Step structure on $\mathrm{GaAs}\mathrm{}\left(113\right)A$ studied by scanning tunneling microscopy

The $\mathrm{GaAs}\mathrm{}\left(113\right)A$ surface was prepared by molecular-beam epitaxy and in situ characterized by scanning tunneling microscopy (STM) and low-energy electron diffraction (LEED). The occurrence of an $(8\mathrm{}\times 1)$ reconstruction as proposed by Wassermeier et al. [Phys. Rev. B 51, 14 721 (1995)] was confirmed. Overview STM images reveal a striking anisotropy in the step structure of this surface. While steps along $\left[332¯\right]$ (the 1× direction of the reconstruction) are straight for up to 2000 Å, steps along $\left[11¯0\right]$ are extremely rough. In this direction, kinks occur typically after less than 100 Å. The ratio of the respective lateral step densities is $8\pm 4.$ This anisotropy is explained by applying the electron counting rule (ECR) to one-dimensional islands. While islands along $\left[332¯\right]$ fulfil the ECR, it is violated by islands along $\left[11¯0\right].$ Thus, if structures formed additionally perpendicular to step edges along $\left[332¯\right],$ they would be energetically unfavorable. Hence, growth occurs mainly by propagation along $\left[332¯\right].$ It is suggested that the determining structural element of $\mathrm{GaAs}\mathrm{}\left(113\right)A-(8\mathrm{}\times 1)$ is the zigzag chain of As dimers.