Surface structure of As-stabilized GaAs(001): 2×4,<i>c</i>(2×8), and domain structures

Abstract

Structural models characterized by missing rows of surface As dimers are proposed for the 2\ifmmode\times\else\texttimes\fi{}4 and c(2\ifmmode\times\else\texttimes\fi{}8) As-stabilized surfaces of GaAs. Experimental and theoretical support for these models and for a variable surface stoichiometry are examined. A model with full monolayer As coverage and either symmetric or asymmetric dimers is found to be inadequate. Total-energy calculations show that 2\ifmmode\times\else\texttimes\fi{}4 or c(2\ifmmode\times\else\texttimes\fi{}8) unit cells are optimal for surface As coverages of ${\ensuremath{\Theta}}_{\mathrm{As}=0.5}$ and ${\ensuremath{\Theta}}_{\mathrm{As}=0.75}$. The proposed model can account in a simple way for the observed one-dimensional disorder and provides a good description for the amplitudes of fractional-order structure factors.