Nano-gap Effects in Semiconductor Gas Sensors

Abstract

The effect of gap size on the gas sensitivity of semiconductor gas sensor was evaluated in the NO₂ sensing using WO₃ nanosensor, the Cl₂ sensing using In₂O₃ nanosensor and the H₂S sensing using SnO₂ nanosensor. The nano-gap effect was markedly observed in the NO₂-WO₃ system and the Cl₂-In₂O₃ system (resistance increase), while the H₂S-SnO₂ system showed the weak nano-gap effect. This difference resulted from the ratio (S_i/S_gb) of sensitivity at semiconductor oxide-electrode interface (S_i) to at grain boundary (S_gb). The NO₂-WO₃ and the Cl₂-In₂O₃ systems showed the large S_i/S_gb ratio (32-43), while the small ratio (9.7) was obtained in the H₂S-SnO₂ system at the gas concentration of 0.5-1 ppm. It was found that the clearer nano-gap effect was obtained for the system having the larger S_i/S_gb ratio. In the system having large S_i/S_gb ratio, the nano-design of electrode structure like nano-gap electrode was important for high sensitivity gas sensors.