An investigation into the modification of low temperature deposited ZnO thin films by different annealing processes has been undertaken using laser, thermal and rapid thermal annealing of 60nm ZnO films deposited by Hi-Target-Utilization-Sputtering. Single pulse laser annealing using a KrF excimer laser ( A = 248nm) over a range of fluences up to 315 mJ/cm2 demonstrates controlled indepth modification of internal film microstructure and luminescence properties without the film degradation produced by high temperature thermal and RTA processes. Photoluminescence properties show that the ratio of defect related deep level emission (DLE, 450nm -750nm, 2.76eV-1.65eV) to excitonic near band-edge emission (NBE at 381nm, 3.26eV) is directly correlated to processing parameters. Thermal and rapid thermal processing results in the evolution of a strong visible orange/red DLE photoluminescence (with peaks at 590nm, 2.10eV and 670nm, 1.85eV) dominated by defects related to excess oxygen. At higher temperatures, the appearance of a green/yellow emission (530nm, 2.34eV) indicates a transition of the dominant radiative transfer mechanism. In contrast, laser processing removes defect related DLE and produces films with intense NBE luminescence, correlated to the observed formation of large grains (25-40nm).
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