Estudo comparativo de filmes finos de ZnO:Al e ZnO:Al:Ti depositados por magnetron sputtering e cátodo oco

Abstract

Current research has continuously been looking for new materials that present responses equivalent to semiconductors. These materials have a multifunctional character with associated effects between optical transparency and electrical resistivity. In this context, TCOs thin films are alternatives, which can meet specific demands due to their optical and electrical nature. This work investigated in a theoretical and experimental way the deposition of thin films of AZO (ZnO doped with Al) and TAZO (ZnO co-doped with Al and Ti) deposited by magnetron sputtering and hollow cathode. The synthesis of the films was performed with partial oxygen pressure varying between 0%, 15%, 25%, and 50%, respectively, concerning the total gas flow. The influence of gas on doping, microstructure, and physical properties of films was investigated. Magnetron sputtering depositions were performed by making a solid AZO target with 4% at Al and a solid TAZO target with 4% at and 2.5% at Al and Ti doping, respectively, in a flowing atmosphere with a maximum of 20 cm3/min, at a temperature of 90 ◦C and time of 0.5 h. The hollow cathode films were obtained from the same type of powder that gave rise to the targets used in magnetron sputtering. Hollow cathode depositions occurred with a maximum flow of 20 cm3/min, under a temperature of 200 ◦C, and a time of 0.5 h. X-ray diffraction identified that all films have a wurtzite structure and hexagonal crystalline system of the space group P63mc. The techniques of electron microscopy and atomic force allowed the observation of surface changes caused by the addition of oxygen to the treatment atmosphere, in addition to allowing the measurement of film thickness. All thin films produced in this work showed optical transmittance above 70% and electrical resistivity values that varied between 10−3 and 10−4 Ωcm. The calculation of geometry optimization corroborates the experimental results of XRD, which show the distortion in the octahedral sites of the ions Al3+ and Ti4+, giving rise to an asymmetric crystalline network with a low stoichiometric degree. The electronic structure of the bands made it possible to observe the arrangement of the valence and conduction bands as a function of the increase in oxygen in the network and the semiconductor state of the films, which present values of Eg close to the structure of pure ZnO and covalent nature of the ZnO (⊥ c).