Nucleation and growth from GaN pre-nuclei: role of the Ga/GaN interface structure

Understanding the atomic-scale mechanisms governing metal-mediated growth of gallium nitride (GaN) and related alloys is critical for tailoring their structural and functional properties in advanced electronic, optoelectronic, and quantum devices. Using real-time environmental transmission electron microscopy (E-TEM), we elucidate the NH₃-assisted GaN nucleation and growth from Ga droplet arrays with and without GaN pre-nuclei. For the lowest temperatures, although GaN nucleation at Ga droplet arrays is not observed, GaN growth occurs preferentially at pre-existing GaN nuclei, presumably due to the reduced Gibbs free energy for NH₃ decomposition at Ga/GaN interfaces. Meanwhile, for intermediate to high temperatures, E-TEM reveals nucleation and growth of GaN from Ga droplets with and without GaN nuclei. Interestingly, for the arrays of Ga droplets with wurtzite GaN nuclei, rapid, discontinuous conversion of Ga to GaN is observed. On the other hand, for the arrays of Ga droplets with zincblende GaN nuclei, layer-by-layer growth of GaN is apparent.  We consider the role of the Ga/GaN interface in facilitating NH₃ decomposition and crystallization of GaN.  We also discuss the influence of the GaN pre-nuclei polytypes on subsequent GaN growth kinetics. Together, these real-time visualizations offer fundamental insights into metal-mediated nucleation and growth of GaN and related materials.