Thin-film light-addressable potentiometric sensor with SnOx as a photosensitive semiconductor

In this study, a tin-based oxide (SnOx) semiconductor layer on a commercial indium tin oxide (ITO)/glass substrate was investigated for the first time for use as the active layer of a light-addressable potentiometric sensor (LAPS). The photoabsorption of SnOx layers sputtered using varying Ar/O-2 gas flow ratios was characterized by means of the ultraviolet-visible spectroscopy (UV-Vis); the photo/electric response of a LAPS directly covered with an NbOx sensing membrane was evaluated under modulated ultraviolet illumination. In situ substrate heating at 250 degrees C during sputtering and post-deposition rapid thermal annealing (RTA) with temperatures of 400 and 450 degrees C in a N-2 environment were applied to study sample behavior. Based on X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) results, the fabricated SnO2 layer can be transformed into a polycrystalline SnO2 phase in the bulk with a surface SnO layer by thermal budget. A high photocurrent and an acceptable pH sensitivity of 1.29 +/- A and 57.6 mV/pH, respectively, are obtained under UV light-emitting diode (LED) illumination for a LAPS built using a SnOx layer sputtered with a flow ratio of Ar/O-2 = 46/4 with substrate heating at 250 degrees C. The stability and lifetime performance of the SnOx LAPS needs to be improved by further process optimization, especially in terms of developing a crack-free SnOx process and increasing sensing membrane coverage. The experimental results show the potential of SnOx for use as the active layer in a LAPS.