Structural Modulation of GaN Nanowires Grown in High-Density Plasma Environment

We demonstrate a structural modulation method of GaN nanowires (NWs) by microwave plasma chemical vapor deposition. This method is based on the self-assembled growth mode without a harmful gas source and could easily achieve structures with a remarkable range of geometries and sizes by regulating the plasma-phase conditions. The results show that we are able to modulate GaN NWs with a large scale of sizes of lengths from ∼2.2 to 52.4 μm and diameters from ∼22 to 1000 nm. Due to introduce the high-density plasma phase, we propose a new growth and modulation model of GaN NWs via combining the competition and equilibrium of the interface effect, the diffusion effect, and the surface effect. We found that the critical diameter defined by the surface energy has a noteworthy correlation with the growth of NWs due to the significant effect of nitrogen plasma on the surface of NWs. In addition, the photoluminescence performance including the emission peak position, intensity, and full width at half-maximum can be well regulated by the structural effects of GaN NWs. This modulation provides an economical, flexible, and environmentally friendly route to single-crystalline GaN NWs and their devices. Furthermore, the combined growth effect model could provide new physical and chemical insight into the growth mechanism of GaN NWs controlled by high-density plasma.