Characterization of sputtered ZnO films under different sputter-etching time of substrate

Polycrystalline ZnO films are prepared using radio frequency magnetron sputtering on glass substrates which are sputter-etched for different time. Both the size of ZnO grains and the root-mean-square (RMS) roughness decrease, as the sputter-etching time of the substrate increases. More Zn atoms are bound to O atoms in the films, and the defect concentration is decreased with increasing sputter-etching time of substrate. Meanwhile, the crystallinity and c-axis orientation are improved at longer sputter-etching time of the substrate. The Raman peaks at 99 cm-1, 438 cm-1 and 589 cm-1 are identified as E2(low), E2(high) and E1(LO) modes, respectively, and the position of E1(LO) peak blue shifts at longer sputter-etching time. The transmittances of the films, which are deposited on the substrate and etched for 10 min and 20 min, are higher in the visible region than that of the films deposited under longer sputter-etching time of 30 min. The bandgap increases from 3.23 eV to 3.27 eV with the increase of the sputter-etching time of substrate.