Step structure on GaAs(113)A studied by scanning tunneling microscopy

The GaAs(113)A surface was prepared by molecular-beam epitaxy and in situ c haracterized by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). The occurrence of an (8 X 1) reconstruction as propose d by Wassermeier et al. [Phys. Rev. B 51, 14721 (1995)] was confirmed. Over view STM images reveal a striking anisotropy in the step structure of this surface. While steps along [33 (2) over bar] (the 1 X direction of the reco nstruction) are straight for up to 2000 Angstrom, steps along [1 (1) over b ar 0] are extremely rough. In this direction, kinks occur typically after l ess than 100 Angstrom. The ratio of the respective lateral step densities i s 8 +/- 4. This anisotropy is explained by applying the electron counting r ule (ECR) to one-dimensional islands. While islands along [33 (2) over bar] fulfil the ECR, it is violated by islands along [1 (1) over bar 0]. Thus, if structures formed additionally perpendicular to step edges along [33 (2) over bar], they would be energetically unfavorable. Hence, growth occurs m ainly by propagation along [33 (2) over bar]. It is suggested that the dete rmining structural element of GaAs(113)A - (8 X 1) is the zigzag chain of A s dimers. [S0163-1829(99)11947-7].