Preparation Of Al-F Co-Doped ZnO Thin Films By Sol-Gel Method And Study Of Their Properties

ZnO is one kind of oxide semiconductor material with wide band-gap and a hexagonal wurtzite structure.Due to its good photoelectric behavior,it is widely applied to various devices including solar cell,liquid crystal display as transparent and conductive oxide electrodes.ZnO materials without dopants can not meet these photoelectric devices,so we must dope purposely to enhance the carrier mobility to improve or adjust their properties.Some doping elements,for example,â…¢group elements(B,Al,Ga,In)orâ…¦group elements(F,Cl),can improve the conductive capability of ZnO thin films.Al-doped ZnO thin films(AZO)are widely studied as one of transparent conductive oxide materials with good future.Fluorine-doped zinc oxide(ZnO:F)thin films are also studied because the electronic concentration can be increased by incorporating Fluorine into Oxygen sites in the ZnO lattice and so the electrical properties of ZnO thin films can be enhanced.In our research work,the Al-F co-doped ZnO(ZnO:F:Al)thin films are deposited on glass substrates by sol-gel method.The crystal structure,resistivity and transmittance of thin films are mainly researched with various solution concentrations,annealing temperatures,annealing atmospheres and doping concentrations.X-ray diffraction(XRD),scanning electron microscope(SEM), spectrophotometer and four-point probe methods are employed to characterize and analyze the thin films.The results showed that ZnO:F:Al thin films prepared by sol-gel method have hexagonal wurtzite structure and the thin films are highly oriented along the C axis. The thin films with the 0.65M solution concentration have the best crystal structure. Doping concentrations and annealing process affect obviously the structural, electrical,and optical properties of ZnO:F:Al thin films.The electrical property of the thin films can be improved when doped with various doping concentrations (0.25at%～1.00at%),the electrical resistivity of thin films with the 0.75at%doping concentrations is the lowest.The annealing temperatures(450℃～650℃)and atmospheres(air,H₂,Ar,vacuum)affect the resistivity significantly.ZnO:F:Al thin films with 0.75at%doping concentrations,annealed at 550℃in the air have the strongest preferred orientation,uniform surface,mean optical transmittance over 90 %,the minimum resistivity of 1.02×10^-2Ω·cm.Annealing temperatures and atmospheres have little influence on the transmittance of ZnO:F:Al thins films; their mean optical transmittance is from 85%to 90%in the visible light region.