Controlled formation of oxide shells from GaN nanowires: Poly- to single-crystal

One-dimensional nanocable heterostructures consisting of GaN nanowire cores and Ga₂O₃ shells were prepared by thermal oxidation of single-crystal GaN nanowires in an oxygen atmosphere. Morphologically uniform GaN/Ga₂O₃ core/shell nanocable structures with single-crystal oxide shells can be obtained in a controllable manner by varying the oxygen pressure and oxidation time. Although the thickness of the oxide shell can be controlled by varying the oxidation time and oxygen pressure, the crystallinity of the oxide shell evolves from a single crystal to a polycrystal as the oxygen pressure is increased. This behavior implies that the process can be understood in terms of the competition between the diffusion of oxygen through the growing oxide layer and the reaction at the GaN/Ga₂O₃ interface.