Browsing by Author "Yang, S."

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Improvement of Crystalline and Photoluminescence of Atomic Layer Deposited m-Plane ZnO Epitaxial Films by Annealing Treatment
(2012-10-01)
Yang, S.
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Lin, B. H.
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Kuo, C. C.
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Hsu, H. C.
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Liu, W-R
Monocrystalline m-plane ZnO epitaxial films with flat surface morphology were grown on m-plane sapphire by using atomic layer deposition. X-ray diffraction and transmission electron microscopy measurements verify not only the in-plane epitaxial relationship of the as-grown films as (10 (1) over bar0)< 0001 >(ZnO)parallel to(10 (1) over bar0)<(1) over bar2 (1) over bar0 > Al2O3 but also the absence of domains with undesirable orientations, which are generally obtained in the m-plane ZnO films grown by other methods. Experimental results indicate that the basal plane stacking fault (BSF) is the dominant structural defects that contribute to the emission at 3.31 eV in m-plane ZnO films. Exactly how thermal annealing affects the structural and optical properties of ZnO epi-films was also investigated. Additionally, based on time-resolved photoluminescence at 5 K, the decay time of BSF related emission and near-band-edge (NBE) emission were determined. Results of this work further demonstrated that the decay time of NBE emission increases with a higher annealing temperature, accompanied by an improvement in crystal structure.
Photoluminescence associated with basal stacking faults in c-plane ZnO epitaxial film grown by atomic layer deposition
(2012-03-05)
Yang, S.
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Kuo, C. C.
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Liu, W. -R.
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Lin, B. H.
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Hsu, H. -C.
Basal plane stacking faults (BSFs) with density of similar to 1 x 10(6) cm(-1) are identified as the dominant defect in the annealed ZnO thin films grown on c-plane sapphire by atomic layer deposition. The dominant peak centered at 3.321 eV in low-temperature photoluminescence measurements is attributed to the emission from the BSFs. The emission mechanism is considered to be the confined indirect excitons in the region of quantum-well-like structure formed by the BSFs. The observed energy shift of 19 meV with respect to the BSF-bounded exciton at low temperature may be caused by the localization effect associated with the coupling between BSF quantum wells. (C) 2012 American Institute of Physics. [http://dx.doi. org/10.1063/1.3692730]
Recombination dynamics of a localized exciton bound at basal stacking faults within the m-(p)lane ZnO film
(2014-07-07)
Yang, S.
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Hsu, H. C.
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Liu, W-R.
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Lin, B. H.
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Kuo, C. C.
We investigated the carrier dynamics near basal stacking faults (BSFs) in m-plane ZnO epitaxial film. The behaviors of the type-II quantum wells related to the BSFs are verified through time-resolved and time-integrated photoluminescence. The decay time of the emission of BSFs is observed to have a higher power law value and longer decay time than the emission of the donor-bound excitons. The spectral-dependent decay times reveal a phenomenon of carriers migrating among band tail states, which are related to the spatial distribution of the type-II quantum wells formed by the BSFs. A high density of excited carriers leads to a band bending effect, which in turn causes a blue-shift of the emission peak of BSFs with a broadened distribution of band tail states. (C) 2014 AIP Publishing LLC.
Single Domain m-Plane ZnO Grown on m-Plane Sapphire by Radio Frequency Magnetron Sputtering
(2012-10-01)
Lin, B. H.
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Liu, W. -R
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Lin, C. Y.
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Hsu, S. T.
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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.
Structural Characteristics and Annealing Effect of ZnO Epitaxial Films Grown by Atomic Layer Deposition
(2009-12-01)
Yang, S.
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Lin, B. H.
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Liu, W. -R.
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Lin, J. -H.
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Chang, C. -S.
Structural characteristics of the ZnO epitaxial films grown on c-plane sapphire by the atomic layer deposition method were thoroughly studied. The in-plane axes of the e-plane oriented ZnO layers are predominantly aligned with that of the sapphire substrate, yielding the relationship of {10 (1) over bar0}(ZnO) parallel to {10 (1) over bar0}(Al2O3). The minor orientation with a 30 degrees in-plane twist configuration, that is, {10 (1) over bar0}(ZnO) parallel to {11 (2) over bar0}(Al2O3),which is more commonly observed in ZnO films grown by metal organic chemical vapor deposition, pulsed laser deposition, and other methods, only amounts to less than 3% and can be eliminated by thermal annealing. The structure of the ZnO, epi-films exhibits significantly improvement upon thermal annealing, and intrinsic types of basal plane stacking faults are the predominant Structural defects in the ZnO after thermal treatment. The effect of post growth thermal treatment is reported in this work.
