Surface reconstruction, screw dislocations and anisotropic step flow growth of MnAs on GaAs(1 1 1)B substrates

We have grown MnAs layers on GaAs(1 1 1)B substrates by molecular beam epitaxy and studied their morphology in situ by scanning tunneling microscopy. The surface was atomically flat with bilayer-steps and a (2×2) reconstruction on the terraces. Screw dislocations with associated growth spirals were observed. Positive and negative Burgers vectors were found with equal probability. We also observed steps with alternately smooth and jagged edges. This morphology is explained by the anisotropic growth speed of bilayer-steps.