Dynamics of As Atoms in the Reconstruction Layer of the As-rich GaAs(001) c(4x4) Surface

摘要

The dynamics of As atoms in the reconstruction layer of the As-rich GaAs(001) c(4x4) surface is studied by molecular dynamics calculations with the semi-empirical PM3 formalism. The surface As atoms have, as expected, increased vibrational amplitudes compared to the bulk. In addition, large anisotropies exist between vibrational amplitudes normal vs. parallel to the surface and also between the [-1,1,0] vs. [1,1,0] surface directions. The signs of these anisotropies are opposite at high (～900K) and low (～500K) temperatures, where the MBE growth of stoichiometric (High-Temperature-) and non-stoichiometric (Low-Temperature-) GaAs is usually performed, respectively. As a consequence, these anisotropies cause, at low temperature growth, a rather high As surface concentration (desorption reduced) and, due to the increased in-plane vibrations an enhanced surface diffusion, particularly in the [1,1,0] direction. The anisotropy of the surface diffusion offers a model to explain the experimentally observed dependence of excess As formation during growth on substrate surfaces tilted away from the (001) orientation.