Ga–As dimer structure for the GaAs(0 0 1)-c(4×4) surface

We studied the atomic structure of the As-stabilized GaAs(0 0 1)-c(4×4) surface using scanning tunneling microscopy, reflection high-energy electron diffraction, reflectance difference spectroscopy, and first-principles calculations. The structure model consisting of three Ga–As dimers per c(4×4) unit cell explains well the experimental data. The three Ga–As dimers in the c(4×4) unit cells are usually aligned in the same orientation, which was found to be energetically stable. We also discuss the possible change to the symmetric As–As dimer structure under more As-rich condition.