NO2 Gas Sensor Based on SnSe/SnSe2p-n Hetrojunction

Abstract

Air pollution is a big concern as it causes harm to human health as well as environment. NO2 can cause several respiratory diseases even in low concentration and therefore an efficient sensor for detecting NO2 at room temperature has become one of the priorities of the scientific community. Although two dimensional (2D) materials (MoS2 etc.) have shown potential for NO2 sensing at lower temperatures, but these have poor desorption kinetics. However, these limitations posed by slow desorption can be overcome, if a material in the form of a p-n junction can be suitably employed. In this work, ~150 nm thick SnSe2 thin film has been deposited by thermally evaporating in-house made SnSe2 powder. The film has been studied for its morphological, structural and gas sensing applications. The morphology of the film showed that the film consists of interconnected nanostructures. Detailed Raman studies further revealed that SnSe2 film had 31% SnSe. The SnSe-SnSe2 nanostructured sensor showed a response of ~112% towards 5 ppm NO2 at room temperature (30 °C). The response and recovery times were ~15 seconds and 10 seconds, respectively. Limit of detection for NO2 was in sub-parts per million (sub-ppm) range. The device demonstrated a better response towards NO2 compared to NH3, CH4, and H2. The mechanism of room temperature fast response, recovery and selective detection of NO2 independent of humidity conditions has been discussed based on physisorption, charge transfer, and formation of SnSe-SnSe2 (p-n) nano-junctions. Depositing a nanostructured film consisting of nano-junctions using an industrially viable thermal evaporation technique for sensing a very low concentration of NO2 is the novelty of this work.