INITIAL-STAGE OXIDATION OF THE GE-SI(111)-(5X5) AND GE-SI(111)-(7X7) SURFACES

We have grown Ge:Si (111) epitaxial structures using low temperature photochemical vapor deposition. The electronic proper-ties and initial stage oxidation of the reconstructed surfaces of these grown structures have been investigated with ultraviolet photoelectron spectroscopy, ion scattering spectroscopy, and low-energy electron diffraction. We find that the initial surface oxidation is a two-step process: formation of molecular precursors followed by dissociation into atomic species. Transition from the first step to the second step can be induced by thermal annealing or light irradiation. Surface oxidation is strongly affected by the local electronic structures. Oxygen reacts preferentially with adatoms on these reconstructed (7 x 7) and (5 x 5) surfaces, and changes in the top surface Ge/Si ratio result in drastic change in oxygen uptake rate.