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Synthesis And Photoluminescence Properties Of Ga-N Codoped ZnO Nanowires

Posted on:2018-08-24Degree:MasterType:Thesis
Country:ChinaCandidate:M LouFull Text:PDF
GTID:2321330512497883Subject:Microelectronics and Solid State Electronics
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With the rapid development of global economy,science and technology,more and more devices transform to miniaturization and integration,and promote the development of nanostructures and nanomaterials.In the last few decades,study of low-dimensional nanomaterials has become a leading in nanoscience and nanotechnology.With the reduction in size,novel electrical,mechanical,chemical and optical properties are introduced,which are largely believed to be the result of surface and quantum confinement effects.As a new type of light source,white light-emitting diodes?W-LEDs?are mentioned as the fourth generation lighting source.Reasonable efficiency,high stability,and easy and economical fabrication methods makes W-LEDs devices a good choice for mass production.Due to the wide applications of white LEDs,different methods and different studies for fabrication of these devices are discussed.At present,the most promising realization of white-LEDs is GaN-based blue LED pumping a complimentary yellow phosphor,and have been successfully commercialized.However,the preparation process of GaN is complex and expensive,and it is difficult to obtain GaN nanowires by a direct growth until now.ZnO,with a large direct band gap of 3.37 eV,is a promising candidate for LED because of characteristic features such as a large exciton binding energy of 60 meV,and the realization of band gap engineering to create barrier layers and quantum wells with little lattice mismatch.Zn O crystallizes in the hexagonal wurtzite structure,the same as GaN,but,in contrast,large ZnO single crystal can be fabricated.Furthermore,ZnO is inexpensive,chemically stable,easy to prepare and etch,and nontoxic.ZnO-based LED show great promise for the future.In the photoluminescence?PL?spectra of ZnO,typically there are emission bands in the ultraviolet?UV?and visible?green,yellow and blue?regions.The UV emission is usually considered as the characteristic emission of ZnO,and attributed to the band-edge transition or the exciton combination,not in blue region.However,it is hard to directly tune band gap on ZnO for blue emission.Band gap engineering is the process of controlling or altering the band gap of ZnO by controlling the composition of certain semiconductor alloys.Ga doped n-ZnO/p-GaN photoluminescence?PL?spectra continuously shift from ultraviolet to visible region,but high-level Ga doped related high defect recombination resulted the broad and low efficiency emission of LED chips.Research shows that GaN/ZnO alloys can achieve 2.7 eV?460 nm?band gap.In addition,ZnO nanowires,being a result of self-assembling growth,has a much lower defect density than bulk ZnO materials,so,it could be of high light emission efficiency.Nanowires can also act as direct waveguide and favor light extraction without the use of lenses and reflectors.Here we report the use of chemical vapor deposition to grow Ga-N codoped ZnO nanowires via the vapor-liquid-solid?VLS?mechanism.Nanowires were grown on Au-coated sapphire substrate.Research works and main conclusion of this paper are described as follows:1.Ga doped ZnO nanowires were prepared by three-step,solid-state diffusion technique.Compared Zn O nanowires were carried out by chemical vapor deposition route,different weight ratios of Ga2O3/ZnO were doping sources.It is difficult to realize high-level doping content.In this paper,we evaporation Ga metal on the ZnO nanowires by thermal evaporation.So we can control the Ga doping content by controlling the thickness of the Ga coating.First,ZnO nanowires were grown on Au-coated c-sapphire substrate by chemical vapor deposition,then Ga metal were evaporated on nanowires,and last the Ga-coated samples were anneaLEDs to form thermally stable.The results show that the average diameter increased with the increased of doping contents,XPS measurements show that the Ga 2p,Zn 2p peaks are shifted and the VO concentration changed by changing the doping contents.The optoelectronics properties of the Ga-N codoped ZnO nanowires were also evaluated by PL spectra.The results show that the near-band-edge emission peaks show a significant red shift,and the defect-related emission increased.2.In this paper,the Ga-N codoped ZnO nanowires were synthesized via catalyzed epitaxial growth on?0001?-sapphire,by using Ga2O3 and NO as doping sources.Compared with three-step,solid-state diffusion technique,Ga-N codoped ZnO nanowires by chemical vapor deposition route can achieve the upgrade of efficiency.With the increase of doping contents,the morphology of the doped ZnO nanowires are transformed from hexagonal structure to cone type,and the average length of ZnO nanowires decreases from 2?m to 1?m at the same time.XPS measurements show that the Ga 2p,Zn 2p and N 1s peaks are shifted to lower binding energy after doping in ZnO nanowires.The optoelectronics properties of the Ga-N codoped ZnO nanowires were also evaluated by PL spectra.The results show that the near-band edge UV emission peak and green emission peak are detected.In addition,the PL peaks positions are shifted and the intensity rate of UV/Vis peaks is varied by changing the doping contents.
Keywords/Search Tags:Blue LED, Band gap engineering, Ga-N codoped ZnO nanowires, chemical vapor deposition, thermal evaporation, photoluminescence(PL) spectra
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