The growth mechanism of ZnO thin films deposited by an atmospheric pressure plasma jet (APPJ) is study. The APPJ used is sustained by a pulsed power source with a repetitive frequency up to 25 kHz using N2 or O2 as plasma gases. Nebulized zinc chloride solution is used as the precursor and is sprayed into the downstream of the plasma jet to deposit thin films on Si wafers. X-ray diffraction spectra show that the crystalline structure changes with the operating parameters, namely plasma gas flow rate and the applied voltage, which influence the jet temperature and reactivity. It is found that upon exposure of the precursor to the plasma jet, sheet-like zinc hydroxide chloride (ZHC) are formed first, and is converted to zinc oxide if the jet temperature is high enough. Under relatively low temperature, the conversion of the precursor end at ZHC. The grain size of the films is greatly influenced by the nucleation and growth rate. High jet temperature leads to a larger number of the nuclei and results in smaller grain sizes and denser ZnO thin films. O2 plasma jets are also utilized. Preliminary studies show that the O2 plasma jet is able to convert the precursor to ZnO thin films under optimized conditions. Finally, the key parameters that influence the electrical and optical properties will be identified.
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