Structural properties of GaN epilayers on wet-etched protruding and recess-patterned sapphire substrates were investigated in detail using high-resolution double-crystal X-ray diffraction and etch-pit density methods. The double-crystal X-ray diffraction results revealed various dislocation configurations on both types of patterned sapphire substrate. The etch pits of GaN on the recess patterned sapphire substrate exhibited a regular distribution, i.e. less etch pits or threading dislocation density onto the recess area than those onto the sapphire mesas. On the contrary, an irregular distribution was observed for the etch pits of GaN on the protruding patterned sapphire substrate. A higher crystal quality of the GaN epilayer grown onto the recess patterned sapphire substrate could be achieved as compared with that onto the protruding patterned sapphire substrate. These data reflect that the GaN epilayer on the recess patterned sapphire substrate could be a better template for the second epitaxial lateral overgrowth of GaN. As a result, the GaN epilayers after the epitaxial lateral overgrowth process displayed a threading dislocation density of around 106/cm2.

Defect Reduction of Laterally Regrown GaN on GaN/Patterned Sapphire Substrates. D.S.Wuu, H.W.Wu, S.T.Chen, T.Y.Tsai, X.Zheng, R.H.Horng: Journal of Crystal Growth, 2009, 311[10], 3063-6