High-Temperature Growth of GaN Nanowires by Molecular Beam Epitaxy: Toward the Material Quality of Bulk GaN

In molecular beam epitaxy, the spontaneous formation of GaN nanowires on Si(111) substrates at elevated temperatures is limited by the long incubation time that precedes nanowire nucleation. In this work, we present three growth approaches to minimize the incubation time and to thus facilitate significantly higher growth temperatures (up to 875 °C). We achieve this advancement by (i) using III/V flux ratios of >1 to compensate for Ga desorption, (ii) introducing a two-step growth procedure, and (iii) using an AlN buffer layer to favor GaN nucleation. The GaN nanowire ensembles grown at so far unexplored substrate temperatures exhibit excitonic transitions with sub-meV linewidths comparable to those of state-of-the-art free-standing GaN layers grown by hydride vapor phase epitaxy.