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Two types of nucleation layers (NLs), including in-situ low-temperature grownGaN (LT-GaN) and ex-situ sputtered physical vapor deposition AlN (PVD-AlN), areapplied on cone-shaped nanoscale patterned sapphire substrate (NPSS). Theinitial growth process of GaN on these two NLs is comparably investigated by aseries of growth interruptions. The coalescence process of GaN grains ismodulated by adjusting the three-dimensional (3D) temperatures. The resultsindicate that higher 3D temperatures reduce the edge dislocation density whileincreasing the residual compressive stress in GaN films. Compared to the LT-GaNNLs, the PVD-AlN NLs effectively resist Ostwald ripening and facilitate theuniform growth of GaN grains on NPSS. Furthermore, GaN films grown on NPSS withPVD-AlN NLs exhibit a reduction of over 50% in both screw and edge dislocationdensities compared to those grown on LT-GaN NLs. Additionally, PVD-AlN NLsresult in an increase of about 0.5 GPa in the residual compressive stressobserved in GaN films.

Effect of Grain Coalescence on Dislocation and Stress Evolution of GaN Films Grown on Nanoscale Patterned Sapphire Substrates