| AZO thin film has special optoelectronic properties which include a wide band gap,high optical transmittance in the visible spectrum region and low resistivity,so there is a good prospect of reality and potential application in many areas.As there are a wealth of raw materials of AZO thin film,we needn't be worry about the resource depletion and high prices once it is used widely.In this paper,the AZO target was prepared by the method of solid-phase sintering.The sintering curve was determined by the analysis of TG-DSC curve of AZO powder,and the shrinkage of the target was calculated.AZO thin film was prepared by RF magnetron sputtering,the composition of AZO thin film and AZO powder were analyzed by EDS.The most optimum parameters were found by the effects of target-substrate distance,sputtering angel,annealing temperature and annealing time on phase structure,electrical properties,optical properties and figure of merit of AZO films.the effects which were investigated by means of XRD,HALL and UV.The main experimental results are as follows:(1)The sintering curve was set by analysis of TG-DSC curve of AZO powder.The key is heat preservation when the temperature is 1250?,1300?and 1450?.The temperature was maintained at 1250? for 4 hours,which would dissolve edge of tissue and enhance the strength of the target.The temperature was maintained at 1300? for 1 hours,which would make the material of grain boundary spread to the grain gap.The temperature was maintained at 1450? for 3.5 hours,which would promote the recrystallization and remove residual glue to improve the densification of the target.The target shrinkage was 8.25%.(2)By the analysis of AZO thin films,the atomic ratio of Al atoms to Zn atoms is slightly different from the stoichiometric ratio,but the deviation is slight,and Al atoms are basically doped according to the stoichiometric ratio.Compared with the EDS analysis of AZO powder,it was found that the sintering of the target greatly promoted the uniform mixing bewteen Al2O3 and ZnO.(3)Through the analysis of the properties of AZO thin films which were prepared by different target-substrate distance,it was found that the most optimum parameter of target-substrate distance is 13cm(the minimum target-substrate distance),the figure of merit and the deposition rate of AZO films are the maximum.With the increase of the target-substrate distance,the grain size gradually decreases,the film stress gradually increases,the crystal quality gradually deteriorates,the deposition rate gradually decreases.The above phenomenons are due to multiple collision between sputtering atoms and Ar+,which results in energy of sputtering atoms is small when they reach the substrate,even sputtering atoms can not reach the substrate,even if the sputtering atoms reach the substrate,the low migration and diffusion of sputtering atoms will affect the deposition rate and the quality of film.With the increase of the target-substrate distance,the resistivity of the films gradually increase,when the target-substrate distance is 13cm,the lowest resistivity of AZO films is 1.13×10-2?·m.When the resistivity is the lowest,the carrier concentration is the largest,but the mobility is not the maximum.The maximum mobility is obtained when the target distance is 16cm,which is determined by the ionized impurity atom scattering and grain boundary scattering.With the increase of the target-substrate distance,the average optical transmittance of the films gradually increase,and all of them are above 92%.As the crystal quality is the best when the target-substrate is 13cm,the optical transmittance is not minimum.The unusual phenomenon that the optical band gap Eg ranges from 3.48eV to 3.60eV,and it increases with the increase of the target-substrate distance,which is due to the quantum size effect.(4)Through the analysis of the properties of AZO thin films which were prepared by different sputtering angel,it was found that the most optimum parameter of sputtering angel is 50°,the figure of merit of AZO films is the maximum,and the deposition rate is better.With the increase of the sputtering angel,the grain size gradually increases,the film stress gradually decreases,the crystal quality gradually improves,as the sputtering projected area is the largest,the deposition rate is maximum when the sputtering angel is 40°.With the increase of the sputtering angel,the resistivity of the films gradually decreases,when the sputtering angel is 50°,the carrier concentration and the mobility of the films make the resistivity be the lowest,the lowest resistivity of AZO films is 1.13×10-2?·m.Generally,The average optical transmittance of the films gradually decreases,but the average optical transmittance of the film is the minimum when the sputtering angle is 40°,as the sputtering projected area is the maximum,which results in the film is thickest.So the optical transmittance increases when the sputtering angle is 50°.In addition,the average optical transmittance of all the films are above 92%.The optical band gap Eg ranges from 3.56eV to 3.61 eV,which is consistent with the variation of carrier concentration.(5)Through the analysis of the properties of AZO films which are annealed at different annealing temperatures,it was found that the most optimum parameter of annealing temperature is 400?,and the figure of merit of AZO film is maximum.With the increase of the annealing temperature,the grain size gradually increases,the film stress gradually decreases,the crystal quality gradually improves.With the increase of the annealing temperature,the resistivity of the films gradually decrease(decrease by an order of magnitude),according to ?=1/?=n?e,the resistivity of the films gradually decrease,which is due to the carrier concentration and mobility gradually increase.With the increase of the annealing temperature,the increase of carrier concentration is due to the increase of the number of oxygen vacancies,the increase of mobility is due to grain growth.The lowest resistivity of prepared AZO film is 1.39×10-3?·m.The average optical transmittance of the film is improved after annealing,which is due to Burstein-Moss effect of the ultraviolet absorption edge,and the decrease of grain boundary scattering which caused by the growth of grain.The ability of the increase of the optical transmittance of the films decreases with the increase of annealing temperature,which is due to the increase of the number of oxygen vacancies,the oxygen vacancies will be defective structure which results in defect scattering.When the annealing temperature is 450C,the optical transmittance of annealed sample is lower than the unannealed sample,which is due to the increase of the oxygen defect and the abnormal growth of grain.The abnormal growth of grain will make the rate of light scattering increases.In addition,the average optical transmittance of all the films are above 89%.The optical band gap Eg ranges from 3.54eV to 3.77eV,and it increases with the increase of annealing temperature,which is the result of the increase of carrier concentration.The optical band gap Eg of AZO film whose annealing temperature at 450C is lower than the optical band gap Eg of AZO film whose annealing temperature at 400 ?,which is due to abnormal grain growth and the saturation of oxygen defect,which make the defect band widened and forbidden band narrowed.The PL spectra of the AZO films which is annealed at 300? were compared with the PL spectrum of the AZO films which is unannealed.The results showed that the film has Burstein-Moss effect,the point defects were decreased,and the number of oxygen vacancies was increased.(6)Through the analysis of the properties of AZO films which are annealed at different annealing time,it was found that the most optimum parameter of annealing time is 60min,and the figure of merit of AZO film is maximum.With the increase of the annealing time,the grain size increases and then decreases,the film stress gradually decreases,the crystal quality improves and then deteriorates.With the increase of the annealing time,the carrier concentration decreases,and the mobility increases and then decreases.In this section,the variation of carrier concentration and mobility make the resistivity of AZO films decrease and then increase,the minimum resistivity of AZO film is 1.63×10-3?·m when the annealing time is 60min.The average optical transmittance of the film increases and then decreases,when it gradually increases,which is mainly due to the ionized impurity scattering and the decrease of grain boundary scattering which caused by the growth of grain.The optical transmittance of the film decreases when the annealing time is further increased,which is caused by the weak of Burstein-Moss effect of the ultraviolet absorption edge and the increase of the grain boundary scattering which caused by decrease of the grain size.In addition,the average optical transmittance of all the films are above 89%.The optical band gap Eg of the AZO film ranges from 3.55eV to 3.77eV,and it increases and then decreases.when it gradually increases,which is due to that the interstitial Zn atoms get enough energy to return to the crystal lattice and makes the defect band narrowed and forbidden band widened.when it gradually decreases,which is due to the decrease of carrier concentration and the increase of the grain size(the increase of the grain size makes defect band widened). |
PDF Full Text Request