Development and application of a near-field scanning optical microscope in the studies of compound semiconductor materials

A Near-Field Scanning Optical Microscope (NSOM) was designed and optimized to perform photoluminescence (PL) measurements with sub-micron scale spatial resolution. We have studied the uniformity of GaAs surface passivation by NSOM in a semi-quantitative fashion. The variation of band edge PL intensity is related to the change of surface state density. The high spatial resolution PL measurements from GaN films have been performed. The defect-related yellow luminescence is found to be enhanced at step edges on GaN grown by halide vapor phase epitaxy. The origin of yellow luminescence is suggested to be chemical impurities incorporated in the material. A finite element method based numerical model has been developed and used to analyze the carrier transport. The lateral distribution of photo-generated carriers is shown to be narrowed due to the presence of a large surface recombination velocity. As a result, high spatial resolution can be achieved for NSOM PL measurements.