Growth of Al-doped ZnO films with tilted nano-columns on r-cut sapphire substrates by pulsed laser deposition

2wt.% Al2O3-doped ZnO (AZO) thin films in both single layer and bi-layer forms were deposited on alpha-Al2O3 (01(1)over-bar2) (r-cut) and (0001) (c-cut) substrates by a pulsed laser deposition technique. Single layer AZO films were grown under either vacuumor 33.3Pa of O-2 pressure. Bilayer AZO films were grown with a sequential deposition of a uniform template layer under vacuum and a nano-column-structured layer under 33.3 Pa of O-2 pressure. Interestingly, single layer AZO film grown on r-cut sapphire in high oxygen pressure (33.3 Pa) shows tilted grain boundaries along [(1)over-bar10(2)over-bar](AZO). The bilayer film deposited on r-cut substrate shows tilted nano-column growth while the film grown on c-cut substrate has vertically grown nano-columns. The results of X-ray diffraction and cross-section transmission electron microscopy studies show a systematic variation of the d-spacing of (0002)(AZO) and (11(2)over-bar0)(AZO) for all AZO films. Electrical resistivity was measured and found to be strongly dependent on the different microstructures achieved under different oxygen pressures and substrates. (C) 2012 Elsevier B. V. All rights reserved.