Buffer-layer-free growth of high-quality epitaxial GaN films on 4H-SiC substrate by metal-organic chemical vapor deposition

High-quality GaN epitaxial films were successfully grown directly on 4H-SiC substrates. The difficulty in the nucleation as well as the overgrowth of GaN islands, which is often observed during metal-organic chemical vapor deposition, was solved using the concept of an epitaxial lateral overgrowth technique. The continuous mirror-flat GaN epitaxial film could be obtained at a reduced reactor pressure (76 Torr) and a lower N/Ga supply ratio. The full-width half-maximums (FWHMs) of the (0 0 0 2) and (1 0 1¯ 3) rocking curves of the GaN epitaxial films on the 4H-SiC substrate at the optimized condition were 105 and 118 arcsec, respectively, under a skew symmetric diffraction geometry. The intense bound exciton lines with a FWHM of 10 meV and a free exciton peak appeared in the low-temperature photoluminescence spectrum, illustrating the very high quality of the GaN film on 4H-SiC.