Contents lists available at ScienceDirect Solar Energy journal homepage: www.elsevier.com/locate/solener White light-driven photo response of TiO 2 thin films: Influence of substrate texturing Ranveer Singh a,b , Mohit Kumar a,1 , Mahesh Saini a,b , Biswarup Satpati c , Tapobrata Som a,b, ⁎ a SUNAG Laboratory, Institute of Physics, Bhubaneswar 751 005, Odisha, India b Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai 400 085, India c Surface Physics and Materials Science Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata 700 064, India ARTICLE INFO Keywords: TiO 2 thin films p-Si Textured-Si Photoresponse Heterojunctions ABSTRACT In this work, the role of film thickness on white light-driven photo response and electrical properties of TiO 2 /Si heterojunctions is investigated. Two types of substrates, viz. pristine- and chemically prepared pyramidally textured-Si are used for simultaneous growth of TiO 2 films using radio frequency (RF) magnetron sputtering technique. X-ray diffraction study reveals the amorphous nature of as-grown TiO 2 thin films. In addition, it is observed that the surface reflectance of conformally grown TiO 2 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, TiO 2 /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 TiO 2 /Si heterojunctions. 1. Introduction Oxide semiconductor-based heterojunctions have attracted tre- mendous attention as a driving element for the next-generation display devices such as high speed (> 250 Hz) and large scale (> 50 in.) liquid crystal displays (LCDs), flexible displays, photodetectors, and light- emitting diode (LED) displays because of their unique optical and elec- trical properties (Ahn et al., 2015; Hosono, 2006; Martins et al., 2007). For example, Xie et al. (2015) have demonstrated SnO 2 /CuO-based visible-blind ultraviolet photodetectors (PDs) with peak responsivity of 10.3 AW -1 at a low bias of 0.2 V. Likewise, ultraviolet–visible (UV–Vis) photo detectors (PDs) based on transition metal oxides are very im- portant devices which offer a lot of versatile applications (Hosseini et al., 2016; Hsu et al., 2012). Among various transition metal oxides, TiO 2 has attracted the attention of researchers for generation of solar hydrogen and photocatalysis by virtue of its photo stability, chemical stability, high photo conversion efficiency, and non-toxicity (Chang et al., 2012; Fujishima and Honda, 1972; Maeda et al., 2007; Singh et al., 2017; Wang et al., 2011). However, due to its wide band gap, it is able to absorb only 5% light out of the whole solar spectrum, albeit by doping and/or making a heterojunction with narrow band gap materials (e.g. Si) it is possible to extend the absorption of light even in the visible region (Hsu et al., 2012). A heterojunction between two different materials is found to be present in a variety of nanostructures such as core-shell nanowires (Chueh et al., 2007; Goldberger et al., 2006; Mieszawska et al., 2007), bilayered composite nanoribbons (Yang et al., 2016), etc. and exhibits huge potential for applications in solar cells (Yang et al., 2016), photo- detectors (Hosseini et al., 2016), charge storage devices (Padilha et al., 2016), and light-emitting diodes (Gudiksen et al., 2002). For instance, in order to improve the photo- to dark-current ratio and achieve fast re- sponse of a photodiode, a combination of different materials such as Cu 2 O/TiO 2 , TiO 2 :N/C, TiO 2 :Cr/ZnO, and TiO 2 :Nb/Si are used (Chang et al., 2012; Dao et al., 2013; Gautam et al., 2016; Tsai et al., 2011; Wang et al., 2012). For the growth of TiO 2 thin films, several physical vapour deposi- tion techniques are in commonplace such as pulsed laser deposition, https://doi.org/10.1016/j.solener.2018.08.086 Received 27 April 2018; Received in revised form 13 August 2018; Accepted 30 August 2018 ⁎ Corresponding author at: SUNAG Laboratory, Institute of Physics, Bhubaneswar 751 005, Odisha, India. 1 Present address: Department of Electrical Engineering, Incheon National University, 119 Academy Rd. Yeonsu, Incheon 22012, Republic of Korea. E-mail address: tsom@iopb.res.in (T. Som). Solar Energy 174 (2018) 231–239 0038-092X/ © 2018 Elsevier Ltd. All rights reserved. T