Improved optical properties of ZnO thin films by concurrently introduced interfacial voids during thermal annealing

We report the influence of size controlled interfacial voids on the optical properties of non-epitaxial polycrystalline ZnO films grown by atomic layer deposition. Interfacial voids generated due to nanoscale Kirkendall effect [A. D. Smigelskas and E. O. Kirkendall, Trans. AIME 171, 130, (1947)], along the ZnO-Al2O3 interface, enhanced the ratio of near band edge to defect luminescence of ZnO films up to eight folds. This improvement is attributed to stress relaxation caused by formation of interfacial voids that allowed greater grain growth within the polycrystalline ZnO films upon annealing. Larger crystals have a lower surface-to-volume ratio profile which lessens the defect emission by decreasing surface effects on the optical properties of ZnO. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3609321]