Dislocation structure of GaN films grown on planar and nano-patterned sapphire

Plane view and cross-section transmission electron microscopy (TEM) images were used to compare the density, character, and curvature of dislocations developed during metalorganic vapor phase epitaxy (MOVPE) of GaN on planar c-plane sapphire with those developed during growth on nano-patterned c-plane sapphire. Scanning electron microscopy (SEM) characterization of GaN films at different stages of growth for both types of substrates complemented the TEM investigation. GaN growth on wafers patterned with an array of submicron sapphire bumps exhibited relatively uniform nucleation and initial growth, as well as early island coalescence. It is suggested that this coalescence results in a relatively small fraction of dislocations with partial screw character at the surface of the films grown on the patterned substrate, and that this may be responsible for the improvements in carrier lifetime and device efficiency seen in earlier studies on similar sapphire substrates.