Effect on the electrical and morphological properties of Bi incorporation into ZnO:Ga and ZnO:Al thin films deposited by confocal magnetron sputtering

This paper reports the effect on the electrical and morphological properties of co-doping ZnO thin films with Bi and Al or Ga. To do so, a confocal sputtering geometry was used with a Bi target and two intrinsically doped ZnO:Ga and ZnO:Al targets. By depositing at an intentional heating of 200 °C and applying a post-deposition thermal treatment at 350 °C and 300 °C, for ZnO:Ga,Bi and ZnO:Al,Bi, respectively, electrical resistivity values of 1.3 × 10−3 Ω cm and 4.8 × 10−4 Ω cm were achieved, with an optical transmittance above 80%. The X-ray diffraction data shows that all doped ZnO films have a wurtzite hexagonal structure with preferential crystal growth perpendicular to the (002) plane. The Seebeck coefficient was measured for the ZnO:Al,Bi films, where a maximum value of −48 μV K−1 was registered. The optimized electrical properties were correlated with the preferential crystalline texture along [001] and the corresponding current density applied to the Bi dopant target, J(Bi). ZnO:Al,Bi films present out-of-plane compression stress, which concomitantly increases with J(Bi), due to higher compact volume of unit cell with lower lattice parameter c when compared with the undoped ZnO. By controlling the incorporation of Bi, the deposition temperature and the post-deposition thermal treatment temperature, improvements on the thermoelectric power factor of ZnO:Ga and ZnO:Al thin films can be achieved.ilipe Correia is grateful to the Fundaçao para a Ci ~ ^encia e a Tec nologia 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 Develop ment Fund, through the Operational Programme for Competitive ness 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