Thermal stability of sol-gel p-type Al-N codoped ZnO films and electric properties of nanostructured ZnO homojunctions fabricated by spin-coating them on ZnO nanorods

The thermal stability of sot-gel p-type Al-N codoped ZnO films was investigated by high-resolution X-ray photoelectron spectroscopy (XPS). XPS revealed the chemical bonding states and solubility of N-related complex defects in the ZnO films. The concentrations of N-O and (NC)(O) varied with annealing temperature, which led to the change in conduction between p-type and n-type. Variable-temperature Hall-effect measurement showed that N-O acted as a shallow acceptor, with its energy level locating at similar to 114 meV above the valance band maximum. Transmission electron microscopy confirmed the presence of undesired carbon clusters as a graphite state in the ZnO films. In order for Al-N codoped ZnO films to exhibit p-type conductivity, samples could only be annealed in a certain range of temperatures. A hybrid structure with nanostructured ZnO homojunctions was fabricated by spin-coating the p-type Al-N codoped ZnO film on an n-type ZnO nanorod array (ZNA). The hybrid nanostructure was demonstrated to possess rectification behavior characteristic of a p-n junction. The leakage current of the nanostructured ZnO homojunctions was smaller by a factor of 2 than that of the film-based ZnO homojunction at a reverse bias of 5 V. The p-type ZnO film/n-type ZNA structure can be applied as a versatile p-n optoelectronic device. (C) 2012 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.