| With the development of optoelectronic industry,transparent conductive oxide(TCO)thin films have been widely used as transparent electrode materials in electroluminescent devices,solar cells,transparent thin films transistors,and flat panel displays,and have become a research hot spot.Indium tin oxide(ITO)film,as a typical application case,has been widely used.Despite its high conductivity and optical properties,its expensive raw materials and less resources on Earth limit its future usage.At the same time,the continuous development of optoelectronic technology has put forward higher requirements for the performance of transparent electrodes in flexible display.The above issue has aroused people's research on ITO alternatives.Zinc oxide,as a wide band gap semiconducting metal oxide,is a promising material for TCO thin films due to being(i)non-toxic,abundant,and inexpensive;(ii)easily bent utilizing flexible substrates;and having(iii)tunable properties by doping to achieve high optical transmittance and low resistance.The conductivity of TCO films can be effectively improved by single-element dopants or alloying,and surely produce distortions in a periodic lattice,thus decreasing the crystallinity of TCO films.Binary-element co-dopants can compensate for the difference in the ion radius between the original and substituted ions if two kinds of ion substituents cause a counter-size effect,and probably improve the electronic mobility in Zn O films.Organic thin film transistors(OTFTs)have attracted much attention due to their wide applications in digital circuits,radio frequency identification tags and flat panel display driver circuits.Transparent organic thin film transistors have additional advantages in applications such as transparent electronic devices and flat panel displays.Transparent organic thin film transistors generally use organic materials as dielectric and active layer,but the dielectric properties of organic dielectric materials are poor.Alumina thin film is a potential high-k value gate dielectric layer material with high wear and corrosion resistance.Because of this,alumina thin films have important applications in optics,microelectronics,electronics,optical communication and catalysis.Therefore,the use of alumina film as gate insulating layer of transparent organic thin film transistors can be considered to enhance the dielectric properties of dielectric materials.Traditional preparation methods of alumina films are either complicated or expensive,such as magnetron sputtering and atomic layer deposition.Thermal oxidation of aluminum films requires only simple equipment and process,and the preparation process of alumina films has been very mature.Therefore,the method of obtaining transparent alumina dielectric films by thermal oxidation of aluminum films is of great significance.It also has certain application prospects.In order to prepare effective,controllable thickness,smooth and compact alumina thin films,the oxidation kinetics and regularity of nanocrystalline aluminum thin films were studied firstly.The relationship between thermal oxidation temperature,holding time and heating rate of aluminum thin films was determined,and the optimum technological conditions for preparing transparent alumina dielectric thin films were obtained.In this paper,two aspects of work have been done.One is to study the binary doping of Zn O by Eu F3 and Ho F3,respectively.The other is to prepare alumina thin films by thermal oxidation of aluminium thin films,and to study the oxidation kinetics of nanocrystalline aluminium thin films.The main research results are as follows:1.New N-type Eu and F co-doped Zn O transparent conductive films were deposited by ion source assisted electron beam evaporation.The effects of different doping concentration of Eu and F on the photoelectric properties of EFZO thin films were studied.The substitution of large radius Eu 3+ and small radius F-for Zn2+ and O2-,respectively,was realized.The lattice distortion was reduced.At the same time,F-plays an important role in filling oxygen vacancy defects.The optimized EFZO film has the average transmittance in the visible region of 82.9%,a resistivity of 5.7×10-4 ??cm,a carrier density of 1.86×1020 cm-3,and a mobility of 58.8 cm2/V?s.In addition,the actual performance of EFZO as a transparent electrode in OLED and QLED was evaluated.OLED based on the EFZO anode showed a maximum EQE of 20.9%,which is comparable to the state-of-the art results for devices based on the ITO anode.Inverted structural QLED based on the EFZO cathode were realized with a maximum current efficiency of 21.6 cd A-1 and a maximum luminance of 128000 cdm-2.Good EL performances in OLED and QLED demonstrate that EFZO electrodes exhibit efficient hole and electron injection abilities,and are a promising choice for low cost and high-performance TCO films.2.New N-type Ho F3 doped Zn O transparent conductive films were deposited by ion source assisted electron beam evaporation.The results show that the substitution of Ho for Zn and F for O can simultaneously increase the electron concentration and improve the mobility.The effects of different doping concentration of Eu and F on the photoelectric properties of EFZO thin films were studied.The doped thin films for Ho:Zn = 3.5 at% have a sheet resistance of 65?/sq and a resistivity of 9.37×10-4 ??cm,and Hall mobility and carrier concentration of 47.89 cm2/Vs and 1.39×1020 cm-3,respectively.The work-function value is around 5.069 e V,and the average transmittance in the visible region is more than 85%.Ho F3 doped Zn O thin films were annealed in air and vacuum respectively,and the heating temperature ranged from 100 to 500 ?.The effect of annealing temperature on the electrical and optical properties of Ho F3: Zn O thin films was analyzed.The thermal annealing in vacuum and air showed that the Ho F3 doped Zn O thin films had good thermal stability.To evaluate practical application value of Ho F3 doped Zn O films,all-inorganic Pe LEDs were fabricated by using the Ho F3 doped Zn O film as an anode.A maximum EQE value of 5.44% is achieved with a luminance of 34680 cd/m2.Ho F3 doped Zn O is a promising anode that facilitates carrier injection and practical application in display devices.3.Attempt was made to study the oxidation kinetics of the nanocrystalline Al ultrathin films.The influence of structure and composition evolution during thermal oxidation was observed.The reason for the change in the oxidation activation energy on increasing the oxidation temperature will be discussed.The activation energy for Al oxidation is 8.33±0.718 k J/mol at 400-500 ?,and it becomes-7.14±0.67 k J/mol at 500-600 ?.It was found that the oxidation kinetics of nanocrystalline Al films follows the logarithmic rule in air at 400-600 ?.The grain boundary and defect diffusion are believed to be the reason for the logarithmic oxidation rate rule.The activation energy is positive and low for the low temperature oxidation,but it becomes apparently negative at higher temperatures.The latter case comes from the decline of diffusion paths due to the formation of the ?-Al2O3 crystals.4.Aluminum thin films were prepared by vacuum thermal evaporation,and then transparent alumina thin films were prepared by annealing at different temperatures in air.The effects of annealing temperature on the morphology and structure of the films were investigated by means of AFM,XRD,SEM and EDS.The results show that all the surface roughness,thickness,crystal interface properties and dopants can affect the oxidation process.The results of optical and structural properties show that there exists a critical temperature of 500 ? over which a transparent film of ?-Al2O3 can be formed.The films were annealed at 500 ? for different time.After 9 hours of oxidation,the transmittance of the films was over 90%.The results show that the alumina films with high transmittance can be obtained by thermal oxidation of the aluminium films.These results show that transparent alumina thin films with controllable thickness and low surface roughness can prepared by thermal oxidation of aluminium thin films,which can be adopted to FETs devices as gate dielectric layer. |
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