UV-light-assisted gas sensor based on PdSe₂/InSe heterojunction for ppb-level NO₂ sensing at room temperature

The fabrication of van der Waals (vdWs) heterostructures mainly extends to two-dimensional (2D) materials. Nevertheless, the current processes for obtaining high-quality 2D films are mainly exfoliated from their bulk counterparts or by high-temperature chemical vapor deposition (CVD), which limits industrial production and is often accompanied by defects. Herein, we first fabricated the type-II p-PdSe₂/n-InSe vdWs heterostructure using the ultra-high vacuum laser molecular beam epitaxy (LMBE) technique combined with the vertical 2D stacking strategy, which is reproducible and suitable for high-volume manufacturing. This work found that the introduction of 365 nm UV light illumination can significantly improve the electrical transport properties and NO₂ sensing performance of the PdSe₂/InSe heterojunction-based device at room temperature (RT). The detailed studies confirm that the sensor based on the PdSe₂/InSe heterojunction delivers the comparable sensitivity (R_a/R_g = ∼2.6 at 10 ppm), a low limit of detection of 52 ppb, and excellent selectivity for NO₂ gas under UV light illumination, indicating great potential for NO₂ detection. Notably, the sensor possesses fast response and full recovery properties (275/1078 s) compared to the results in the dark. Furthermore, the mechanism of enhanced gas sensitivity was proposed based on the energy band alignment of the PdSe₂/InSe heterojunction with the assistance of investigating the surface potential variations. This work may pave the way for the development of high-performance, room-temperature gas sensors based on 2D vdWs heterostructures through the LMBE technique.