Abstract
A new vacancy-complex model for the (2×2) reconstructed As-stabilized (1¯ 1¯ 1¯) surface of GaAs in which the surface bilayer contains two As and three Ga atoms per unit cell is proposed. Half the surface As atoms occupy stacking-fault sites, leading to nearly optimal rehybridizations of surface-bonding orbitals. The surface As coverage is consistent with both mass spectrometry and Auger data. The calculated surface electronic structure is nonmetallic and provides a satisfactory description of polarization-dependent angle-resolved photoemission data.