Synthesis, characterization, and temperature-dependent electronic properties of ZnO nanorods using CBD techniques

High-quality and partially oriented ZnO nanorod films were synthesized by chemical bath deposition on top of a ZnO sol–gel spin-coating seed layer deposited on glass substrates. Two different ratios (0.625 and 6.25) of hexamethylenetetramine to zinc acetate were considered for the synthesis of the ZnO nanorod films and their optical, structural and electronic properties were studied. The ZnO nanorod films showed the wurtzite structure with a crystallite size about 50–55 nm, a dislocation density in the range of 10¹⁵ lines-m⁻² and a strain in the range of 10^–3. Energy dispersive spectroscopy and photoluminescence measurements indicated the existence of oxygen vacancies in the films. The ZnO nanorod films showed a bandgap energy about 3.24 eV. From photoluminescence results, an intense ultraviolet excitonic emission band was observed in the films. The films resulted with a carrier concentration in the range of 10¹⁵ and 10¹⁶ cm⁻³. From impedance spectroscopy measurements, a noticeable temperature-dependent electronic conductivity was observed, related probably to the nanostructured morphology of the films. In both films it was observed that the electronic conductivity decreased in the intermediate temperature region with the increment of temperature, probably due to chemisorption or desorption phenomena. But the electronic conductivity in the low and the high-temperature regions obeyed the grain boundary carrier-trapping model with the increment of the temperature, showing in both regions an activation energy close to 0.6 eV, attributed to the appearance of trap states due to the chemisorption of oxygen at the grain boundaries of the ZnO nanorods.