P-type ZnO thin film deposited by spray pyrolysis technique: The effect of solution concentration

The aim of this research is to study the role of concentration variations on precursor solution of nitrogen doped ZnO (ZnO:N) thin films which has been prepared by spray pyrolysis technique. SEM micrographs show that ZnO:N films in 0.1 ML concentration have a mono-disperse surface with nano-spheres of 50 nm in diameter. In higher molarities the nano-spheres agglomerate leading to particle formation. For 0.4 ML concentrations this change is observed, where plume like particles are seen over the surface of ZnO:N thin film. This change corresponds also to changes observed in the XRD spectra, where crystal orientation of ZnO:N thin films changes from (002) to (100). All of the ZnO:N thin films have kept their sharp ultra violet absorption edge, but the transparency in visible spectra region decreases as the molarities in precursor solution increase. Photoluminescence spectra at room temperature revealed emissions at 2.33 eV, 2.54 eV and 3.16 eV that can be attributed to the presence of nitrogen in ZnO structure. We also observe that all samples analyzed show a p-type Hall effect behavior, and that as the molarities in the precursor solution increase, the electrical resistivity of the films decreases, due to an enhancement of free carriers, while the mobility decreases. These data prove the capability of spray pyrolysis as a viable technique in preparing p-type TCO materials and so, fully transparent CMOS-like devices. (C) 2009 Elsevier B.V. All rights reserved.