Growth and characterization of GaN films on (0001) sapphire substrates by alternate supply of trimethylgallium and NH3

GaN films were grown on (0001) sapphire substrates in a temperature range of 500∼950°C by exposing the substrates to trimethylgallium (TMG) and NH3 one at a time. High quality GaN films were achieved at 800∼900°C with a thin GaN buffer layer predeposited at 500°C. The linewidth of the (0004) double-crystal rocking curve X-ray diffraction (DCXRD) of a 2.0 μm thick GaN film is about 250∼500 arcsec. Increment in growth temperature over a temperature range of 800∼900°C is helpful to suppress the intensity of yellow luminescence and to enhance the luminescence intensity of the near band-to-band emission. Typically, the room temperature photoluminescence intensity ratio of the near band edge emission to the yellow luminescence for an as-grown high quality GaN film is more than one order of magnitude. The best GaN films with superior optical behavior were achieved at ∼900°C with a V/III ratio of 5000. Photoluminescence measurements of these GaN films at 9 K show strong and sharp near band-to-band emission with almost no yellow luminescence.