Growth behaviors and characteristics of low temperature spin-sprayed ZnO and Al-doped ZnO microstructures

The influence of growth parameters of the spin-spray technique upon the microstructure and electrical and optical properties of ZnO and Al-doped ZnO microstructures was investigated. This investigation was carried out by varying the pH and concentration of the solutions utilized. With increasing pH from 9 to 12, the ZnO films changed from membrane-like microstructures at a pH of 9 to single crystal ZnO rods with hexagonal ends at the pH of 10, and to polycrystal ZnO needle-like tips with random crystalline orientation at the pH of 12. Varying the concentration of the solution brought about a dramatic change in the crystal growth behavior and crystalline orientation, with the least concentration producing rods more uniform and oriented in the c-axis direction. The optical absorption dependence of the ZnO microstructures was also studied by ultraviolet visible spectrophotometer. This investigation will enable optimized low temperature (<100 C) fabrication of ZnO films by the spin-spray technique with controllable microstructure and properties based on their processing conditions. Furthermore, the influence of Al doping on the electric property, optical property microstructures of the Al-doped ZnO thin films was examined. Increase in Al concentration from 0 to 2 % further reduced the resistivity of the ZnO films by 3 orders of magnitudes from 3.4 × 10 ⁴ to 14 Ω cm; while the Hall mobility increases from 1 to 140 cm²/V s at the same time. The optical photoluminescence measurement of Al-doped ZnO thin films in ultra violet (UV) was also demonstrated.