Abstract
High-quality GaN epitaxial films have been grown on sapphire by organometallic vapor phase epitaxy using multiple-pair buffer layers. Each pair of buffer layers consists of a thin GaN nucleation layer grown at a low temperature around 500 °C and a thick GaN epitaxial layer around 4 μm thick grown at a high temperature around 1000 °C. The sample with four-pair buffer layers showed much improved GaN epitaxial films, as compared to the sample with only one-pair of buffer layers. The better qualities include narrower full width at half maximum of 150 arc-s and stronger intensity in double-crystal X-ray diffraction, higher electron mobility of 420 cm 2 V-s -1 , lower background concentration of 3×10 17 cm -3 , and lower etch-pit density of mid-10 5 cm -2 .