Single-step growth dynamics of core–shell GaN on Ga2O3 freestanding nanoprotruded microbelts

Freestanding wurtzite GaN nanoprotruded microbelts with Ga2O3 core, with typical thickness 1–10 μm, and length of few millimeters are synthesized by thermal annealing of Ga metal and subsequent reaction with ammonia at a low flow rate. They are of distinctive rectangular shape with a typical width of 10–100 μm. Thickness of the belt is about 1/10th of the width and length up to a few millimeters. The GaN, Ga2O3 layers and the GaN–Ga2O3 interface are characterized by high-resolution transmission electron microscopy after focused ion beam sectioning of the belt. Initially, Ga2O3 nucleates after reaction with the O2 available in the environment, and subsequent reaction with NH3 results in the formation of core–shell structure in the catalyst-free vapor–solid growth process. Having a low-symmetry phase, Ga2O3 can grow only in certain preferred directions thus controlling the final morphology of the belt. Nanoscale protrusions ~50–100 nm found on the surface of the belts could be an ideal system for building functional devices.