Characterization of Transparent Conductive ZnO Thin Films Prepared by an Atmospheric Pressure Plasma Jet
Date Issued
2012
Date
2012
Author(s)
Li, Hsin-Chieh
Abstract
Deposition of transparent and conductive ZnO thin films by an atmospheric pressure plasma jet (APPJ) is studied. 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 or glass substrates. By using N2 plasmas, lower resistivity can be obtained comparing with those obtained using O2 plasmas. X-ray diffraction spectra show that the crystal structure changes with the operating parameters, namely plasma gas flow rate and the applied voltage, which influence the jet temperature and reactivity. Under an applied voltage of 275 V and a flow rate of 30 slm, dense and smooth films can be deposited. ZnO films with a resistivity of 13 Ω-cm and an average transmittance of 80% between 400 and 800 nm can be obtained.
The growth mechanism of ZnO thin films deposited by the APPJ is proposed. 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.
We study the influence of the carrier gas flow rate on the properties of ZnO thin films. The results show that the resistivity is lowest as carrier gas flow rate is 500 sccm. In our work, the effect of the Al or In doping on the electrical properties of ZnO thin films do not improve the conductivity of ZnO thin films.
Subjects
atmospheric pressure plasma jet
ZnO thin films
TCO
aluminium doped ZnO
spray pyrolysis
nebulizer
Type
thesis
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