Abstract: A gallium nitride-based structure includes a substrate, a first layer of gallium nitride disposed on a growth surface of the substrate, and a second gallium nitride layer disposed on the first gallium nitride layer. The first layer includes a region in which a plurality of voids is dispersed. The second layer has a lower defect density than the gallium nitride of the interfacial region. The gallium nitride-based structure is fabricated by depositing GaN on the growth surface to form the first layer, forming a plurality of gallium nitride nanowires by removing gallium nitride from the first layer, and growing additional GaN from facets of the nanowires. Gallium nitride crystals growing from neighboring facets coalesce to form a continuous second layer, below which the voids are dispersed in the first layer. The voids serve as sinks or traps for crystallographic defects, and also as expansion joints that ameliorate thermal mismatch between the Ga.N and the underlying substrate.