A tapping-mode scanning near-field optical microscope was developed in order to measure near-field photoluminescence with nm spatial resolution by using an ultra-violet laser. The defect distribution in a Si-doped GaN film was measured. The results were compared with those measured using high spatial resolution cathodoluminescence spectroscopy. Some dark spots with an average period of 100 to 300nm were observed in the image of the peak intensity of near-field photoluminescence at about 362nm, measured with a pyramidal cantilever, and in a plan-view cathodoluminescence image at the same wavelength. The near-field photoluminescence image agreed well with the plan-view cathodoluminescence image. The threading dislocations in GaN films were found to act as non-radiative recombination centers not only for band-edge emission but also for yellow luminescence around 580nm. It was also found that the free carrier concentration decreased near to the threading dislocations. The high spatial resolution photoluminescence which was developed had a spatial resolution of about 100nm. The high spatial resolution  photoluminescence could potentially be applied to the estimation, at the nm scale, of defects in semiconductor films without requiring a vacuum environment.

Defect Characterization of Si-Doped GaN Films by a Scanning Near-Field Optical Microscope-Induced Photoluminescence. M.Yoshikawa, R.Sugie, M.Murakami, T.Matsunobe, K.Matsuda, H.Ishida: Applied Physics Letters , 2006, 88[16], 161905 (3pp)