ATOMIC-STRUCTURE OF INXGA1-XAS GAAS(001) (2X4) AND (3X2) SURFACES/

We report the first atomic resolution scanning tunneling microscope im ages of the As-rich (2 x 4) and Ga-rich (3 x 2) reconstructions of Inx Ga1-xAs/GaAs(0 0 1) films (0.001 < x < 0.012) grown by metalorganic va por-phase epitaxy. The (2 x 4) phase was obtained during annealing the sample at 480 degrees C in an ultrahigh vacuum chamber. Annealing the (2 x 4) surface to 540 degrees C produced the (3 x 2) phase which con sists of single rows running parallel to the [1 1 0] direction with a spacing of 12 k The rows vary in length, being separated by defects wh ich contain As dimers. A model is proposed for the (3 x 2) which consi sts of rows of Ga dimers alternating between the first and third layer s. Since this structure exhibits a deficient of one electron, defects are required to expose As dimers in the second layer and neutralize th e surface charge. (C) 1998 Published by Elsevier Science B.V. All righ ts reserved.