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postgraduate thesis: Defect emission of ZnO and its related origins

TitleDefect emission of ZnO and its related origins
Authors
Issue Date2014
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Wang, Z. [王子蘭]. (2014). Defect emission of ZnO and its related origins. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b5481893
AbstractZinc oxide (ZnO) is a promising material for ultra-violet optoelectronics applications due to its direct band gap and large exciton binding energy. Defect in semiconductor plays an important role in determining the optical and electrical properties. It is thus crucial to understand the defects‟ performance for realizing the device fabrication. Green luminescence (GL) having the peak at 2.4-2.5 eV is a defect related emission band commonly found in the luminescence spectra of many of the ZnO materials. Despite of the effort devoted for several decades, its origin and emission mechanism remain controversial. In this thesis, the origin of the GL emitted from the ZnO films grown by pulsed laser deposition (PLD) is studied using a comprehensive spectroscopic approach, including the Hall effect measurement, photoluminescence (PL), Raman spectroscopy, positron annihilation spectroscopy (PAS), and secondary ion mass spectroscopy (SIMS). ZnO thin films are grown by PLD method with the growth parameters (namely the substrate temperature and oxygen pressure during the growth) systemically varied. Annealing studies in argon atmosphere reveal the correlation between the free electron concentration and the hydrogen concentration in the samples. Two oxygen deficient defect related Raman modes are also identified and they anneal out after annealing at high temperature. We have investigated the introduction the GL systematically grown by different growth parameters, undergone different post-growth annealing treatment, and different methods of growth. Two kinds of GL’s are identified. The first kind of GLs has peak at 2.47 eV without the fine structure, and the other has the peak at 2.45 eV having the fine structure of separation of 0.07 eV. The GL with the fine structure is originated from the surficial region of the ZnO film. The GL without the fine structure is introduced after the annealing 900℃ irrespective of the initial growth conditions. PAS results show a strong correlation between the thermal introductions of a kind of Zn-vacancy and the GL without the fine structure. Moreover, a donor-acceptor-pair (DAP) emission is induced in the low temperature PL spectrum after the same annealing temperature of 900℃. The GL and the DAP emissions are thus associated with the involvement of the VZn. Furthermore by comparing the photon energies of the GL and DAP with the previous first principle calculated results, the GL is ascribed to the conduction band to the (-/2-) acceptor level of VZn, and the DAP involves the (0/-) acceptor level of VZn The presence of the conduction band to the (0/-) level transition is compatible with the results of the photoluminescence excitation (PLE) study.
DegreeDoctor of Philosophy
SubjectZinc oxide - Defects
Dept/ProgramPhysics
Persistent Identifierhttp://hdl.handle.net/10722/211111

 

DC FieldValueLanguage
dc.contributor.authorWang, Zilan-
dc.contributor.author王子蘭-
dc.date.accessioned2015-07-07T23:10:40Z-
dc.date.available2015-07-07T23:10:40Z-
dc.date.issued2014-
dc.identifier.citationWang, Z. [王子蘭]. (2014). Defect emission of ZnO and its related origins. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR. Retrieved from http://dx.doi.org/10.5353/th_b5481893-
dc.identifier.urihttp://hdl.handle.net/10722/211111-
dc.description.abstractZinc oxide (ZnO) is a promising material for ultra-violet optoelectronics applications due to its direct band gap and large exciton binding energy. Defect in semiconductor plays an important role in determining the optical and electrical properties. It is thus crucial to understand the defects‟ performance for realizing the device fabrication. Green luminescence (GL) having the peak at 2.4-2.5 eV is a defect related emission band commonly found in the luminescence spectra of many of the ZnO materials. Despite of the effort devoted for several decades, its origin and emission mechanism remain controversial. In this thesis, the origin of the GL emitted from the ZnO films grown by pulsed laser deposition (PLD) is studied using a comprehensive spectroscopic approach, including the Hall effect measurement, photoluminescence (PL), Raman spectroscopy, positron annihilation spectroscopy (PAS), and secondary ion mass spectroscopy (SIMS). ZnO thin films are grown by PLD method with the growth parameters (namely the substrate temperature and oxygen pressure during the growth) systemically varied. Annealing studies in argon atmosphere reveal the correlation between the free electron concentration and the hydrogen concentration in the samples. Two oxygen deficient defect related Raman modes are also identified and they anneal out after annealing at high temperature. We have investigated the introduction the GL systematically grown by different growth parameters, undergone different post-growth annealing treatment, and different methods of growth. Two kinds of GL’s are identified. The first kind of GLs has peak at 2.47 eV without the fine structure, and the other has the peak at 2.45 eV having the fine structure of separation of 0.07 eV. The GL with the fine structure is originated from the surficial region of the ZnO film. The GL without the fine structure is introduced after the annealing 900℃ irrespective of the initial growth conditions. PAS results show a strong correlation between the thermal introductions of a kind of Zn-vacancy and the GL without the fine structure. Moreover, a donor-acceptor-pair (DAP) emission is induced in the low temperature PL spectrum after the same annealing temperature of 900℃. The GL and the DAP emissions are thus associated with the involvement of the VZn. Furthermore by comparing the photon energies of the GL and DAP with the previous first principle calculated results, the GL is ascribed to the conduction band to the (-/2-) acceptor level of VZn, and the DAP involves the (0/-) acceptor level of VZn The presence of the conduction band to the (0/-) level transition is compatible with the results of the photoluminescence excitation (PLE) study.-
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsCreative Commons: Attribution 3.0 Hong Kong License-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.subject.lcshZinc oxide - Defects-
dc.titleDefect emission of ZnO and its related origins-
dc.typePG_Thesis-
dc.identifier.hkulb5481893-
dc.description.thesisnameDoctor of Philosophy-
dc.description.thesislevelDoctoral-
dc.description.thesisdisciplinePhysics-
dc.description.naturepublished_or_final_version-

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