Reduced Persistent Photoconductivity in Successive Ionic Layer Adsorption and Reaction-Deposited ZnO:Sn Thin Films

Device-quality Sn-doped ZnO thin films are obtained from a simple and cost-effective successive ionic layer adsorption and reaction method with doping concentrations of 1, 3, 5, and 7 mol%. The influence of doping on the structural, morphological, and optoelectronic properties is studied. All the samples show a hexagonal wurtzite structure with planes that reorient themselves upon doping. Morphological studies reveal sharp cone-like structures branching out to become florets upon doping, resulting in a higher surface-to-volume ratio that is reflected in the photoresponse characteristics. The optical properties show a sharp absorbance edge, in the near-UV region, for all the samples. The calculated bandgap is in the range of 3.19–3.23 eV. Photoluminescence spectra are recorded to analyze the defect states in the samples, and the native defects of ZnO are found. A remarkable increase in current is observed upon illumination indicating significant photoresponse. ZnO tends to show persistent photoconductivity wherein there is delayed decay in the photocurrent. This phenomenon is reduced significantly herein by doping with Sn atoms. The spectral response study confirms that the devices are suitable for visible-blind, near-UV detection.