Abstract: Thick GaN films were grown on GaN/sapphire template in a vertical HVPE reactor.Various material characterization techniques,including AFM,SEM,XRD,RBS/Channeling,CL,PL,and XPS,were used to characterize these GaN epitaxial films.It was found that stepped/terraced structures appeared on the film surface,which were indicative of a nearly step-flow mode of growth for the HVPE GaN despite the high growth rate.A few hexagonal pits appeared on the surface,which have strong light emission.After being etched in molten KOH,the wavy steps disappeared and hexagonal pits with {1010} facets appeared on the surface.An EPD of only 8e6cm-2 shows that the GaN film has few dislocations.Both XRD and RBS channeling indicate the high quality of the GaN thick films.Sharp band-edge emission with a full width at half maximum(FWHM)of 67meV was observed,while the yellow and infrared emissions were also found.These emissions are likely caused by native defects and C and O impurities.

Key words: GaN, HVPE, CL, RBS/channeling, yellow emission, infrared emission