SILAR-deposited nanostructured ZnO thin films: effect of deposition cycles on surface properties

ZnO thin films were deposited onto the glass substrates using successive ionic layer adsorption and reaction (SILAR) technique by varying the deposition cycles from 25 to 100 in steps of 25 cycles. The effect of deposition cycles on the structural, morphological, optical and electrical properties was investigated and reported. Structural analysis revealed the formation of the hexagonal wurtzite crystal structure of ZnO with the preferential plane orientation of (1 0 0) for all deposition cycles. For the film deposited at 25 cycles alone, we observed the meagre diffraction peak at 2θ = 21.27° corresponds to (1 0 1) plane of the orthorhombic phased zinc sulphate, which indicated the incomplete formation of zinc ammonium complex from the precursor. Morphological analysis revealed the formation of nanorod-like morphology for the deposition cycles of 25 and 50, whereas it was found to be deformed at 75 and 100 cycles. The optical bandgap of the deposited thin films was decreased as a function of deposition cycles. However, at 75 deposition cycles, the bandgap was increased to 3.2468 ± 0.0026 eV, and it could be attributed to the variation in the density of states near the conduction band. The significant variations in the electrical parameters namely, carrier concentration, mobility, electrical resistance as a function of deposition cycles were investigated. The variations in the refractive index and static impedance characteristics as a function of deposition cycles were also studied and reported.