Effects Of Aluminum Doping Content On The Optical And Eletrical Properties Of ZnO Thin Films

Recently,Al doped ZnO film (ZnO:Al) is a promising transparent conductive film because of its satisfactory electrical and optical properties, low cost of raw materials and stability in hydrogen plasma environment.ZnO:Al thin film as electrode materials commonly used in photovoltaic devices and OLED devices. Low resistivity and high visible light transmittance are two important factors which can impact on electrode materials. In order to reduce the film resistivity, usually make an appropriate amount of aluminum ions into the ZnO lattice. Aluminum doping content increases concentration of crystal free carrier, thereby enhancing the conductivity properties of ZnO thin films. If the Al doping level is low, the film conductivity can not increase; if Al doping is too high, the excess Al atoms into the lattice not only reduce the carrier concentration and mobility, but also as a lattice scattering Center lower film transmittance in visible region. Can be seen only in the amount of aluminum doping range, can the film both excellent optical and electrical properties. Therefore, the inquiry on Al doped ZnO:Al thin film optical properties is particularly important.In this paper, the transparent and conductive AZO films were deposited on glass substrate by DC reactive magnetron sputtering from Zn/Al alloy targets doped with 1,2 and 3wt.%and ZnO/Al2O3 ceramic target doped with 2wt.% Al2O3, respectively. The effect of deposition parameters on the structural, electrical and optical properties of AZO films was investigated systematically by scanning electron microscopy (SEM), PANalytical x-ray diffractometry (XRD), four point probe,UV-VIS-IR spectrophotometry and HMS-3000 Hall effect measurement system,respectively. The results indicate:(1) Effect of substrate temperature on the electrical properties of ZnO:Al thin films with different Al-doped content was investigated. The results showed that with the increasing dopant content the substrate's optimum reaction temperture lowers,at 230℃,210℃,180℃when the resistivity corresponds to a minimum. Respectively, 6.3×10-4Ω·cm,7×10-4Ω·cm and 1×10-3Ω·cm. (2) Select the same resistivity of ZnO.Al thin film samples with different Al-doped content to study the optical properties. The results showed that in the UV band the blue shifts of the optical absorption edge occurred with the increasing doping concentration. Moreover, in the near-infrared band (800-1100nm) 1wt.% transmittance of AZO was significantly higher than 2,3wt.% of the films. This is mainly because high carrier concentration produces undesirable infrared (IR) absorption by free carriers.(3) Select the same resistivity of ZnO:Al thin film samples with different Al-doped content to study the electrical properties include carrier concentration and carrier mobility rate by HMS-3000 Hall effect measurement system. The results showed that as the doping increases, the film carrier concentration gradually increased, but the film carrier mobility rate gradually decreased. We mixed scattering mechanism and the mobility of mechanisms to give an explanation.(4) With 2wt.% Al-doped ceramic target preparation of ZnO:Al thin films to study the substrate temperature on the thin film photovoltaic performance. The results showed that with the substrate temperature increasing, the film resistivity decreased gradually. When the substrate temperature is 390℃, the resistance reached the lowest rate of 4.7×10-4Ω·cm. Then with 2wt.% Al alloy target prepared doped ZnO:Al thin-film comparison of temperature on the resistivity of their impact. The results showed that the ceramic target of the AZO thin films prepared by different alloy target prepared AZO films when the substrate temperature is 210℃, the lowest resistivity of up to 6.74×10-4Ω·cm. Once the deviation from this temperature resistivity of the will increase. We are from the alloy target by reactive sputtering, and ceramic target in the sputtering mechanism to give an explanation.(5) Systematic study of substrate temperature on lwt.% ZnO:Al thin film resistivityobtained when the substrate temperature of 230℃, the resistivity minimum, resistance to 6×10-4Ω·cm. Then, this sample as an anode applied to the OLED device, and with the same resistivity of the ITO anode prepared by the efficiency of OLED devices for comparison. The results showed that both devices showed typical diode characteristics. However, from the current density, luminance and current efficiency point of view of three aspects, AZO thin film devices are less than the ITO thin film anode anode device performance. The reason is a preliminary analysis of the work function of AZO thin films slightly less than the work function of ITO thin films, leading to the anode hole injection capacity and relatively cheap.