Preparation And Performance Optimization Of ZnO Transparent Conductive Films

ZnO is a wide band-gap semiconductor,the conductive performance of ZnO films can be greatly improved by doping with Ga or Al.Reserving with rich raw materials,ZnO has emerged as one of the most important transparent conducting oxides(TCO) for a variety of promising applications such as thin-film solar cell,flat panel liquid crystal display devices,and infrared(IR) reflector in recent years.In this paper ZnO transparent conductiving thin films were grown on glass substrate by DC reactive magnetron sputtering.The contents of this paper included ZnO:Ga single-layer films and multilayer structure films combined with Cu films and ZnO films.Improve the electrical and optical properties of ZnO transparent conductiving films by changing the process parameters and using experiment design methods.The main results are obtained as follows:1.Multi-factors experimental design method was introduced in the study of ZnO transparent conductiving thin films.We applied the Taguchi design method on the optimization of the electrical properties of ZnO:Ga films which deposited by DC reactive magnetron sputtering. Four influential deposition parameters,such as oxygen partial pressure,argon partial pressure, substrate temperature and sputtering power were selected in this experiment.The results showed that this method greatly simplifies the optimization of complicated multiple parameters.It has been showed that the experimental gases made a total contribution about 80%and were the most influencing parameters on the electrical properties of ZnO:Ga films.By Taguchi method,highly conductive ZnO:Ga films have been prepared,with the resistivity of 2.6×10^-4Ω·cm and the transmittance of nearly 90%in the visible region.The properties of the ZnO:Ga films rival those of commercially available ITO,and show great application prospects.2.We reported the effect of the substrate temperature on the structural,electrical and optical properties of ZnO:Ga films prepared by DC reactive magnetron sputtering in a wide temperature range from room temperature up to 400℃.The crystallinity and surface morphology of the films are strongly dependent on the growth temperatures,which in turn exert an influence on the electrical and optical properties of the ZnO:Ga films.The film deposited at 350℃exhibited the relatively well crystallinity and the lowest resistivity of 3.4×10^-4Ω·cm.On the other hand,for low-temperature applicantions we tried to get low-resistance and higt-transmittance ZnO:Ga films at 150℃by changing the sputtering powers.When the sputtering power increased to 160W, the properties of the films deposited can be improved.The minimum resistivity of the film was 1.3×10^-3Ω·cm.3.ZnO:Ga/Cu,ZnO:Al/Cu and ZnO:Ga/Cu/ZnO:Ga multilayer structure films were deposited by dc reactive magnetron sputtering at room temperature.The electrical and optical properties of the films are deeply correlated with Cu thickness.The electrical properties of ZnO films were improved greatly by introducing an ultrathin Cu underlayer,while retaining transmittance values acceptable for optoelectronics application.A figure of meritφ_TC was defined to evaluate the quality of different transparent conductive films.All the multilayer structure films achieved the highest quality with a Cu layer thickness of 7.5nm.The influence of annealing temperature on the properties of ZnO:Ga/Cu multilayer structure films had also been studied.The results show the electrical and optical properties of the multilayer structure films will be improved when it is annealed in Vacuum.After annealed at 400℃,the multilayer structure show a resistivity of～10^-5Ω·cm,an average visible transmittance of 80%,and good near-IR reflective behavior.