Properties of GaN grown at high rates on sapphire and on 6H-SiC

Thick GaN films were deposited with growth rates as high as 250 mu m/h by the direct reaction of ammonia and gallium vapor at 1240 degrees C, The characteristics of our films are comparable to those of typical thin films grown by metal organic chemical vapor deposition or molecular beam epitaxy. Grown under identical conditions, films on (0001) sapphire and on (0001) 6H-SiC were compared in terms of their structural and optical properties. Considering x-ray rocking curve full width at half-maximum (FWHM: 420 arcsec), photoluminescence linewidths of the excitons (FWHM: 3 meV at 6 K and 100 meV at 300 K), free electron concentration, defect related luminescence, and the homogeneity of these properties, we find superior values for films grown on SiC. For both substrate materials we find an optimum growth rate window of 40-80 mu m/h. (C) 1996 American Institute of Physics.