The impact of sputtering pressure on the TiO2/p-Si interface and its implications for hole-blocking and photodetection

Abstract

One convenient approach to minimize the surface recombination loss in Si is to passivate the surface dangling bonds by depositing a thin TiO2 layer on the bulk Si. Besides, the p-Si/TiO2 interface can initiate hole-blocking and facilitate efficient electron transport through the TiO2 layer; thereby, promoting the extraction of electrons for efficient onward utilization. In this context, the current investigation involves studying how the Ti3+ donor states, produced by deliberately introducing O-vacancies controlled by changing the plasma pressure in the RF-magnetron sputtering chamber during the growth of the TiO2 thin films, can change the material's Fermi level and work function and modify the band bending and band offset as well as the fixed oxide charge density in the p-Si/TiO2 heterojunction interface. The TiO2/p-Si interface has been studied through capacitance-voltage (C-V) analysis to determine the interface parameters such as fixed oxide charge, the density of interface traps, and the dielectric constant of TiO2. The studied hole-blocking property of the interface has been correlated to the photoresponsivity of the metal-oxide-semiconductor (MOS) structure. The MOS device fabricated at a pressure of 30 mTorr displays a large saturation current (15.95 μA cm–2) when subjected to a positive gate bias, facilitated by the relatively low conduction band offset (ΔEC ∼0.20 eV), significant positive fixed oxide charge (+1.18 ×1011 cm–2) and the interface trap density (1.03 ×1012 cm–2), which enhanced the transport of minority carrier electrons from the p-Si to the metal, resulting in a good photo responsivity ∼0.158 AW–1 and photo gain of ∼37.5 under white light illumination. Optimum hole-blocking and surface passivation characteristics of the TiO2/p-Si interface together may facilitate fabricating improved heterojunction Si solar cells.