O and present this new parametrization AM1/Crystal. We apply AM1/Crystal to study oxidation of the hydrogenated silicon(111) surface, at the initial stages, when the absorbed oxygen atoms form isolated surface defects. We obtain self-consistent charge distributions and total energies for optimised geometries of different incorporation sites and configurations, including up to three oxygen atoms. We also obtain vibrational frequencies for the complexes that compare well with available experimental data. Our results confirm that backbond incorporation (Si-O-Si-H) is energetically favored compared to a surface hydroxyl configuration (Si-OH) and indicate that the first subsurface layer incorporation should proceed by island formation in a two-dimensional regime.