Ultrasensitive Indium Phosphide Nanomembrane Wearable Gas Sensors

Air quality is deteriorating due to continuing urbanization and industrialization. In particular, nitrogen dioxide (NO₂) is a biologically and environmentally hazardous byproduct from fuel combustion that is ubiquitous in urban life. To address this issue, we report a high-performance flexible indium phosphide nanomembrane NO₂ sensor for real-time air quality monitoring. An ultralow limit of detection of ~200 ppt and a fast response have been achieved with this device by optimizing the film thickness and doping concentration during indium phosphide epitaxy. By varying the film thickness, a dynamic range of values for NO₂ detection from parts per trillion (ppt) to parts per million (ppm) level have also been demonstrated under low bias voltage and at room temperature without additional light activation. Flexibility measurements show an adequately stable response after repeated bending. On-site testing of the sensor in a residential kitchen shows that NO₂ concentration from the gas stove emission could exceed the NO₂ Time Weighted Average limit, i.e., 200 ppb, highlighting the significance of real-time monitoring. Critically, the indium phosphide nanomembrane sensor element cost is estimated at <0.1 US$ due to the miniatured size, nanoscale thickness, and ease of fabrication. With these superior performance characteristics, low cost, and real-world applicability, our indium phosphide nanomembrane sensors offer a promising solution for a variety of air quality monitoring applications.