Produção e caracterização de filmes finos de ZnO, intrínsecos e dopados com Al, para aplicação em eletrônica orgânica

Abstract

In this work, zinc oxide thin films intrinsic and doped with aluminum were grown onto glass substrates by RF magnetron sputtering technique at room temperature, aiming to study the influence of the deposition parameters and heat treatment in the electrical, optical and structural properties of these films. For this, two different targets were used: one of pure zinc oxide and other of zinc oxide doped with 2% of aluminum. The electrical, optical and structural characterization was made, respectively, by Hall effect, optical spectroscopy and X-ray diffraction measurements. It was observed that the deposition parameters – sputtering power, working pressure and argon flow – have a strong influence on the electrical and structural properties of the thin films. The optical properties, though, do not change with the above parameters, since all films had high optical transmittance in the visible region, which was more than 85% at 550 nm. The variation of these parameters allowed reducing the electrical resistivity of the films mainly because of the increasing of the carrier concentration of the ZnO thin films and the increasing of carrier mobility of the AZO thin films. All thin films exhibited hexagonal wurtzite structure preferably oriented in (002) plane along the c-axis perpendicular to the surface of the substrate. The improvement in the electrical properties and the fluctuation in the intensity of (002) peaks depend, mainly, on the energy of the atoms when ejected from the target during the sputtering process. Thin films with best electrical properties were obtained with sputtering power of 180 W, working pressure of 0.08 mbar and argon flow of 350 sccm. The best ZnO thin films had electrical resistivity of 2.07 x 10-4 Ωcm, mobility of 15.87 cm2/Vs, and carrier concentration of 1.95 x 1020 cm-3. The best parameters for the AZO film were 4.9 x 10-4 Ωcm, 5.9 cm2/Vs and 2.18 x 1021 cm-3 for resistivity, mobility and carrier concentration, respectively. The difference in the electrical properties is due to the presence of Al ions doping the ZnO matrix. With the optimization of the deposition parameters, ZnO and AZO films were then subjected to heat treatment, which increased electrical resistivity of the ZnO film and improved only in 5% the conductivity of the AZO film. Finally, we present the results on the characterization of an Organic Light Emitting Device (OLED) using an optimized AZO film as substrate.