Single-step growth dynamics of core-shell GaN on Ga ₂O ₃ freestanding nanoprotruded microbelts

Freestanding wurtzite GaN nanoprotruded microbelts with Ga ₂O ₃ 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, Ga ₂O ₃ layers and the GaN-Ga ₂O ₃ interface are characterized by high-resolution transmission electron microscopy after focused ion beam sectioning of the belt. Initially, Ga ₂O ₃ nucleates after reaction with the O ₂ available in the environment, and subsequent reaction with NH ₃ results in the formation of core-shell structure in the catalyst-free vapor-solid growth process. Having a low-symmetry phase, Ga ₂O ₃ 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.