Influence of growth rate on the structure of thick GaN layers grown by HVPE

Thick GaN films grown by hydride vapour phase epitaxy have been investigate d by cathodoluminecsence, X-ray diffraction, and photoluminescence. Cross-s ectional studies of thick GaN layers grown on sapphire without buffers reve al three zones: a highly disordered interface region; a columnar defective region and a good quality main region of the layer. The influence of the hi ghly doped columnar region on the surface morphology and crystal structure of the layers has been studied. We show that the columnar region influences the material quality more strongly in thinner films. Thicker layers exhibi t improved morphology with lower surface pit density and better crystal qua lity shown in photoluminescence and X-ray diffraction spectra. The relation ship between the near-interface columnar structures and surface pits is rev ealed. A strong effect of the growth rate on the structure of thick layers is found. The results suggest that GaN layers with optimum crystalline qual ity may be obtained by varying the growth rate during growth. (C) 2000 Else vier Science B.V. All rights reserved.