Fast response of UV photodetector based on Ag nanoparticles embedded uniform TiO₂ nanotubes array

Titanium dioxide (TiO2) has drawn a potential research interest for ultraviolent (UV) photodetector (PD) applications because of its tunable bandgap in UV absorption region, low-absorption coefficient in visible region, n-type semiconducting property, and excellent chemical stabilities. In this study, attempts were made to explore the performances of TiO2 nanostructures such as nanotubes (NTs) and nanorods (NRs) based UV PDs embedded with 23 nm plasmonic silver (Ag) nanoparticles (NPs), which offer the local surface plasmonic resonance or near-field enhancement. The vertical TiO2 NTs and NRs with high uniformity and height of 1 µm were successfully synthesized using simple and low-cost electrochemical anodization and hydrothermal growth techniques, respectively onto Ti substrates. From the x-ray diffraction analysis, it was ascertained that the anatase phase has been formed for NTs, whereas the rutile phase dominated the NRs. All these nanostructures were characterized by various material characterization techniques such as field emission scanning electron microscopy, x-ray photoelectron spectroscopy, UV-vis-NIR and Raman spectroscopy to investigate their surface and structural morphologies and absorption spectra. Efforts were put to fabricate Ag/ (with or without Ag NPs) TiO2 nanostructures/ Ti based UV PDs, where Ag has been utilized as top electrode and Ti served the purpose for bottom electrode. The electrical characteristics such as current-voltage, responsivity, detectivity, external quantum efficiency, rise and decay times were systematically investigated under 365 nm UV light radiance. Among all the UV PDs, TiO2 NTs anchored with the Ag NPs offer better photocurrent, responsivity (1.37 AW-1), detectivity (5.18 x 1010 Jones), external quantum efficiency (465.42%), rise (0.43 s) and decay (0.70 s) times. In order to have better insight on the device operational principle, a band diagram was proposed and it was realized that desorption of oxygen ions, increment of free electron carriers, and localized surface plasmonic effect were responsible for obtaining improved photoresponse.