Improving the photoresponse of magnetron sputtered titania films by optimizing substrate and electrode configuration

Abstract

Titania (TiO2) is a natural choice for photocatalysts and photodetectors due to its superior properties such as high stability and high photoelectric effect coupled with low cost fabrication routes. In this work we study the effect of substrate on the structural, morphological, and photoresponse behavior of sputtered titania thin films. We also compare the difference in photoresponse between parallel and series electrode configurations to understand the role of configuration on the design of photodetectors. TiO2 films of 50 nm thickness are sputtered onto three different substrates, namely quartz, fluorine-doped tin oxide (FTO), and silicon (Si) using direct current reactive magnetron sputtering. The structural and optical properties, along with photoresponse behavior, on these three different substrates are investigated. The sputtered TiO2 film crystallizes in the rutile structure with a uniform grain size distribution. Analysis of the transmittance data from UV–Vis spectra was used to derive the optical constants for the film. The sensitivity of TiO2 to photoresponse is highly dependent on the substrate. The response is better for Si substrate, when compared to FTO or quartz and this is due to the heterojunction formation at the TiO2/Si interface. Sensitivity, responsivity, and detectivity are also obtained for both parallel and series electrode configuration for Si substrate and better photoresponse is exhibited by the parallel configuration since carrier recombination in the bulk of the Si wafer is avoided. The photocurrent values in this work are an order of magnitude better than previous work on TiO2/Si, while the slightly slower response times maybe attributed to the strain-induced barrier reduction and band bending. Thus, this work showcases the tailoring of optoelectronic devices based on magnetron sputtered titania thin films by choosing appropriate substrates and electrode geometries.