Areal density control of ZnO nanowires in physical vapor transport using Ge nanocrystals

We revealed the most significant parameter determining an areal density of nanowires (NWs) in physical vapor transport. Seed layer characters such as the crystallinity and the surface roughness can affect the NW growth. We controlled the surface roughness and the crystallinity of seed layers both by annealing process and using Ge nanocrystals. With increase of the surface roughness of seed layers, the areal density of NWs increased, which was independent of the crystallinity of seed layers. Therefore, the large surface roughness was considered to be a critical parameter for high areal density of NWs. This study demonstrated that the substrate with well-controlled surface roughness brought control of an areal density of NWs. This well-controlled technique of NW areal density will open for the next generation NW devices.