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postgraduate thesis: Enhanced dielectric property of ZnO materials via acceptor-donor co-doping method

TitleEnhanced dielectric property of ZnO materials via acceptor-donor co-doping method
Authors
Advisors
Advisor(s):Ling, FCC
Issue Date2020
PublisherThe University of Hong Kong (Pokfulam, Hong Kong)
Citation
Huang, D. [黃棟]. (2020). Enhanced dielectric property of ZnO materials via acceptor-donor co-doping method. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR.
AbstractDielectrics has attracted wide attentions as its potential application in high-density energy storage system, electronic devices’ miniaturization such as field effect transistors. To enhance the dielectric constant and limit the dielectric loss are hardly achieved simultaneously. An acceptor-donor co-doping method is attempted in our work to design the defect complexes, where the electron in confined. In this way, the defect complex could contribute to the dielectric constant and the acceptor could compensate the free electrons. In our study, the (Lix, Aly)Zn1-x-yO ceramics are fabricated via solid state sintering process. When x=0.33%, y=0.67%, the dielectric property is optimized showing a relatively good frequency stability with =9862, tan=0.16 at 1 kHz. From the impedance spectroscopic analysis on (Li, Al) co-doped ZnO, the nonexistence of the resistive grain boundaries and semiconducting grain indicates that the traditional internal barrier capacitance mechanism is not the origin of the observed colossal dielectric constant phenomenon. Moreover, two relaxation P1 and P2 are identified by the Modulus spectroscopy. Further analyses including the annealing process and luminescence spectroscopy show that P1 relaxation process may originate from O-poor defect such as oxygen vacancies, and the O-poor defects mainly aggregate at grain boundaries and also the surface layer. For both the as grown and oxygen annealed samples, the frequency dependent AC conductivity obeys the correlated barrier hopping mechanism. Combined the correlated barrier hopping model and Kirkwood’s polarization theory, the dielectric constant and frequency dependent dielectric constant were simulated. It shows that both relaxation P1 and P2 totally contribute the dielectric constant of ~10016 and the dielectric loss of ~0.149 to the as-grown (Li, Al) co-doped ZnO ceramics while only P2 contributes the dielectric constant of ~2699 and the dielectric loss of ~0.05 to the O2-annealed one. Furthermore, it is found that, P2 is related with the LiZn-AlZn related defect dipoles. From the synchrotron hyperfine XPS and the Fourier transformed infra-red spectroscopy, it shows that the defect dipoles LiZn-AlZn still contributes the remained CDC phenomenon of the O2-annealed sample. The (Ga, Cu) co-doped ZnO thin films are fabricated by Pulse Laser Deposition method. When the dopant ratio of Ga and Cu are 0.5 wt% and 8 wt%, and P(O¬2) = 5 Pa, the dielectric property is optimized exhibiting a relatively good frequency stability, and the dielectric constant and loss are 204 and 0.27 at 1 kHz. In the dielectric spectroscopy, one Lorentzian peak is identified and attributed to the oscillator’s resonance. Simulation results shows that the resonance process is uncapable of producing the large dielectric constant. One relaxation process P1 is identified in the Modulus spectroscopy and related to the Correlated barrier hopping process. The simulation reveals that the relaxation P1 would contribute the dielectric constant of 204 and loss of 1.12, and the calculated ε(ω) exhibits relatively good frequency stability as same as the experimental data. The band offset between (Ga, Cu) co-doped ZnO and p-type Silicon is investigated using XPS measurement. It is found that a 1.47 nm layer of SiO2 exists at the interface, and the conduction and valence band offset are 0.17 and 2.42 eV respectively.
DegreeDoctor of Philosophy
SubjectZinc oxide - Electric properties
Dielectrics
Dept/ProgramPhysics
Persistent Identifierhttp://hdl.handle.net/10722/297556

 

