Compositional analysis by RBS, XPS and EDX of ZnO:Al,Bi and ZnO:Ga,Bi thin films deposited by d.c. magnetron sputtering

Rutherford backscattering spectrometry, X-ray photoelectron and X-ray energy dispersive spectroscopies were employed to analyse Bi incorporation into ZnO:Al and ZnO:Ga transparent and electrically conductive thin films deposited by d.c. magnetron sputtering, with thickness in the range of 300–400 nm. Sputtering was performed in an argon atmosphere from two targets in confocal geometry being one composed of either ZnO:Al2O3 or ZnO:Ga2O3 composites and the other a Bi metal target. The content of bismuth dopant in the ZnO matrix was controlled by the respective target current density (JBi) in order to attain a high optical transparency (>80%) in the visible region. For ZnO:Al,Bi films Bi content varied from 0.1 to a maximum of 1.5 at.% when varying JBi from 0.06 to 0.26 mA cm−2. However, for ZnO:Ga,Bi films, deposited in similar conditions, Bi reached a maximum overall layer content of 2.4 at.%, with a surface enrichment content that varied from 1.3 to 8.8 at.%. It was also observed that the Bi content in the topmost layers of the films is slightly depleted due to thermal evaporation upon thermal annealing in vacuum at 350 °C. It is envisaged applications for these films as transparent photoelectrodes and thermoelectric materials.Fundação para a Ciência e a Tecnologia (FCT, Portugal)/PIDDAC through the Strategic Funds project reference UID/FIS/04650/2013. Filipe Correia is grateful to the Fundação para a Ciência e a Tecnologia for the Ph.D. Grant SFRH/BD/111720/2015. Paulo Salvador is grateful to the Project WinPSC - POCI-01-0247-FEDER-017796, for the research grant, co-funded by the European Regional Development Fund (ERDF), through the Operational Programme for Competitiveness and Internationalisation (COMPETE 2020), under the PORTUGAL 2020 Partnership Agreement. Joana Ribeiro is grateful to University of Minho for the Grant UMINHO/BI/66/201