Diffusion of a Ga adatom on the GaAs(001)-\emph{c}(4 $\times$ 4)-heterodimer surface: A first-principles study

The adsorption and diffusion behavior of a Ga adatom on the $\textrm{GaAs(001)-\emph{c}(}4\times4\textrm{)}$-heterodimer surface were studied by employing ab initio density functional theory computations in the local density approximation. Structural and bonding features of the $\textrm{\emph{c}(}4\times4\textrm{)}$-heterodimer reconstruction surface were examined. A comparison with the $\textrm{\emph{c}(}4\times4\textrm{)}$-ss reconstruction\footnote{J. L. Roehl et al, Phys. Rev. B 82, 165335 (2010).} was performed. Minimum energy sites (MES) on $\textrm{\emph{c}(}4\times4\textrm{)}$-heterodimer surface were located by mapping the potential energy surface for a Ga adatom. Barriers for diffusion of a Ga adatom between the neighboring MES were calculated by using top and exchange diffusion mechanisms. We proposed two unique diffusion pathways for a Ga adatom diffusing between the global minimums of two neighboring unit cells. Signature differences between electronic structures of top- and exchange- diffusion mechanisms were studied for relevant atoms. We observed a higher diffusion barrier for exchange mechanism compared to top hopping.\footnote{Supported by NSF DMR 0705464, CNS 0855134.}