| In order to improve the photoelectric properties of ZnO films, we prepared ZnO thin films doped by two kinds of metals based on traditional technology groundwork about preparation of ZnO films with metal and non-metallic co-doping. Al-doped, La-doped, Al-Na co-doped and La-Na co-doped ZnO thin films were prepared by sol-gel method. The structure, transmittance and electric conductivity of the films before and after doping were studied.The results reveal that Al, La, Al-Na, La-Na doping could improve the conductivity of ZnO thin films, in which the effect of Al-doped is most significant.The dopant concentration has great effect on resistivity of ZnO films, generally, there is a "U"-type variation about resistivity which is declining initially but rising later with the increasing amount of doping elements. With single metal doping, when consistency of Al3+ ion is 1.2mol%, the lowest resistivity of films is 0.112Ω·cm-1; When consistency of La3+ ion is 0.35mol%, the lowest resistivity of films is 1.84Ω·cm-1. It is also observed that the resistivity of Al-doped and La-doped films is lower than that of Al-Na and La-Na co-doped films. Annealing temperature plays a important role in conductivity of ZnO films, with the increase of annealing temperature, the resistivity of Al-doped, La-doped and La-Na co-doped ZnO films intend to rising, but the resistivity of Al-Na co-doped films is declining. Compared with Al-Na co-doped and La-Na co-doped ZnO films, Al-doped and La-doped films have better transmittance with average level 83% in the ultraviolet-visible.SEM images reveal that La-doped and La-Na co-doped ZnO thin films have obvious trend that the grain size is increasing with the increase of dopant concentration, and the trend is more apparent than before when the annealing temperature is higher than 450℃. XRD structural analysis indicate that crystalline and (002)-oriented ZnO films were obtained at three kinds of annealing temperatures such as 450℃,500℃and 550℃whatever dopant is single metal or two kinds of metals. The c-axis was oriented in various directions as well as the perpendicular direction to the substrate surface.The peak position and intensity of (002) orientation moved with small part in comparison with ZnO undoped, same condition have happened in (100) and (101) orientation, this phenomenon shows that there is dopant ion in ZnO crystal lattice.Metal doped ZnO system calculation results of Materials Studio software reveals that the ZnO lattice was forced to distort with metal doping and the increase of unit cell parameters is due to the cell system change which is decided by ionic radius from the doping element. The larger ionic radius, the stronger change. To a certain degree, We can explain the experimental fact that resistivity of ZnO thin film doped with Al and Na element is higher than that in Al doped ZnO system after results analysis about density of states and band gap calculation of system that Zn bit is replaced by single metal and that two Zn bit are replaced by two kinds of metals in ZnO cell model.
|
PDF Full Text Request