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.