Abstract
We present atomically resolved scanning tunneling micrographs of the surfaces of GaAs(001) films grown by metalorganic vapor-phase epitaxy (MOVPE). Thin films deposited in an MOVPE reactor were transferred to an (ultra high) vacuum system without air exposure. After heating the samples from 480 to 580°C, high-quality images of the (2 × 4)/c(2 × 8), (1 × 6)/(2 × 6) and (4 × 2)/c(8 × 2) reconstructions were obtained. In addition, a new Ga-rich (3 × 2)/(3 × n) phase was observed that forms during annealing at 540°C. This structure consists of single dimer rows running along the [110] direction with a spacing of 12 Å. The rows vary in length, and are separated by line defects which occur on average every 20 Å ( n = 5). 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 deficit of one electron, line defects are required to expose As dimers in the second layer and neutralize the surface charge.
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