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 degrees 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 fiat-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 mu m 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 degrees 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 (rho=3.2 x 10(-3) Omega cm) and high carrier mobility (mu=40.4 cm(2)/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. (C) 2010 Elsevier B.V. All rights reserved.