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

Ku, C. S.; Peng, J. M.; Ke, W. C.; Huang, H. Y.; Tang, N. E.; Chen, W. K.; Chen, W. H.; Lee, M. C.
October 2004
Applied Physics Letters;10/4/2004, Vol. 85 Issue 14, p2818
Academic Journal
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 μm in diameter. In a previous study, the microphotoluminescence spectra showed an extra peak (Iv=350 nm) inside the V-defect besides the near-band-edge emission (Inbe=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 Iv band increased gradually from V-defect edges to its center, while Inbe 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 Iv band could be related to shallow acceptor levels, likely resulting from VGa defects.


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