Silicon-based long-wave infrared detectors for flammable gas sensing

Given the current industrial development trends, flammable gases are becoming increasingly important. However, the hazards associated with the storage and transportation of flammable gases pose risks to property and human life. Hence, there is an urgent need to develop gas sensors capable of instantaneous detection and operation at room temperature. In this study, we fabricated the first room-temperature silicon (Si)-based optical detectors for propylene (C₃H₆) and methane (CH₄), which have been reported to cause numerous deaths. The characteristic fingerprint absorption bands of C₃H₆ and CH₄ within the long-wave infrared (LWIR) region were used for gas sensing with hot-carrier-type Si-based photodetectors. Operating at room temperature and featuring a short response time of less than 1 ms, these sensors significantly reduced the risk of potential explosion hazards and enabled real-time detection. Detection of the asymmetric bending vibration at 7.8 μm provided more selectivity than that of the symmetric stretching vibration at 3.3 μm for carbon-hydrogen bonds in CH_4, enabling a clear distinction between flammable gases, such as CH₄ and C₃H₆. Additionally, the sensor demonstrated a limit of detection (LOD) for C₃H₆ and CH₄ well below their respective explosion threshold. The combination of a short response time and low LOD confirms the capability of the sensor to provide an early warning of gas leakage.