Direct observation by transmission electron microscopy of the influence of Ni catalyst-seeds on the growth of GaN–AlGaN axial heterostructure nanowires

A study of GaN–AlGaN nanowire heterostructures grown by molecular beam epitaxy on sapphire substrates is presented. Nanowire growth was promoted using nickel seeds formed by in-situ annealing of a Ni thin film. Deposition sequences were designed to form two nanowire samples with embedded alternating multilayers of GaN and Al0.2Ga0.8N of variable thicknesses. Subsequent analyses showed the formation of two types of nanostructures in both samples, namely long and tapered nanowires and short columnar structures with uniform diameters along the whole length.