THE NATURE OF ISLAND FORMATION IN THE HOMOEPITAXIAL GROWTH OF GAAS(110)

The initial growth stages of GaAs(110) thin films by molecular beam ep itaxy (MBE) have been studied by scanning tunnelling microscopy (STM). For depositions at 520 degrees C up to one monolayer, STM images conf irm the layer-by-layer nature of growth as indicated by reflection hig h energy electron diffraction (RHEED) intensity oscillations. The dyna mics of island nucleation and coalescence is similar to that previousl y observed on GaAs(001) surfaces, with the temporal variation in surfa ce step density giving rise to the specular RHEED oscillations. Howeve r, surfaces obtained after the deposition of sub-monolayer coverages o f GaAs at 520 degrees C show a striking growth morphology. The islands adopt a characteristic triangular shape, with {113}- and {115}-type s teps and the apex directed along the [001] direction. This highly spec ific crystallographic shape suggests that nucleations occur at the bas e of the triangles.