Porous Si nanowires for highly selective room-Temperature NO₂ gas sensing

We report the room-Temperature sensing characteristics of Si nanowires (NWs) fabricated from p-Si wafers by a metal-Assisted chemical etching method, which is a facile and low-cost method. X-ray diffraction was used to the the study crystallinity and phase formation of Si NWs, and product morphology was examined using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). After confirmation of Si NW formation via the SEM and TEM micrographs, sensing tests were carried out at room temperature, and it was found that the Si NW sensor prepared from Si wafers with a resistivity of 0.001-0.003 Ω.cm had the highest response to NO₂ gas (R_g/R_a = 1.86 for 50 ppm NO₂), with a fast response (15 s) and recovery (30 s) time. Furthermore, the sensor responses to SO₂, toluene, benzene, H₂, and ethanol were nearly negligible, demonstrating the excellent selectivity to NO₂ gas. The gas-sensing mechanism is discussed in detail. The present sensor can operate at room temperature, and is compatible with the microelectronic fabrication process, demonstrating its promise for next-generation Si-based electronics fused with functional chemical sensors.