Position-Controlled Growth of GaN Nanowires and Nanotubes on Diamond by Molecular Beam Epitaxy

In this work the position-controlled growth of GaN nariowires (NW-s) on diamond by means of molecular beam epitaxy is investigated. In terms of growth, diamond can he seen as a model substrate, providing information of systematic relevance also for other substrates. Thin Ti masks ate structured by electron beam-lithography which,allows the fabrication of perfectly homogeneous-GaN NW arrays with different diameters and distances. While the wurtzite NWS are found to be Ga-polar, N-polar nucleation leads to the forrmation of tripod structures with a zinc-blende core which can be efficiently suppressed above a substrate temperature of 870 degrees C. A variation of the III/V flux ratio reveals that both axial and radial growth rates are N-limited despite the globally N-rich growth conditions, which is explained by the different diffusion behavior of Ga and N atoms. Furthermore, it is shown that the hole arrangement has no effect on the selectivity but can be used to force a transition from nano-wire to nanotube growth by employing a highly competitive growth regime.