White light-driven photo response of TiO2 thin films: Influence of substrate texturing

Abstract

In this work, the role of film thickness on white light-driven photo response and electrical properties of TiO2/Si heterojunctions is investigated. Two types of substrates, viz. pristine- and chemically prepared pyramidally textured-Si are used for simultaneous growth of TiO2 films using radio frequency (RF) magnetron sputtering technique. X-ray diffraction study reveals the amorphous nature of as-grown TiO2 thin films. In addition, it is observed that the surface reflectance of conformally grown TiO2 overlayers on textured-Si substrates can be brought down to 0.73% for 5 nm and 0.77% for 20 nm, whereas in case of pris-Si substrates it is 40% for 5 nm and 30% for 20 nm-thick films (in the wavelength range of 400–800 nm). Further, TiO2/Si heterostructures exhibit diode-like rectifying behavior under both dark and white light illumination. The 5 nm-thick films exhibit very low photoactivity in terms of photocurrent, whereas 20 nm-thick films show a remarkable enhancement in the photocurrent up to 10.25 and 78.68 μA (under reverse bias) when grown on pris-Si and txt-Si substrate, respectively. In addition to the transient photocurrent, the responsivity and sensitivity are also higher for 20 nm-thick films. These results are explained in terms of change in their optical and electrical properties. The present finding will be certainly important for fabricating high speed optoelectronic devices based on reverse biased TiO2/Si heterojunctions.