Combination of nitrogen mediated crystallisation with post-deposition annealing-Towards ultra-thin ZnO:Al contacts

In order to improve the performance of doped zinc oxide thin films, the combination of a seed layer approach based on Nitrogen Mediated Crystallisation (NMC) with the post-deposition annealing of functional ZnO:Al films under a protective a-Si:H capping layer was applied in this work. The seed layers were prepared by magnetron sputtering and the effects of deposition parameters like power density, pressure and nitrogen content in the sputtering gas are reported. Optimised NMC seed layers were covered by ZnO:Al layers whose electrical transport properties have been investigated. Combination of these two approaches allowed decreasing resistivity to ≤ 350 μΩ cm and increasing charge-carrier mobility up to > 60 cm2/V s for 230-280 nm thick films. Apparently, NMC-seed layer assists better relative crystallites' orientation, i.e. better out-of-plane texture, whereas the applied annealing helps to release the residual stresses in the film and decreases the concentration of scattering defects in ZnO:Al layers.