Nucleation and growth of gallium arsenide on silicon

We have studied the early stages of growth of GaAs on Si (001), misoriented by 4° towards [110], by migration-enhanced epitaxy (MEE) in a molecular beam epitaxy (MBE) system. We present results using in situ and ex situ analyses, reflection high-energy electron diffraction (RHEED), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray photoelectron diffraction (XPD) and X-ray double crystal diffractometry (DCD) performed at each stage of growth. We show that the nucleation by MEE induces a surface roughness decreasing as the layer becomes thicker. XPD experiments at the onset of the growth show a stoichiometric GaAs without antiphase domains. The relaxation of stress for the layers deposited at low temperature (300°C) occurs via partial dislocation migration developing between them, stacking faults and microtwins. The post annealing of films with thicknesses less than 60 nm drives the formation of three-dimensional islands on the silicon surface. These islands develop (114) facets in the [11¯0] direction where the Ga migration is greater. The height over the base ratio of these islands is uniform and from Bauer's relation, we calculate the interface energy which can be correlated to the strain energy due to the dislocations near the interface. There are two reasons for the restruction of the surface. First, from a thermodynamical approach including surfaces and interface energies of the GaAs/Si system, we can demonstrate that the growth of GaAs/Si is a three-dimensional Volmer-Weber growth. Second, the bulk energy due to the compressive strain of a continuous pseudomorphic GaAs film is higher than that of an islanding GaAs where relaxation from the free surfaces of the islands occurs. The post annealing of films with thickness higher than 60 nm has a smoothing effect and can give a perfect two-dimensional (001) surface. Growth at higher temperatures (580°C) suppresses plane defects, creates a Lomer dislocation network at the interface and induces the 60° dislocations in the bulk. We perform X-ray DCD experiments on 90 nm thick layers. We observe, before annealing a compressive biaxial stress of about −1.9×108Pa which is the driving force for the elimination of the plane defects.