In situ magnetic field-assisted low temperature atmospheric growth of GaN nanowires via the vapor-liquid-solid mechanism.

We report the growth of GaN nanowires at a low temperature of 750 °C and at atmospheric pressure in a conventional chemical vapor deposition (CVD) setup via the vapor-liquid-solid mechanism with remarkable control of directionality and growth behavior by using an in situ magnetic field. Under typical growth conditions, without any magnetic field, the nanowires are severely twisted and kinked, and exhibit a high density of planar stacking defects. With increasing in situ magnetic field strength, the microstructural defects are found to decrease progressively, and quasi-aligned nanowires are produced. At an applied magnetic field strength of 0.80 T, near-vertical aligned straight and several micrometers long nanowires of average diameter of ~40 nm with defect-free microstructure are routinely produced. Photoluminescence measurements show that the relative intensity of the defect-related peaks in the visible region with respect to the near-band-edge emission continuously decrease with increase in the applied in situ magnetic field strength, ascribable to the magnetic field-assisted significant structural improvement of the wires. It is found out that the degree of agglomerative Ni droplet on Si is critically influenced by the surface tension driven by the magnetic force, which in turn determines the eventual properties of the nanowires.