A tapping-mode scanning near-field optical microscope was developed in order to measure near-field photoluminescence with nanometer spatial resolution using an ultraviolet laser, and the defect distribution of a Si-doped GaN film was measured. The obtained result was compared with one measured by high spatial resolution cathodoluminescence spectroscopy. Some dark spots with an average period of 100–300nm 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 centres not only for band-edge emission but also for yellow luminescence around 580nm. Furthermore, it was found that free carrier concentration decreased near the threading dislocations. The near-field photoluminescence which was developed had a spatial resolution of at least 100nm. The near-field photoluminescence could potentially be applied to the estimation at a nanometer 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)