Role of defects in the electronic properties of Al doped ZnO films deposited by spray pyrolysis

Abstract

The best combination of electronic and optical properties in Al-doped ZnO (AZO) thin films have been archived by vacuum-based processing. However, vacuum-based processing is expensive. Solution processing, on the other hand, results in relatively higher resistivity. Methods are being looked to achieve low electrical resistivity and high transparency through scalable solution-based processing. In this study, pure and aluminium doped zinc oxide thin films were deposited on glass substrate by spray pyrolysis route. The deposited films were vacuum annealed for twenty minutes. Electrical, optical, morphological, and surface-specific properties of zinc oxide and aluminium doped zinc oxide thin film were investigated. The role of oxygen vacancies on the Fermi level and their effect on the conductivity of the films were analyzed. The Fermi level was at 3.21 and 3.31 eV for the pure and Al-doped films, which on vacuum annealing, increased to 3.27 and 3.4 eV, respectively. The work function of the as-deposited zinc oxide and AZO films were 5.65 and 4.38 eV, which on vacuum annealing decreased to 4.05 eV and 4.04 eV, respectively. A carrier concentration, as high as 1.7 × 1020 cm−3 with mobility 50 cm2/Vs and resistivity of the order of 2 × 10–3 Ωcm was achieved for 1 at.% Al-doped ZnO (AZO) film. At the same time, the transparency greater than 82% and a figure of merit 1.44 was achieved, which is one of the best reported values for solution-processed AZO films. © 2022, The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature.