Formation of ZnO thin films consisting of nano-prisms and nano-rods with a high aspect ratio by a hydrothermal technique at 60 °C

ZnO thin films that consist of elongated nano-prisms and nano-rods were successfully grown on 100 nm-thick ZnO seeded glass substrates by hydrothermal synthesis at 60 °C and pH 10.3 in an aqueous solution containing Zn(NO3)·6H2O, Al(NO3)3·9H2O, Na3-citrate and NH4OH. The effect of Al(NO3)·6H2O and Na3-citrate, as surfactant chemicals, on the structural, morphological, optical and electrical properties of ZnO thin films were investigated. X-ray diffraction results showed that all the deposited films were grown as a polycrystalline wurtzite hexagonal phase with a c-axis preferred, out-of-plane orientation and without unwanted second phase. ZnO thin films deposited without any surfactant chemicals or deposited only with Al(NO3)·6H2O consist of elongated needle shaped nano-rods with a very rough surface morphology. On the other hand, ZnO thin films prepared using Na3-citrate as a surfactant chemical consist of hexagonal nano-prisms with a very smooth surface morphology. The thickness of the ZnO thin films with the very smooth surface morphology was increased remarkably using both Na3-citrate and Al(NO3)·6H2O as surfactant chemicals, in which ZnO thin films consisted of elongated hexagonal nano-prisms. These results show that relatively thick ZnO thin films with a good surface morphology can be grown easily by the appropriate use of surface modifying chemicals, such as Na3-citrate and Al(NO3)·6H2O. The photoluminescence results showed strong defect-related emission peak centered near 545 nm in the rough surfaced ZnO thin film grown without any surfactant chemicals and strong band-edge peak centered near 368 nm in the smooth surfaced ZnO thin film grown using both Na3-citrate and Al(NO3)·6H2O as the surfactant chemicals.