Study of radial growth in patterned self-catalyzed GaAs nanowire arrays by gas source molecular beam epitaxy

Ordered arrays of vertically aligned self-catalyzed GaAs nanowires have been grown by gas source molecular beam epitaxy (GS-MBE) on silicon substrates using nano-patterned oxide templates. Several growth processes of different duration were performed under identical conditions and with identical sample preparation. To determine the influence of pattern parameters, the samples were prepared with 20 patterned areas, each with progressively increasing hole diameters and pitch. Measurements of the average lengths and diameters of the vertically oriented nanowire areas were then used to calculate the overall axial and radial growth rates. These experiments confirm that significant accompanying radial growth occurs. Furthermore, the rate of radial growth increases with increasing pattern pitch. We propose that gallium-rich conditions may increase the size of the liquid droplet, resulting in an inverse tapered morphology which promotes step-flow radial growth via secondary adsorption on the nanowire sidewalls. The pitch dependence of the radial growth rate may therefore be due to shadowing or competition for the flux of material desorbing from the oxide surface between the nanowires. ((c) 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)