Microstructure and micro-Raman studies of nitridation and structure transition of gallium oxide nanowires

Here we present a detailed study on nitridation and structure transition in monoclinic gallium oxide (β-Ga2O3) nanowires grown on Si substrates with chemical vapor phase epitaxy. The nanowires were systematically nitridated at different temperatures. Their morphologies and microstructures were precisely characterized using field-emission scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and confocal micro-Raman spectroscopy. It is found that heat treatment of Ga2O3 nanowires in the gas of ammonia results in rich substructures including the Ga2O3 phase, the crystalline GaN phase, and other meta structures. The identification of these structures helps to understand some interesting phenomena observed in nanostructures, such as the microstructural origin of the unknown Raman lines in GaN nanowires. ► Nitridation and structure transition of Ga2O3 significantly depend on temperature. ► GN bonds form at lower temperatures but the Ga2O3 lattice is still dominant. ► Amorphous GaN coexists with crystalline Ga2O3 at higher temperatures. ► Crystalline GaN with distinct morphology is obtained at much higher temperatures.