Fabrication of highly sensitive room temperature operated NO2 gas sensor using back gated 2D-MoS2 FETs

Atomically thin layered semiconductors such as Molybdenum Sulphide (MoS₂) have emerged as potential candidate for trace level detection of chemicals owing to their innate very high surface to volume ratio. Present work focuses on the fabrication of room temperature operated Nitrogen dioxide (NO₂) gas sensor exploiting MoS₂ as gas sensing matrix. Three different sensor structures, (i) Au/Cr/single layer MoS₂/Si₃N₄/Si, (ii) Au/Cr/four-layer MoS₂/Si₃N₄/Si, and (iii) Au/Cr/ten-layer MoS₂/Si₃N₄/Si were fabricated and gas sensing measurements were carried out for different NO₂ gas concentrations (1 ppm to 500 ppm). Effect of NO₂ gas adsorption on MoS₂ surface was explained using realignment of energy band diagram. Sensing response (%) for Au/Cr/four-layer MoS₂/Si₃N₄/Si structure was found to be maximum as compared to the case of single layer and ten-layer structure and corresponding sensing mechanism has been investigated in detail. Response and recovery time of fabricated Au/Cr/four-layer MoS₂/Si₃N₄/Si sensor were found to be 24 s and 41 s respectively, and cross selectivity measurements were performed and sensor was found to be highly selective towards NO₂ gas. Present work pave the way to realize the potential of MoS₂ based back gated Field Effect Transistors (FETs) for fabricating highly efficient NO₂ gas sensors.