SCANNING-TUNNELING-MICROSCOPY OF THE GAAS (311)A SURFACE RECONSTRUCTION

Reflection high-energy electron diffraction (RHEED) and scanning tunne ling microscopy (STM) are used to study the reconstruction of the GaAs (311)A surface. During and after molecular-beam epitaxy, in-situ RHEE D of the surface shows a lateral periodicity of 3.2 nm perpendicular t o the [2 $($) over bar$$ 33] direction. This periodicity is confirmed employing in-situ STM. The height of this periodic surface structure i s two monolayers, i.e., 0.34 nm. We show how this reconstruction, char acterized by a dimerization of the surface As atoms, can be formed usi ng a simple electron counting model. The excellent agreement with the experimental results further support this model, that was already foun d to explain the reconstructions of the (100) and (111) surfaces.