Methods of growing Group-III nitride thin-film structures having reduced dislocation density are provided. Methods in accordance with the present invention comprise growing a Group-III nitride thin-film material while applying an ion flux and preferably while the substrate is stationary or non-rotating substrate. The ion flux is preferably applied as an ion beam at a glancing angle of incidence. Growth under these conditions creates a nanoscale surface corrugation having a characteristic features size, such as can be measured as a wavelength or surface roughness. After the surface corrugation is created, and preferably in the same growth reactor, the substrate is rotated in an ion flux which cause the surface corrugation to be reduced. The result of forming a surface corrugation and then subsequently reducing or removing the surface corrugation is the formation of a nanosculpted region and polished transition region that effectively filter dislocations. Repeating such nanosculpted and polished regions advantageously provide significant reduction in dislocation density in thin-film structures.