Browsing by Author "Chien, F. S. -S."

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Effect of Threading Dislocations on Local Contacts in Epitaxial ZnO Films
(2010)
Lin, C. Y.
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Liu, W. -R.
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Chang, C. S.
;
Hsu, C. -H.
;
Hsieh, W. F.
Local conductance of a ZnO epifilm with a columnar-grain structure was studied by conductive-mode atomic force microscopy. The probe-ZnO junction at the grain boundary with high density edge threading dislocations (TDs) behaves as a Schottky contact while the junction at the epitaxial core behaves as an ohmic contact, resulting in the nonuniformity of conductance throughout the film. The calculated Schottky barrier is 0.4 +/- 0.025 eV. The point defects of doubly charged Zn vacancies accumulated at the edge TDs induce local band bending of ZnO, thus contributing to the Schottky nature at the grain boundary.
Influence of the threading dislocations on the electrical properties in epitaxial ZnO thin films
(2006-12-29)
Liu, W. -R.
;
Hsieh, W. F.
;
Hsu, C. -H.
;
Liang, K. S.
;
Chien, F. S. -S.
The structural and electrical properties of epitaxial ZnO films grown by pulsed-laser deposition on sapphire (0001) were investigated by high-resolution X-ray diffraction (XRD), atomic force microscopy (AFM), scanning capacitance microscopy (SCM), conductive atomic force microscopy (C-AFM), and transmission electron microscopy (TEM). The results of XRD and AFM revealed that the ZnO films have a columnar-grain structure consisting of epitaxial cores surrounded by annular boundaries. The core and boundary regions exhibited significantly different capacitive responses and field emission current. The results of TEM indicated that the annular boundaries have high-density edge threading dislocations. The shift of flatband voltage and the raise of potential barrier at the boundaries observed by SCM and C-AFM were attributed to the interface trap densities caused by the existence of high-density edge threading dislocations. (c) 2006 Elsevier B.V. All rights reserved.
Polar orientation induced by local photo-assisted poling in azo copolymer films
(2010-04-01)
Chien, F. S. -S.
;
Lin, C. Y.
;
Huang, C. R.
;
Chang, C. S.
;
Hsu, C. C.
Polar orientation created by local photo-assisted poling (PAP) in copolymer films containing disperse red 1 was investigated by scanning probe microscopy. PAP was performed by a proximal biased probe, and the polar orientation was semiquantitatively measured by electrostatic force microscopy. The polar orientation behaves as a biexponential function of the period of PAP, which is dominated by fast angular hole burning and slow angular redistribution (AR). The characteristic time of AR decreases linearly with the poling bias. An expression has been developed to interpret the evolution of the Lorentzian-like shape of the poled spots. A poled spot with 150 nm FWHM was demonstrated. (C) 2010 Optical Society of America
Polar orientation induced by local photo-assisted poling in azo copolymer films
(2010-04-01)
Chien, F. S. -S.
;
Lin, C. Y.
;
Huang, C. R.
;
Chang, C. S.
;
Hsu, C. C.
Polar orientation created by local photo-assisted poling (PAP) in copolymer films containing disperse red 1 was investigated by scanning probe microscopy. PAP was performed by a proximal biased probe, and the polar orientation was semiquantitatively measured by electrostatic force microscopy. The polar orientation behaves as a biexponential function of the period of PAP, which is dominated by fast angular hole burning and slow angular redistribution (AR). The characteristic time of AR decreases linearly with the poling bias. An expression has been developed to interpret the evolution of the Lorentzian-like shape of the poled spots. A poled spot with 150 nm FWHM was demonstrated. (C) 2010 Optical Society of America
Single Domain m-Plane ZnO Grown on m-Plane Sapphire by Radio Frequency Magnetron Sputtering
(2012-10-01)
Lin, B. H.
;
Liu, W. -R
;
Lin, C. Y.
;
Hsu, S. T.
;
Yang, S.
High-quality m-plane orientated ZnO films have been successfully grown on m-plane sapphire by using radio frequency magnetron sputtering deposition. The introduction of a nanometer-thick, low-temperature-grown ZnO buffer layer effectively eliminates inclusions of other undesirable orientations. The structure characteristics of the ZnO epi-layers were thoroughly studied by synchrotron X-ray scattering and transmission electron microscopy (TEM). The in-plane epitaxial relationship between ZnO and sapphire follows (0002)(ZnO) parallel to (11 (2) over bar0)(sapphire) and (11 (2) over bar0)(ZnO) parallel to (0006)(sapphire) and the ZnO/sapphire interface structure can be described by the domain matching epitaxy along the [11 (2) over bar0](ZnO) direction. The vibrational properties of the films were investigated by polarization dependent micro-Raman spectroscopy. Both XRD and micro-Raman results reveal that the obtained m-ZnO layers are tinder an anisotropic biaxial strain but still retains a hexagonal lattice.
Threading dislocations in domain-matching epitaxial films of ZnO
(2007-10-01)
Liu, W.-R.
;
Hsieh, W. F.
;
Hsu, C.-H.
;
Liang, Keng S.
;
Chien, F. S. -S.
The structures of high-quality ZnO epitaxial films grown by pulsed-laser deposition on sapphire ( 0001) without an oxygen gas flow were investigated by X-ray diffraction and transmission electron microscopy. The great disparity of X-ray diffraction line widths between the normal and in-plane reflections reveals the specific threading dislocation geometry of ZnO. Most threading dislocations are pure edge dislocations. From a combination of scattering and microscopic results, it is found that threading dislocations are not uniformly distributed in the ZnO films, but the films consist of columnar epitaxial cores surrounded by annular regions of edge threading dislocations in large density. The local surface morphology and capacitance signal obtained from atomic force and scanning capacitance microscopes indicate that the aggregation of threading dislocations leads to high interface traps at the annular regions.