Ultrafast growth of horizontal GaN nanowires by HVPE through flipping the substrate

Recently, horizontal nanowires (NWs) have attracted much attention due to their increased compatibility with NW-based integrated nanoelectronic and nanophotonic systems. However, it still remains challenging to synthesize horizontal NWs efficiently. Here we introduce a novel method towards controllable growth of horizontal GaN NWs using HVPE with an Au/Ni thin film as the catalyst. By simply flipping the substrate, horizontal GaN NWs with various growth directions and cross sections have been obtained on a sapphire substrate with various facet orientations. Benefiting from the high decomposition frequency of GaCl precursors, the growth rate for the horizontal NWs is as fast as 400 μ h-1. Our results show that the facing orientation of the loaded substrate affects the flow of the local precursor, which determines the growth mode of the GaN NWs, i.e., no matter whether the substrate is facing downward or upwards. Photoluminescence measurements of the horizontal NWs show a finite blue shift of the band edge-related emission. It indicates the presence of compressed stress and is confirmed by the geometrical phase analysis (GPA) further. Our work opens up a new route and sheds light on the horizontal GaN NWs and will advance the development of horizontal NW-based nanoelectronic and nanophotonic devices and systems.