Effects of Initial Thermal Cleaning Treatment of a Sapphire Substrate Surface on the GaN Epilayer

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Abstract
We investigated the effects of the in situ thermal cleaning treatment of a (0001) sapphire substrate surface in hydrogen ambient on the structural, optical, and electrical properties of epitaxial GaN films grown by metalorganic chemical vapor deposition (MOCVD). Hall effect, X-ray diffraction (XRD), and photoluminescence measurements of GaN films grown at 1040°C clearly indicate that the film quality is strongly affected by the thermal cleaning treatment of the substrate surface. GaN films under the optimized thermal cleaning treatment at 1070°C for 10 min showed minimum full-widths at half maximum (FWHMs) of 273 arcsec and 728 arcsec for (002) and (102) XRD peaks, respectively. In addition, the FWHM of the band-edge emission peak was as narrow as 28.3 meV, and the intensity ratio between the band edge emission and the yellow band emission was as high as 100 at room temperature. It was also found that the roughness of sapphire surface was reduced after the thermal treatment.