ZnO main epilayers are deposited with three-pulsed precursors in every growth cycle at 100 degrees C on various thicknesses of 300 degrees C-grown homo-buffer layers by atomic layer deposition (ALD) on sapphire substrate. Samples are treated without and with post-deposition rapid thermal annealing (RTA). Two different annealing temperatures 300 and 1000 degrees C are utilized in the ambience of oxygen for 5 min. Extremely low background electron concentration 8.4 x 10(14) cm (3), high electron mobility 62.1 cm(2)/V s, and pronounced enhancement of near bandgap edge photoluminescence (PL) are achieved for ZnO main epilayer with sufficient thickness of buffer layer (200 ALD cycles) and post-deposition RTA at 1000 degrees C. Effective block and remove of thermally unstable mobile defects and other crystal lattice imperfections are the agents of quality promotion of ZnO thin film. (C) 2017 Elsevier B.V. All rights reserved.