A highly responsive UV photodetector based on hierarchical TiO2 nanorod/nanoparticle composite

Abstract

Hierarchical TiO₂ nanorod/nanoparticle composites were successfully prepared by TiCl₄ modification of vertically aligned TiO₂ nanorod (NR) arrays. After the hydrolysis of TiCl₄ at room temperature, TiO₂ nanoparticles (NPs) were deposited on the surface of TiO₂ NRs. Morphology and structure analysis demonstrated that the TiO₂ NPs were distributed around the entire surface of TiO₂ NRs due to the easy permeation of TiCl₄ solution between the NR space. Moreover, the high concentration of TiCl₄ and long reaction time are favorable for the generation of more TiO₂ NPs, which correspondingly increases the surface area of the composite to a large extent. Compared with most reported TiO₂-based UV photodetectors (PDs), the present TiO₂ NR/NP composite-based PDs simultaneously exhibit an extremely high response and a relatively fast response speed. The maxima of responsivity and response speed, which are 1973 A W⁻¹ and 0.47 s (rise time) and 1.02 s (decay time), respectively, are obtained from the sample of TiO₂ NR/NP-0.4 M-72 h. The fast and high photoresponses are ascribed to the large surface area provided by TiO₂ NPs, the well-defined electron transport pathway offered from TiO₂ NRs and the homojunction formed at the interface between them. Moreover, together with the high responsivity and the relatively fast response speed, significant UV light selectivity and a very good linear relationship between a photoresponse and the UV light intensity suggest that the present UV PDs are very competitive and highly applicable in UV light detection.