Electrical and ultraviolet-a detection properties of E-beam evaporated n-TiO2 capped p-Si nanowires heterojunction photodiodes

Abstract

Fabrication and Ultraviolet (UV) detection properties of p-Si Nanowires (NWs)/n-TiO2 thin film-based heterojunction photodiodes have been reported in this paper. The highly oriented, uniform and vertically aligned p-type single crystalline silicon nanowire (SiNW) arrays have been synthesized by the two-step process of electroless metal deposition and etching technique. A thin layer (∼120 nm) of anatase phase titanium dioxide (TiO2 ) is then deposited on the top of p-SiNWs using electron-beam evaporation technique. The surface morphology and crystallinity of p-SiNWs and n-TiO2 capped SiNWs have been characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction techniques. The optical properties of the as-deposited n-TiO2 thin film grown on p-SiNWs were analyzed using the photoluminescence measurements. The UV detection properties of the p-SiNWs/n-TiO2 heterojunction was studied by measuring the room temperature current-voltage (I - V ) characteristics under dark and UV illumination conditions with incident optical power (Popt ) 650 μWat wavelength (?) 365 nm. The as-fabricated p-SiNWs/n-TiO2 thin film heterojunction photodiode showed an excellent value of Detectivity ∼ 8.66 × 1011 mHz1/ 2W-1 with the external quantum efficiency (EQE) ∼ 79.33%, responsivity ∼ 0.234 A/W, and contrast ratio ∼ 113.82 at -11 V bias. Other parameters such as rectification ratio (∼ 519.82), Turn-on voltage (∼0.732 V) and effective barrier height (∼0.7924 eV) under dark condition were also calculated. The proposed p-SiNWs/n-TiO2 ) thin film hetrojunction can thus be explored for UV-A detection. © 2002-2012 IEEE.