DC FieldValueLanguage
dc.contributor.advisorLing, FCC-
dc.contributor.authorHuang, Dong-
dc.contributor.author黃棟-
dc.date.accessioned2021-03-21T11:38:05Z-
dc.date.available2021-03-21T11:38:05Z-
dc.date.issued2020-
dc.identifier.citationHuang, D. [黃棟]. (2020). Enhanced dielectric property of ZnO materials via acceptor-donor co-doping method. (Thesis). University of Hong Kong, Pokfulam, Hong Kong SAR.-
dc.identifier.urihttp://hdl.handle.net/10722/297556-
dc.description.abstractDielectrics has attracted wide attentions as its potential application in high-density energy storage system, electronic devices’ miniaturization such as field effect transistors. To enhance the dielectric constant and limit the dielectric loss are hardly achieved simultaneously. An acceptor-donor co-doping method is attempted in our work to design the defect complexes, where the electron in confined. In this way, the defect complex could contribute to the dielectric constant and the acceptor could compensate the free electrons. In our study, the (Lix, Aly)Zn1-x-yO ceramics are fabricated via solid state sintering process. When x=0.33%, y=0.67%, the dielectric property is optimized showing a relatively good frequency stability with =9862, tan=0.16 at 1 kHz. From the impedance spectroscopic analysis on (Li, Al) co-doped ZnO, the nonexistence of the resistive grain boundaries and semiconducting grain indicates that the traditional internal barrier capacitance mechanism is not the origin of the observed colossal dielectric constant phenomenon. Moreover, two relaxation P1 and P2 are identified by the Modulus spectroscopy. Further analyses including the annealing process and luminescence spectroscopy show that P1 relaxation process may originate from O-poor defect such as oxygen vacancies, and the O-poor defects mainly aggregate at grain boundaries and also the surface layer. For both the as grown and oxygen annealed samples, the frequency dependent AC conductivity obeys the correlated barrier hopping mechanism. Combined the correlated barrier hopping model and Kirkwood’s polarization theory, the dielectric constant and frequency dependent dielectric constant were simulated. It shows that both relaxation P1 and P2 totally contribute the dielectric constant of ~10016 and the dielectric loss of ~0.149 to the as-grown (Li, Al) co-doped ZnO ceramics while only P2 contributes the dielectric constant of ~2699 and the dielectric loss of ~0.05 to the O2-annealed one. Furthermore, it is found that, P2 is related with the LiZn-AlZn related defect dipoles. From the synchrotron hyperfine XPS and the Fourier transformed infra-red spectroscopy, it shows that the defect dipoles LiZn-AlZn still contributes the remained CDC phenomenon of the O2-annealed sample. The (Ga, Cu) co-doped ZnO thin films are fabricated by Pulse Laser Deposition method. When the dopant ratio of Ga and Cu are 0.5 wt% and 8 wt%, and P(O¬2) = 5 Pa, the dielectric property is optimized exhibiting a relatively good frequency stability, and the dielectric constant and loss are 204 and 0.27 at 1 kHz. In the dielectric spectroscopy, one Lorentzian peak is identified and attributed to the oscillator’s resonance. Simulation results shows that the resonance process is uncapable of producing the large dielectric constant. One relaxation process P1 is identified in the Modulus spectroscopy and related to the Correlated barrier hopping process. The simulation reveals that the relaxation P1 would contribute the dielectric constant of 204 and loss of 1.12, and the calculated ε(ω) exhibits relatively good frequency stability as same as the experimental data. The band offset between (Ga, Cu) co-doped ZnO and p-type Silicon is investigated using XPS measurement. It is found that a 1.47 nm layer of SiO2 exists at the interface, and the conduction and valence band offset are 0.17 and 2.42 eV respectively.-
dc.languageeng-
dc.publisherThe University of Hong Kong (Pokfulam, Hong Kong)-
dc.relation.ispartofHKU Theses Online (HKUTO)-
dc.rightsThe author retains all proprietary rights, (such as patent rights) and the right to use in future works.-
dc.rightsThis work is licensed under a Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International License.-
dc.subject.lcshZinc oxide - Electric properties-
dc.subject.lcshDielectrics-
dc.titleEnhanced dielectric property of ZnO materials via acceptor-donor co-doping method-
dc.typePG_Thesis-
dc.description.thesisnameDoctor of Philosophy-
dc.description.thesislevelDoctoral-
dc.description.thesisdisciplinePhysics-
dc.description.naturepublished_or_final_version-
dc.date.hkucongregation2020-
dc.identifier.mmsid991044351381903414-

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