A high-performance hydrogen sensor based on a reverse-biased MoS 2 /GaN heterojunction.

We report a MoS ₂ /GaN heterojunction-based gas sensor by depositing MoS ₂ over a GaN substrate via a highly controllable and scalable sputtering technique coupled with a post sulfurization process in a sulfur-rich environment. The microscopic and spectroscopic measurements expose the presence of highly crystalline and homogenous few atomic layer MoS ₂ on top of molecular beam epitaxially grown GaN film. Upon hydrogen exposure, the molecular adsorption tuned the barrier height at the MoS ₂ /GaN interface under the reverse biased condition, thus resulting in high sensitivity. Our results reveal that temperature strongly affects the sensitivity of the device and it increases from 21% to 157% for 1% hydrogen with an increase in temperature (25-150 °C). For a deeper understanding of carrier dynamics at the heterointerface, we visualized the band alignment across the MoS ₂ /GaN heterojunction having valence band and conduction band offset values of 1.75 and 0.28 eV. The sensing mechanism was demonstrated based on an energy band diagram at the MoS ₂ /GaN interface in the presence and absence of hydrogen exposure. The proposed methodology can be readily applied to other combinations of heterostructures for sensing different gas analytes.