Plasmon assisted high ultraviolet to visible broad band photosensitivity in lateral Ag NPs-TiO2 nanocomposite film

Abstract

Noble metal-TiO2 composite films attract great attention because of the extension of its spectral absorption in the visible range due to surface plasmon resonance. Among them, Ag-TiO2 composite is considered to be an ideal candidate for the visible light photosensitivity because of narrow energy distribution of plasmonic hot electrons in Ag and the high density of states in the TiO2 conduction band. Here, we report high broad band photosensitivity from ultraviolet (UV) to visible wavelength of sol-gel grown TiO2 film decorated with Ag nanoparticles (NPs) in a simple planar photoconductive geometry. In addition to UV light, Ag NPs-TiO2 composite film (for 1 nm Ag) shows very high photosensitivity values of ∼105 and ∼104 and responsivity values of 0.1 A/W and 7×10−3 A/W at 10 V bias for 680 nm and 550 nm illuminations respectively while pristine TiO2 show photosensitivity values of 6×102 and 3.3×102 and responsivity values of 2.4×10−4 A/W and 6.6×10−5 A/W for both the visible illuminations. A highly enhanced broad band photosensitivity due to transfer of plasmonically generated hot electrons from Ag to TiO2 is quite interesting without having any device fabricated. The photosensitivity values for Ag NPs for 3 nm and 6 nm layer thicknesses on TiO2 decrease because of coalescence of metal NPs on surface which acts as scattering center and/or light shielding.