Structural and photoelectrical properties of AZO thin films improved by Ag buffer layers

Abstract

In order to obtain more excellent photoelectric properties of transparent conductive film, a series of high-quality AZO thin films and AZO/Ag/AZO thin films with various thickness values of Ag buffer layers are prepared on glass substrates by the radio frequency magnetron sputtering method at room temperature. The phase and surface morphologies of films are characterized by X-ray diffraction (XRD) and atomic force microscopy (AFM) respectively. The technology of Hall effect measurement and ultraviolet, visible spectrophotometer are employed to investigate the photoelectric properties of films. The electrical properties (including sheet resistance, sheet concentration and mobility) of films are also determined by using non isothermal technique to explore their thermal stability performances. The results indicate that the thickness values of Ag buffer layers have a large influence on the crystalline structures and photoelectric properties of AZO thin films. The XRD results show that with the increase of the thickness of Ag, the diffraction peak of Ag (111) is gradually enhanced, the ZnO (002) diffraction peak is gradually weakened, and the preferred orientation of ZnO (002) crystal plane is weakened. AFM test indicates that the change of Ag layer thickness has a great influence on the surface growth mode of the upper layer AZO thin film. When the Ag layer thickness is less than 5 nm, AZO thin film surface is rough and the grain size is smaller. When the Ag layer thickness is larger than 10 nm, the continuous surfaces of multilayer films begin to be shaped, directly affecte the photoelectric properties of the films. Hall effect measurement and transmittance test show that with the increase of Ag layer thickness, the transmission of AZO/Ag/AZO multilayer film gradually decreases, and also the resistance gradually decreases. When the thickness of Ag layer is 10 nm, AZO(30 nm)/Ag(10 nm)/AZO(30 nm) thin film gains a best figure of merit of 1.5910-1 -1 an average transmittance of 84.2% and a sheet resistance of 0.75 /sq. Hall effect measurement versus temperature indicates that AZO film without an Ag layer proves to be subjecte to the regular change of semiconductor resistance with temperature. When adding an Ag layer, the trend of the relationship of resistance with temperature presentes the characteristic of that metal resistance relating to temperature. Moreover, the sheet concentration of AZO with Ag layer is higher than that of AZO. The highest sheet concentration and the excellent thermal stability are obtained on AZO/Ag (10 nm)/AZO. The changes of the mobility of AZO under different temperatures turn out to be poorly stable. However, when adding an Ag layer, the better stability of AZO/Ag/AZO can be obtained. In conclusion, the photoelectric properties of films own excellent thermal stabilities with optimum thickness of Ag layer.