Two-step growth procedure for homogeneous GaN NW arrays on graphene

Growth of GaN nanowires (NWs) on graphene substrates is carried out by plasma-assisted molecular beam epitaxy. We test a two-step growth procedure consisting of a first stage at relatively low temperature followed by a second stage at higher temperature. We investigate the impact of this process on the usually long incubation time which precedes the first GaN nucleation events on graphene. We also examine how the selectivity of growth between graphene and the surrounding SiO₂surface is affected. After optimization of this procedure, it is applied to the growth of GaN NWs on a graphene layer patterned by electron beam lithography. A clear advantage of the two-step growth is observed in terms of reduction of the incubation time and improvement of height uniformity.