“…Owning to its excellent physical properties, ZnO has been a promising material in piezoelectric and optoelectronic fields [3]. ZnO thin films are widely used to light-emitting diodes (LED) [4], UV sensors [5,6], solar cells [7,8], surface acoustic wave (SAW) devices and optical wave-guide devices as well [9]. It is well known that ZnO thin films can be prepared by variety of techniques such as sputtering [10,11], laser ablation [12][13][14], chemical vapor deposition [15,16] and sol-gel spin-coating technique [17][18][19][20][21].…”