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

The initial growth stages of GaAs(110) thin films by molecular beam epitaxy (MBE) have been studied by scanning tunnelling microscopy (STM). For depositions at 520 degrees C up to one monolayer, STM images confirm the layer-by-layer nature of growth as indicated by reflection high energy electron diffraction (RHEED) intensity oscillations. The dynamics of island nucleation and coalescence is similar to that previously observed on GaAs(001) surfaces, with the temporal variation in surface step density giving rise to the specular RHEED oscillations. However, surfaces obtained after the deposition of sub-monolayer coverages of GaAs at 520 degrees C show a striking growth morphology. The islands adopt a characteristic triangular shape, with {113}- and {115}-type steps and the apex directed along the [001] direction. This highly specific crystallographic shape suggests that nucleations occur at the base of the triangles.