Effect of the temperature gradient between a substrate and its ambient on the growth of vertically-aligned GaN nanorods

In a hot-wall reactor for hydride vapor phase epitaxy (HVPE), the substrate holder was specially designed in such a way that the substrate temperature was much lower than its ambient because of an additional cooling mechanism, and GaN nanorods were grown on these air-cooled substrates. From these experiments, both the substrate temperature itself and the temperature gradient between the substrate and its ambient were found to be critical parameters in the growth of GaN nanorods. In addition, synchrotron X-ray scattering revealed that the GaN nanorods did not contain the cubic phase commonly observed in GaN films grown at low temperatures.