RECONSTRUCTIONS OF THE GAAS(111)B SURFACE

The (111)B surface of GaAs has been investigated using scanning tunnel ling microscopy (STM) and a number of different reconstructions have b een found at different surface stoichiometries. In accordance with ele ctron diffraction studies, we find the series (2 X 2), (1 X 1)(LT) (ro ot 19 X root 19) and (1 X 1)(HT) with increasing annealing temperature , corresponding to decreasing surface As concentration. We find the (1 X 1)(LT) to be a mixture of the local structures of the (2 X 2) and ( root 19 X root 19) phases as well as some elements of a (3 X 3) struct ure. This is behaviour consistent with a system, dominated by the supp ly of As adatoms to the surface, and may be an example of a continuous phase transition. Above the (1 X 1)(LT) transition, atomic resolution images of the (root 19 X root 19) surface reveal only a threefold sym metry of the hexagonal structural units, brought about by inequivalent surface bonding. This is responsible for the disorder found in the (r oot 19 X root 19) reconstruction, since the structure may form in one of two domain rotations. At lower surface As concentration, the (1 X 1 )(HT) surface adopts a random structure containing small domains of a (root 7 X root 7)R19.1 degrees reconstruction. (C) 1998 Elsevier Scien ce B.V.