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.