Photo-assisted aromatic VOC sensing by a p-NiO:Li/n-ZnO transparent heterojunction sensor element

A p-NiO/n-ZnO transparent heterojunction diode is prepared by the continuous film deposition using RF magnetron sputtering technique and processed into a chemical sensor element by photolithography patterning and chemical etching. The inter-digital sensor arrays have pn junction interfaces facing the atmosphere and its I–V response is slightly modified by the introduction of VOCs (volatile organic compounds) under dark. The sensor performance for aromatic VOCs is extremely enhanced under deep UV light (λ = 254 nm) irradiation and the photo-current rapidly decreases as a function of VOC concentrations. The photo-driven electron transport between photo-excited VOC adsorbates and valence band (VB) of p-NiO is essential to the VOC sensing in this system.