| Al doped Zinc Oxide?AZO?,as a multifunctional material,exhibits excellent electrical,optical,magnetic,and sensitive performance.It is widely applied in electronic information industry and energy industry.AZO is represented the third generation of wide bandgap semiconductor after the first generation of semiconductor of silicon and the second generation of semiconductor of gallium arsenide.The semiconductor performance for AZO has been gradually developed and get more and more applications.As a typical electronic conductor,the electrical conductivity of AZO is mainly determined by the carrier concentration and Hall mobility.In the case of the solid solubility for zinc oxide is very low,the range of the carrier concentration becomes very narrow.Thus,the preparation of AZO material with high Hall mobility and low resistivity will be of great significance and application on the development of multifunction,low cost of electronic information industry.This paper reports the preparation of highly dense AZO ceramics in vaccum and argon atmosphere by field assisted sinteing technologh?FAST?,the influence of sintering conditions on relative density and microstructure have been investigated.In order to illustrate the sintering mechanism of AZO ceramic under field assisted sintering technologh and the interaction between the microstructure,property and thermal field,electric field,the distribution and evolution of thermal/electric filed during field assisted sintering are simulated by ANSYS.It is indicated that the densification for AZO ceramics under field assisted sintering is divided into two steps.Firstly,the highest temperature within the sample is below the densification temperature,the resistivity for sample is relatively high due to a large number of pores.The current is prevented to pass through the sample and the sample is heated derived from the thermal conductivity of graphite mould.Secondly,the highest temperature within the sample is exceeding the densification temperature,current passes through local compact region of the sample with low resistivity.In turn,the current passing through the sample promotes the homogeneity of temperature distribution,which contributes to the densification of AZO ceramics by alternate thermal/electric field coupling effects.Then,based on the densification mechanism of AZO ceramic during thermal-electric couple fields,we design the actions of pulse current on AZO ceramic to regulate the grain size and crystal defects.The influence of thermal-electric couple fields on grain size and crystal defects are investigated and the correlation between grain size,crystal defects and Hall mobility and resistivity is setup.The lowest resistivity of the AZO ceramic is 6.7×10-4??cm.In addition,by electric field assisted thermal deformation,the textured AZO ceramics with high c-axis orientation are fabricated which helps to establish the quantitative relationship between Hall mobility,resistivity and texture degree.The highest Hall mobility and lowest resistivity of textured AZO ceramic is 100.3 cm2·V-1·s-1 and 4.2×10-4??cm,respectively.The resistivity of textured AZO ceramic is decreased by 80%compared current literature reported.In addition,AZO composite ceramic with homodisperse graphene has been prepared by field assisted sintering which uses graphene as enhanced conductive phase.The effects of graphene on the miacrostructure and electrical property have been studied.The addition of graphene can reduce the densification temperature of AZO ceramic.However,the relative density of composite AZO ceramic is significantly deteriorated as the content of graphene is more than 0.05wt.%,which is attributed to the serious aggregation.The graphene are dispersed in the ZnO grain boundary and ZnO/ZnAl2O4/ZnO triangle grain boundary which form sandwich grain boundary of ZnO/graphene/ZnO and network structure between ZnO and ZnAl2O4.The graphene scattered in the grain boundary reduces the carrier scattering so as to improve the Hall mobility of AZO composite ceramics.Graphene also bridge the grains around the pores forming network structure which create multi-channel for the migration of carrier.AZO composite ceramics exhibit the highest Hall mobility of130.4 cm2·V-1·s-1 and lowest resistivity of 3.1×10-4??cm.Finally,transparent conductive films are fabricated by pulse laser deposition from AZO/graphene targets.The influence of deposition temperature,oxygen pressure and laser energy density was studied on structure and properties of thin films from AZO/graphene target.The lowest resistivity and highest optical transmittance of AZO film from AZO/graphene target is 3.1×10-4??cm and 91.5%,respectively.Compared with the AZO thin films from pure AZO target,AZO thin films from AZO composite target exhibit better crystallization at low temperature,lower resistivity and higher optical transmittance. |
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