Fabrication and characterization of ZnO branched nanorods and ZnO/NiO heterojunction electrodes by chemical solution method

High quality ZnO nanorod arrays were synthesized by a two-step chemical bath deposition (CBD) on an ITO substrate. Our synthesis method is a two-step process: seeding and subsequent growth. The CBD was carried out in zinc acetate solution at 95 °C for 1 h, followed by thermal treatment at different temperatures. The structural and the optical properties of ZnO were investigated by X-ray diffraction, the scanning electron microscopy, and the optical transmission spectroscopy. The XRD results showed that the CBD ZnO nanorods have a hexagonal wurtzite structure with flat-tops as seen in SEM morphologies. The diameter of ZnO nanorods was found to be in the range 380–450 nm and the length was up to 1.3 μm depending on the thermal-treatment temperature. An average optical transmittance of more than 90% was obtained in the wavelength range 400–800 nm for the thermal temperature of 400 °C, where the length/diameter ratio reached a maximum value of 3.08. The ZnO branched nanorods fabricated by this two-step CBD at low temperature exhibited great crystal quality, leading to excellent electrical properties (ρ=3.2×10−3 Ω cm) and high carrier mobility (μ=40.4 cm2/V sec). Moreover, the current–voltage (I–V) characteristics of n-ZnO/p-NiO heterojunction electrode indicated that this nanostructure was rectifying in nature with low turn-on voltage and great rectification slope.