Influence of substrate material, orientation, and surface termination on GaN nanowire growth

In this work, we investigate the fundamental role of the substrate material, surface orientation, and termination on GaN nanowire (NW) nucleation and growth. First of all, the use of a patterned a-Si/diamond substrate confirms that NW shape and dimension are mainly determined by the applied growth conditions instead of the nature of the substrate. More important is the surface orientation as it defines growth direction and epitaxial relationship towards the GaN NWs, where both (111) and (100) surfaces yield NW growth for equivalent growth conditions. (110) substrates are found to be not suited for NW growth. Finally, the surface termination of diamond is demonstrated to survive the employed growth conditions and, therefore, to affect the nucleation of nanowires and the electronic properties of the heterointerface by its surface dipoles. This difference in nucleation is exploited as an alternative approach for selective area growth without deposition of a foreign mask material, which might also be transferable to other substrates.