A near-field scanning optical microscopy study of the photoluminescence from GaN films

We have achieved spatially resolved photoluminescence from GaN films using a near-field scanning optical microscope (NSOM). GaN films grown by hydride vapor phase epitaxy (HVPE) and metal-organic vapor phase epitaxy (MOVPE) on sapphire substrates have been studied. We have performed spatial scans of topography, band edge, and yellow luminescence signals. Atomic force microscopy measurements were also made and compared with the NSOM topography. We have found spatial variations in photoluminescence characteristics at the submicron scale for both HVPE and MOVPE GaN. The observed enhancement of yellow luminescence at multiatomic step edges on the HVPE GaN surface suggests that the yellow luminescence is associated with chemical impurities incorporated during the growth of GaN films.