Multifactorial investigations of the deposition process – Material property relationships of ZnO:Al thin films deposited by magnetron sputtering in pulsed DC, DC and RF modes using different targets for low resistance highly transparent films on unheated substrates

We present a comprehensive study of the many parameters available in magnetron sputtering (including sputtering modes and target choice) to obtain low-resistivity ZnO:Al (AZO) films. The material is widely studied by many groups, however most of the reports focus on the optimization of one parameter, making the translation to another system cumbersome. We aimed to provide a general blueprint for a quick optimization of the process parameters for low resistivity, high crystalline quality AZO films. We found that it was the total argon pressure that controlled the outcomes most and that it is very important to have it the lowest possible. We show that the deposition power and other parameters do not influence the films in such a way. We tested two different (black and white) AZO targets and also did not found many differences, which may also be relevant for the researchers starting their work and wondering if the target they ordered would work well. We obtained very low film resistivities, at 1.2 mΩcm while depositing at room temperature, which is comparable with state-of-the-art results for deposition on heated substrates. We argue, that the sputtering configuration with a short target to substrate distance is responsible for this, opening up the way for low resistivity AZO deposition on heat-sensitive substrates.