The crystal structure and surface morphology of hydride vapour phase epitaxy grown thick (12-105 mum) GaN layers have been investigated as a function of growth rate using several structure sensitive techniques like atomic force microscopy (AFM), x-ray diffraction (XRD) in omega-2heta and omega-rocking curve measurements as well as low temperature photoluminescence (PL). PL and XRD measurements reveal rather narrow lines: full width at half maximum (FWHM) values of the strongest donor-bound exciton line are in the range from 6.0 to 1.8 meV and omega-2heta FWHM values are between 80 and 23 arcsec indicating good structural quality of the films. The ogema-rocking curves show a single peak for the thinnest films with a FWHM of 250 arcsec and multiple peaks with FWHM of about 250-350 arcsec in thicker films indicating the formation of several high-quality domains when increasing cither thickness or growth rate. Optical microscopy and AFM images reveal a domain type of morphology and also show an appearance of spiral hillocks in layers grown at growth rates exceeding a critical value. We interpret these results as dominating 2D multilayer growth at low growth rates, and competing 2D multilayer and spiral growth mechanisms at high growth rates.
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