Ultraviolet sensing mechanism and characteristics of environmentally friendly aligned aluminium doped zinc oxide nanorod arrays prepared using low cost solution growth method M. H. Mamat* 1 , Z. Khusaimi 2 , M. Z. Musa 1 , M. F. Malek 1 and M. Rusop 1,2 Ultraviolet (UV) photoconductive sensors have been fabricated on glass substrates using aligned aluminium (Al) doped zinc oxide (ZnO) nanorod arrays at different annealing temperatures. The Al doped ZnO nanorod arrays were prepared using a novel technique of sonicated sol–gel immersion utilising Al doped ZnO nanoparticle thin film as seeded catalyst. In this study, the authors were able to increase the crystallinity of the Al doped ZnO nanorod arrays while maintaining the morphology of the Al doped ZnO nanorod after annealing process in ambient. The surface defects of the nanorod were significantly suppressed at high temperature up to 500uC, as can be observed in the photoluminescence spectra. It has been demonstrated that the photoresponse of the UV sensor under 365 nm UV illumination showed significant improvement after the annealing process due to the high crystallisation degree of the ZnO nanostructures. The influences of surface defects on the photoresponse properties of the fabricated UV photoconductive sensor are discussed. Keywords: UV photoconductive sensor, Aligned Al doped ZnO nanorod, Sonication, Sol–gel, Annealing temperature Introduction Zinc oxide (ZnO) is an environmentally friendly semi- conductor material with a direct bandgap energy of 3?3 eV and a large exciton binding energy of 60 meV. 1 It is a very useful and multifunctional material, which has been applied in nanoscale electronic and optoelectronic devices, including dye sensitised solar cells, 2 light emitting diodes, 3 gas sensors 4 and ultraviolet (UV) photoconduc- tive sensors. 5 Recently, a low dimensional structure, especially one-dimensional (1D) ZnO has been intensively studied due to its uniqueness and superior properties, such as high mobility, crystallinity and large surface area availability. These important characteristics might open a door towards the fabrication of highly efficient electronic devices. A sensing mechanism in a UV photoconductive sensor using ZnO nanostructures is largely influenced by its surface state. For example, the surface defects of ZnO may cause carrier trapping, high energy consumption and slow photoresponse of the sensors. 5,6 It is well known that nanostructured ZnO synthesised by a solution technique induces defects formation on its structure due to the low processing temperature. However, this solution technique is low cost, versatile and suitable for large scale fabrication. For this reason, the preparation of nanos- tructured ZnO by solution based deposition should not be neglected and should be optimised in order to minimise the defect concentrations in ZnO nanostructures, espe- cially for UV photoconductive sensor applications. There are certain techniques that can be used to treat a surface defect of ZnO, such as plasma treatment and annealing. 7,8 Annealing is a process where energy (usually thermal energy) is supplied to the material in order to change its physical and chemical properties. Although there are many reports on the effects of annealing on ZnO thin film, particularly granular shaped ZnO film, the report of annealing effect on the aligned ZnO nanorod film is still rare and debatable, especially on factors related with chemisorbed oxygen and ZnO properties, which are important in UV sensing characteristic. 8,9 Furthermore, our newly discovered preparation technique of aligned ZnO nanorod requires optimisation in the device fabrication process. 10 In order to fabricate highly efficient UV photoconductive sensor using a low cost method and to study the defect level of ZnO nanorod in our preparation technique, the study of annealing effects should be made. Hence, our objective in this research is to investigate the performance of UV photoconductive sensor using 1D ZnO thin film structure prepared at 1 NANO-ElecTronic Centre (NET), Faculty of Electrical Engineering, Universiti Teknologi MARA (UiTM), Shah Alam, Selangor 40450, Malaysia 2 NANO-SciTech Centre (NST), Institute of Science (IOS), Universiti Teknologi MARA (UiTM), Shah Alam, Selangor 40450, Malaysia *Corresponding author, email hafiz_030@yahoo.com S2-148 ß W. S. Maney & Son Ltd. 2011 Received 13 June 2010; accepted 1 April 2011 DOI 10.1179/143307511X13031890748650 Materials Research Innovations 2011 VOL 15 SUPPL 2