Reconstruction of the GaAs (311)A surface

We study the reconstruction of the GaAs (311)A surface with reflection high-energy electron-diffraction (RHEED) and scanning tunneling microscopy (STM). The surface observed in situ with RHEED during molecular-beam epitaxy is distinguished by a lateral periodicity of 3.2 nm perpendicular to the [2¯33] direction. This periodicity is confirmed employing in situ STM. High-resolution STM images furthermore reveal a surface reconstruction characterized by a dimerization of the surface As atoms. We show how the reconstruction can be formed, applying a simple electron-counting model. The excellent agreement with the experimental results further support this model, which was already found to explain the reconstructions of the (100) and the (111) surfaces. In order to form a semiconducting surface, the three uppermost layers are involved in the reconstruction process, giving rise to a depth modulation of 0.34 nm.