On the growth mechanisms of GaAs nanowires by Ga-assisted chemical beam epitaxy

GaAs nanowires (NWs) growth kinetics by Ga-assisted chemical beam epitaxy on Si(111) substrates is studied as a function of the initial Ga catalyst dimensions and growth parameters such as substrate temperature and V/III flux ratio. The preparation method for substrates is optimized in order to obtain a surface oxide with a thickness around 0.5 nm, allowing the decomposition of Ga metalorganic precursor and the preferential growth of GaAs NWs at the oxide pinholes. The successful self-formation of Ga droplets over the slightly oxidized Si surface has been observed by scanning electron microscopy (SEM), whose initial size is demonstrated to affect both the NW growth rate and the resultant NW aspect ratio. NW morphology is thoroughly analyzed by SEM, showing a self-organized array of vertically aligned match-shaped GaAs NWs with a hexagonal footprint. In addition, the crystalline structure of NWs is monitored in-situ by reflection high-energy diffraction (RHEED), showing pure zincblende phase along the whole NW stem.