SURFACE-STRUCTURES OF GAAS PASSIVATED BY CHALCOGEN ATOMS

When a GaAs(001) surface with Se adsorbates was flash-heated under a l ow chemical potential condition, a 2 x 3 RHEED pattern, previously rep orted as an intermediate structure, remained even after the sample was cooled. The atomic structure observed by STM is in good agreement wit h the dimer model proposed to explain the chalcogen-passivated GaAs(00 1) surfaces. Se dimers were found to be buckled, but the 2 x -periodic ity was maintained in the [110] direction, unlike the previously obser ved 4 x -structure forming the dimer row pairs. Some other structures, the axes of which are in directions different from [110], were also o bserved on the Se/GaAs(001) surface. The S-passivation effect was stud ied by measuring current-voltage properties for the S/GaAs(001) surfac e.