Atomic structure of InxGa1−xAs/GaAs(0 0 1) (2×4) and (3×2) surfaces

We report the first atomic resolution scanning tunneling microscope images of the As-rich (2×4) and Ga-rich (3×2) reconstructions of InxGa1−xAs/GaAs(0 0 1) films (0.001<x<0.012) grown by metalorganic vapor-phase epitaxy. The (2×4) phase was obtained during annealing the sample at 480°C in an ultrahigh vacuum chamber. Annealing the (2×4) surface to 540°C produced the (3×2) phase which consists of single rows running parallel to the [1 1 0] direction with a spacing of 12 Å. The rows vary in length, being separated by defects which contain As dimers. A model is proposed for the (3×2) which consists of rows of Ga dimers alternating between the first and third layers. Since this structure exhibits a deficient of one electron, defects are required to expose As dimers in the second layer and neutralize the surface charge.