Browsing by Author "Yang, Song"

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Correlation between photoluminescence and varied growth pressure of well-aligned ZnO nanorods on fused silica substrate
(2007-11-01)
Yang, Song
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Hsu, Hsu-Cheng
;
Liu, Wei-Ren
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Cheng, Hsin-Min
;
Hsieh, Wen-Feng
Well-aligned ZnO nanorods with variable diameters were fabricated on fused silica substrates by the simple physical vapor deposition method with and without pre-deposited NiO particles. The diameter control of ZnO nanorods on the fused silica substrates was achieved by varying the growth pressure. The room-temperature photoluminescence spectra of the ZnO nanorods exhibit strong exciton emission at 3.25 eV that reveals good crystal quality. The exciton emission peak shifts toward 3.22 eV for the samples made at the larger growth pressure that is attributed to the influence of the electron-acceptor-level transition. The ZnO nanorods were examined by high resolution transmission electron microscopy and X-ray diffraction to show single crystal quality and preferentially c-axis alignment. Furthermore, we used scanning electron microscope to verify not only the size but also the growth mechanisms of ZnO nanorods. The results show a ZnO buffer layer formed between the flat top-facet nanorods and the substrate. In comparison with the samples without pre-deposited NiO particles on the substrate, the pre-deposited NiO particles act as nucleation centers for Zn vapor during the deposition process that improves the quality of the buffer layer. (C) 2007 Elsevier B.V. All rights reserved.
Surface-bound-exciton emission associated with domain interfaces in m-plane ZnO films
(1970-01-01)
Kuo, C. C.
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Lin, B. H.
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Yang, Song
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Liu, W. R.
;
Hsieh, W. F.
"Small amount of (10 (1) over bar3)(ZnO) domains were found in the m-plane ZnO films grown on m-sapphire by pulsed laser deposition, which provide strain relaxation of the m-ZnO matrix behaving as a low strain layer. Through carefully correlating low-temperature polarized photoluminescence spectra with the x-ray diffraction peak intensity ratio of (10 (1) over bar3)(ZnO)/(10 (1) over bar0)(ZnO) of the samples grown at different temperature and after thermal treatment, we found that the broad-band emission around 3.17 eV may result from the interface defects trapped excitons at the boundaries between the (10 (1) over bar3)(ZnO) domains and the m-ZnO matrix. The more (10 (1) over bar3)(ZnO) domains in the m-ZnO layer cause the more surface boundary that makes the stronger surface-bound-exciton emission. And the a-axes of both the (10 (1) over bar3)(ZnO) domains and the m-ZnO matrix are aligned with the c-axis of the sapphire (alpha-Al2O3) substrate. The c-axis of the (10 (1) over bar3)(ZnO) domains rotates by about +/- 59 degrees against the common a-axis of the m-ZnO. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4732140]"
The effect of thermal annealing on the optical and electrical properties of ZnO epitaxial films grown on n-GaAs (001)
(2015-01-01)
Liu, Wei-Rein
;
Lin, Bi-Hsuan
;
Lin, Chi-Yuan
;
Yang, Song
;
Kuo, Chin-Chia
Wurtzite ZnO epitaxial layers grown on n-type GaAs (001) by pulsed laser deposition (PLD) exhibited n-type conductivity. Post-growth annealing leads the conversion of carrier type from electron to hole, as revealed by Hall effect measurements, although only moderate structural improvement was observed. The carrier type conversion is attributed to thermally activated arsenic diffusion from the substrate, confirmed by secondary ion mass spectrometry and photoluminescence. The surface electrical properties of both the as-deposited n-type and annealed p-type ZnO epitaxial layers were thoroughly characterized by Kelvin force microscopy (KFM) and electrostatic force microscopy (EFM). The results indicated the existence of a high density of surface states close to the ZnO midgap with a density of a few 10(14) cm(-2) eV(-1). The Fermi levels (E-F) of n- and p-type ZnO epitaxial layers were found to be 1.06 eV below the conduction-band minimum (CBM) and 1.612-1.769 eV above the valence-band maximum (VBM), respectively. The small EF difference between the n- and p-type ZnO epitaxial layers implies Fermi level pinning at the surface of both n-and p-type ZnO epitaxial layers.