OXIDATION OF CLEAN AND H-TERMINATED SIC SURFACES

The oxygen uptake on H-terminated and on differently reconstructed, cl ean 3C-SiC(001) and 6H-SiC(001) surfaces was investigated by X-ray pho toelectron spectroscopy (XPS). The samples were cleaned in ultrahigh v acuum (UHV) by heating them in the presence of a Si flux at different temperatures. H-terminated surfaces were prepared by exposure to hydro gen atoms in the UHV-system. Atomic hydrogen was produced by thermal d issociation of H-2-molecules at a tungsten filament heated to 2200 K. Clean and H-terminated surfaces were exposed to research grade oxygen in the range of 10(13)-10(28) O-2-molecules cm(-2). During exposures a ny excitations of the surface or the gas were avoided. The uptake of o xygen on clean surfaces proceeds in two subsequent steps. We attribute the first one to dissociative chemisorption which saturates at about one monolayer. The second process follows an inverse-logarithmic growt h law and we describe it by field-assisted oxidation, i.e. the Mott-Ca brera mechanism. On H-terminated surfaces, the initial sticking coeffi cient is reduced by a factor of approximately 10(10). (C) 1997 Elsevie r Science S.A.