Preparation And Optoelectrical Properties Of TMZO Transparent Conductive Oxide Thin Films

With the rapid development of semiconductor industry,transparent conductor oxide?TCO?thin film has been more and more applied in these fields,such as solar cells,touch panels and flat-panel displays.So far,indium tin oxide?ITO?is still the main TCO materials in most of industrial fields.However,taking into account the high cost due to the scarcity of indium?In?,it is urgent to seeking new TCO materials instead of ITO thin films and other alternative TCO materials have been explored extensively.Among these materials,zinc oxide?ZnO?which is a new type of II-VI semiconductor material has been considered as one of the most potential alternatives for ITO,because of the abundant reserves,low cost,excellent optoelectronic,piezoelectric and ferroelectric properties.Especially,the optical and electrical properties of ZnO film can be improved by doping other elements.Although there were a lot of researches which had been carried out on the single element doping of ZnO,the study on the two elements codoping of ZnO film is still very limited.In this study,titanium-magnesium co-doped ZnO?TMZO?thin films were deposited on quartz glass substrates by radio-frequency magnetron sputtering technique using a sintered ceramic of ZnO mixed with MgO and TiO₂ as a target.The mass fraction of the TMZO ceramic target is:96 wt%ZnO,2 wt%TiO₂,2 wt%MgO.The influence of substrate temperature,working pressure and sputtering power on the microstructure and optoelectronic properties of TMZO films was investigated.The main works and conclusions are shown as follows:?1?On the basis of genetic algorithm and spectral fitting theory,the adaptive genetic algorithm spectrum fitting program has been designed and used to solve the optical constants,include refractive index?n?,extinction coefficient?k?and thickness?d?of the deposited films.Then,the calculation results were also determined by envelope method and scanning electron microscope?SEM?,respectively.The results obtained by these methods are consistent,which indicates that the fitting program is effective and creditable.Meanwhile,compared with other methods,the adaptive genetic algorithm spectrum fitting program is running faster and more suitable for many kinds of thin films.?2?The influence of different process parameters on optical and dielectric properties of TMZO thin films was investigated.All the properties were measured by photometer,spectral fitting program and other optical characterization techniques.The results show that the average transmittance in the visible region(T_av)is above 90%.Moreover,the value of refractive index n ranges from 1.9 to 2.4,the extinction coefficient k is very small in the visible range and rises rapidly in the ultraviolet region.Due to the Burstein-Moss effect,the maximum value of the optical band gap of the film is Eg=3.48 eV.The dispersion behavior of refractive index was analyzed by the Sellmeier's dispersion model.It is found that the refractive index dispersion curves of thin films obey the single-oscillator model.?3?The electrical resistivity,carrier concentration and mobility were determined by the Hall effect measurement system.The results indicate that the electrical resistivity decreases first and then increases with the increase of the process parameters.The optimum resistivity is?=8.05×10^-3?·cm,and the corresponding values of carrier concentration and mobility are N_e=1.63×10²⁰ cm^-33 and?=4.77 cm²·V^-1·s^-1,respectively.?4?Through the studies of optical and electrical properties of thin films,this conclusion can be obtained that the optoelectronic properties of TMZO thin films could be affected by process parameters.The figure of merit is FOM=1.17×10³?^-1·cm^-11 under the optimum process conditions.It is obvious that strict control of process parameters is beneficial to the preparation of high performance TCO films.?5?All the prepared films are polycrystalline with a hexagonal wurtzite structure and preferential orientation of c axis.The best crystallizing quality is obtained under the optimum process parameters.?6?Based on the investigation of the microstructure and optoelectronic properties of the TMZO thin films,the optimum deposition conditions were obtained and given as follows:substrate temperature,300°C;working pressure,0.6 Pa;sputtering power,200 W;target-substrate distance,75 mm;and sputtering time,25 min.