Abstract
The orientation dependence of oxygen adsorption was studied by AES and LEED using a cylindrical GaAs sample which exposes the low index orientations (001̄), (111̄), (110), (111), and (001) as well as all intermediate orientations on its surface. For the sample prepared by ion bombardment (IB) only, the adsorption is strong and nearly orientation independent. After ion bombardment and annealing (IBA), the oxygen adsorption on (001), (001̄) and (111̄) still is comparatively strong due to the influence of residual defects. In the range (331̄)-(110)-(111)-(113), a strong orientation dependence is observed which can be understood in terms of enhanced adsorption on edge adjacent sites. When the surface is prepared by molecular beam epitaxy (MBE), the overall amount of adsorbed oxygen is reduced indicating smaller defect concentrations. Also the orientation dependence becomes weaker. LEED observations show that in this case the regions between most of the low index orientations show only weak indications for steps but strong facetting which greatly reduces the edge site concentration. Obviously MBE promotes the formation of low index facets representing the state of lowest surface energy. However, in the range (110)-(111)-(112), also after MBE stable steps are formed which near (110) are two (110)-layers high.
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