Browsing by Author "Tang, NE"

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Near-field optical microscopy and scanning Kelvin microscopy studies of V-defects on AlGaN/GaN films
(2004-10-04)
Ku, CS
;
Peng, JM
;
Ke, WC
;
Huang, HY
;
Tang, NE
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.
Spatially-resolved photoluminescence studies of V-shaped pits on Al0.16Ga0.84N
(2004-02-15)
Huang, HY
;
Ku, CS
;
Ke, WC
;
Tang, NE
;
Peng, JM
We have studied optical properties of V-shaped pits on Al0.16Ga0.84N. The microphotoluminescence spectrum from the pit center shows a broader and stronger emission at 350 nm than the near-band-edge emission at 336 nm from nonpit regions. The results indicated specific defect levels associated with the V-shaped pits. Furthermore, after using atomic force microscopy to probe the surface electrical potential with a conductive tip, the pit's potential was similar to0.2 V lower than its surrounding region. A simplified energy diagram is tentatively proposed to interpret our observation. (C) 2004 American Institute of Physics.