GaAs(001) surface under conditions of low As pressure: Evidence for a novel surface geometry

Using density-functional theory we identify a new low-energy structure for GaAs(001) in an As-poor environment. The discovered geometry is qualitative ly different from the usual surface-dimer based reconstructions of III-V se miconductor (001) surfaces. The stability of the new structure, which has a c(8 x 2) periodicity, is explained in terms of bond saturation and favorab le electrostatic interactions between surface atoms. Simulated scanning tun neling microscopy images are in good agreement with experimental data, and a low-energy electron diffraction analysis supports the theoretical predict ion.