The Growth of an Epitaxial ZnO Film on Si(111) with a Gd(2)O(3)(Ga(2)O(3)) Buffer Layer
(2011-07-01)
Lin, B. H.
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Liu, W. R.
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Yang, S.
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Kuo, C. C.
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Hsu, C. -H.
High-quality (0001)-oriented ZnO epitaxial films have been grown by pulsed laser deposition on Si(111) buffered with a nanometer-thick Gd(2)O(3)(Ga(2)O(3)), GGO, layer. The structural characteristics of the ZnO epi-layers were studied by X-ray diffraction and transmission electron microscopy (TEM). The in-plane epitaxial relationship between the wurtzite ZnO, cubic GGO, and cubic Si follows {10 (1) over bar0}(ZNO)parallel to{4 (22) over bar}(Gd2O3)parallel to{(4) over bar 22}(Si) and the ZnO/GGO interface can be described by the domain matching epitaxy. TEM contrast analysis reveals that the major defect structures in the ZnO films are edge-type threading dislocations and intrinsic basal plane stacking faults. All the ZnO epi-films studied are under a tensile biaxial strain, but no cracks were found. Temperature-dependent photoluminescence results show the excellent optical properties of the obtained ZnO layers, and the origins of the spectral features are discussed.
The Growth of an Epitaxial ZnO Film on Si(111) with a Gd2O3(Ga2O3) Buffer Layer
(2011-07-01)
Lin, B. H.
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Liu, W. R.
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Yang, S.
;
Kuo, C. C.
;
Hsu, C. -H.
High-quality (0001)-oriented ZnO epitaxial films have been grown by pulsed laser deposition on Si(111) buffered with a nanometer-thick Gd2O3(Ga2O3), GGO, layer. The structural characteristics of the ZnO epi-layers were studied by X-ray diffraction and transmission electron microscopy (TEM). The in-plane epitaxial relationship between the wurtzite ZnO, cubic GGO, and cubic Si follows {10 (1) over bar0}(ZNO)parallel to{4 (22) over bar}(Gd2O3)parallel to{(4) over bar 22}(Si) and the ZnO/GGO interface can be described by the domain matching epitaxy. TEM contrast analysis reveals that the major defect structures in the ZnO films are edge-type threading dislocations and intrinsic basal plane stacking faults. All the ZnO epi-films studied are under a tensile biaxial strain, but no cracks were found. Temperature-dependent photoluminescence results show the excellent optical properties of the obtained ZnO layers, and the origins of the spectral features are discussed.
The influence of dislocations on optical and electrical properties of epitaxial ZnO on Si (111) using a gamma-Al2O3 buffer layer
(2012)
Liu, W. -R.
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Lin, B. H.
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Yang, S.
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Kuo, C. C.
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Li, Y. -H.
The structural, optical and electrical properties of the c-plane ZnO epitaxial films grown by pulsed laser deposition on a Si(111) substrate buffered with a thin layer of gamma-Al2O3 were investigated by X-ray diffraction, transmission electron microscopy, photoluminescence (PL) and Hall measurements. Detailed structural investigation showed that the dominant structural defects in the ZnO films are threading dislocations (TDs). Experimental results manifest the edge-and screw-type of TDs influence the optical and electric properties differently; the intensity ratio between the PL yellow-green band to near band edge emission and the carrier concentration are affected mainly by the edge TD, and the FWHM of the near band edge emission is dominantly influenced by the screw TD.
ZnO nanopowders fabricated by dc thermal plasma synthesis
(2006-09-25)
Ko, T. S.
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Yang, S.
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Hsu, H. C.
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Chu, C. P.
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Lin, H. F.
Ultrafine ZnO nanopowders were successfully synthesized by the de thermal plasma process with a high production rate of 1.2 kg/h. The combination of plasma was found to affect the nanoparticles morphology. Both X-ray diffraction and Raman spectrum analysis confirmed a high quality wurtzite structure of the ZnO nanopowders. Photoluminescence study exhibited strong ultraviolet emission corresponding to the near band edge emission in the ZnO nanopowders. Random laser action observed in the ZnO nanostructures by optical pumping demonstrated high optical and crystal quality of the ZnO nanopowders fabricated by the dc thermal plasma synthesis. (c) 2006 Elsevier B.V. All rights reserved.