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

Structural models characterized by missing rows of surface As dimers are proposed for the 2×4 and c(2×8) 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 2×4 or c(2×8) unit cells are optimal for surface As coverages of ${\Theta }_{\mathrm{As}=0.5\mathrm{}}$ and ${\Theta }_{\mathrm{As}=0.75\mathrm{}}$. 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.