Near-field optical microscopy and scanning Kelvin microscopy studies of V-defects on AlGaN/GaN films

Abstract

AlxGa1-xN thin film was grown on undoped GaN/sapphire (0001) substrate by metalorganic chemical vapor deposition. V-defects were directly observed by atomic force microscopy (AFM) with various size of 0.5-2 mum in diameter. In a previous study, the microphotoluminescence spectra showed an extra peak (I-v=350 nm) inside the V-defect besides the near-band-edge emission (I-nbe=335 nm). To achieve better spatial resolution, we used near-field scanning optical microscopy (NSOM) and scanning Kelvin-force microscopy (SKM) to probe the V-defect in detail. The NSOM spectra showed that the intensity of the I-v band increased gradually from V-defect edges to its center, while I-nbe remained unchanged. Besides, the SKM measurements revealed that the Fermi level decreased from the flat region to V-defect center by about 0.2 eV. These results suggest that the I-v band could be related to shallow acceptor levels, likely resulting from V-Ga defects. (C) 2004 American Institute of Physics.