| Transparent conductive films are such photolectric materials that combine optical transparency and good electrical conductivity.They are widely used in photoelectric devices such as Flat-panel displays,solar cells,light emitting diodes?LEDs?,gas sensor,energy saving glass.The indium tin oxide film?ITO?film is most widely applied at present,but the practical application of ITO thin films has been restricted because main component of the ITO thin film is a rare expensive and toxic element Indium.ZnO is a ?-? semiconductor material with wide band-gap and hexagonal wurtzite structure.Transparent conductive oxide thin film based on ZnO has become a hot issue and preferred materials instead of ITO films,because of their comparable optical and electrical properties?high optical transparency in the visible range,low electrical resistivity? to ITO films,what's more,they are moer and more attractive for their lower price and higher thermal and chemical stability under the exposure to hydrogen plasma than ITO.In this paper,High quality of the transparent conductive oxide thin films based on ZnO were prepared by radio frequency?RF? magnetron sputtering with zinc oxide ceramics target on glass substrate.The films obtained were characterized and analyzed by X-Ray Diffraction?XRD?,Scanning Electron Microscope?SEM?,X-ray photoelectron spectroscopy?XPS?and UV-Visible-Infrared Spectrophotometer.The conduction mechanism of the films has been analyzed and the electrical properties had been investigated by Van der Pauw method.It was changed such as substrate temperature,oxygen argon ratio and process conditions,power,air pressure in the process of preparation.We study the influence of various parameters for the thin film photovoltaic performance and it is concluded that the best process parameters through orthogonal experiments.The optimum conditions of preparation of AZO films by RF magnetron sputtering are using the doping concentration of 2%,ratio of oxygen and argon 0:30,substrate temperature of room temperature,working pressure of 3Pa,target substrate distance of 55mm,and power of 120W. Under the condition of preparation the AZO thin films gained the transmittance as high as 80%,and the resistivity down to 1×10-3 ?·cm.Based on the optimization of process parameters,we pay attention to the annealing process,film thickness,and AgNW cover,to study the evolution of AZO microstructure and photoelectric properties from the view point of surface and interface.We also carry out the aging experiment of films exposed in high temperature and high humidity to explore the mechanism of degradation of the electrical properties of thin film annealing.The result shows that the AZO thin films annealed in vacuum and show lower resistivity than others,in especial the carrier mobility increaed significantly after annealing in vacuum,combined with O1s electronic state analysis,we believed the increasing mobility mainly result from the vacuum annealing environment in AZO grain boundaries.The adsorption of O diffused to the outside world from the grain boundary,the defect concentration decreased,the scattering effect on the carrier weakened.When the AZO film is thicker,the degree of crystallization and orientation are better,far away from the interface with grain gradually grew up,forming a large crystal grain,the structure is more compact.When the film thickness reaches 2.5 AZO?m,carrier concentration and mobility are obviously increased,the resistivity can reach 8.24 × 10-4?·cm.But AZO film thickness is too thick,the optical transmittance will decline.Then we study the characteristics of stable environment in AZO films.The indoor environment after 24 days of AZO thin film resistance increased by 11.1%,while the resistance film of high temperature and high humidity environment.The test results show that the decline in the electrical properties of 95.5%.The electrical property degradation is not result from the carrier concentration,but the reduced carrier mobility.Combined with the results of XPS depth elements can also be found to internal diffusion O obviously,but also contains O2,H2O,CO2 and other strong covalent products.Finally we try on the AZO film coated with a layer of AgNW and vacuum annealing treatment,surface resistance of composite films from 24?/? reduced to 9.8 ?/?,environmental stability has been greatly improved.Because the AgNW forming conductive channel network structure on the surface of AZO film,the weakening of the scattering effect on the carrier of grain boundary film surface,so as to overcome the negative effects of hygrothermal environment through the AZO thin film grain boundary brings.Changing the doping concentration and doping element can be introduced to investigate the mechanism and the main influence factors of electric conductivity.With the increase of Al doping concentration,the conductivity of ZnO was increased at first and then decreased,when the doping concentration was 2%,the best performance of the conductive film,low resistivity and the carrier concentration is the main reason for the high with relatively high effective doping rate.Through the mixed atmosphere sputtering of Ar and H2,Al co-doped ZnO films with H passivation can effectively improve the carrier concentration,the electron concentration of thin film is 6.416×1020 cm-3,so the resistivity is further reduced to 6.49 ×10-4 ?·cm,the optical band gap of the films reached 3.78 eV.The results show that H passivation can not only influence the structure of AZO films,the conductivity will play the role of the donor film is improved,so H passivation is beneficial to obtain high performance AZO transparent conductive films.Compared with the AZO film,In,Ga co-doped ZnO films can significantly improve and improve carrier mobility,its value reached 24.01 cm2/Vs,but the carrier concentration is not high,only 2.74 x 1020 cm-3.XPS depth profile of elements of the ZnO film internal donor the can be speculated that doping mainly originates from the substitutional doping defects,rather than the O vacancy or interstitial Zn defects.Finally,the mechanism of impurity ion scattering,grain boundary scattering and polarization optical phonon scattering are discussed,and the inference and calculation formulas of each mechanism are determined.Through the electrical properties of temperature test of the ZnO,AZO and IGZO films,especially the different carrier mobility of films versus temperature on each scattering mechanism of the film.It is found that the migration rate of polarization optical phonon scattering is decreased rapidly with the increase of temperature,but the temperature rise to room temperature,the mobility is still far greater than 200 cm2V-1s-1,the limit of optical phonon scattering is not dominant.For the ZnO thin films,grain boundary scattering plays a major role in limiting the mobility of the IGZO thin films,due to the role of tunneling conductance,the impurity ion scattering is the main limiting mechanism.The thermionic emission mobility and electron tunneling mobility were closely related with the carrier concentration and defect density in grain boundary.So it is to say,the temperature,grain size,carrier concentration and grain boundary defect density all affect the carrier scattering mechanism of the films. |
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