Core-Shell n-SnO2@p-SnO Heterojunctions via On-Chip Annealing for Ultrasensitive H2S Detection at Room Temperature

Conventional SnO₂-based gas sensors often suffer from high operating temperatures, excessive energy consumption, and dependence on noble metal catalysts. Here, we report a core-shell n-SnO₂@p-SnO heterojunction-based gas sensor, fabricated through a facile on-chip rapid annealing process of hydrothermally synthesized p-SnO nanoflakes drop-cast onto Ti/Au electrode-coated p-Si wafers, enabling efficient room-temperature H₂S detection. Under optimized on-chip annealing conditions, the p-SnO nanoflakes become encapsulated by compact layers of n-SnO₂ nanospheres (≈5–15 nm in diameter), forming a core-shell p-n heterostructure. This architecture induces synchronized modulations of the depletion layer thickness and space charge region width upon H₂S exposure, yielding a significantly enhanced response compared to conventional SnO₂/SnO composites. Furthermore, interactions between H₂S and hydrolysis products of adsorbed H₂O molecules release additional electrons, leading to humidity-enhanced sensing performance across a relative humidity range of 20–60%. The optimized sensor operates with excellent selectivity and stability at room temperature, achieving an ultrafast response time of 1 s — an unprecedented speed among SnO₂-based H₂S sensors — a high response magnitude of 66.7 toward 30 ppm H₂S, with a calculated detection limit of 0.85 ppm. Overall, this work demonstrates a novel, low-cost route for fabricating high-quality SnO₂@SnO heterojunctions and offers a promising pathway toward the development of high-performance room-temperature H₂S gas sensors.