Influence of ZnO thickness on electrical properties of SnO ₂ /ZnO heterojunction hydrogen sensor

Abstract We systematically investigated SnO 2 /ZnO n-n heterojunction hydrogen sensors with varying ZnO thicknesses fabricated by DC magnetron sputtering. Structural characterization confirmed successful bilayer formation with tetragonal SnO 2 and hexagonal wurtzite ZnO phases. The optimized SnO 2 /ZnO 100 nm sensor achieved improved performance with 58.8% response to 100 ppm H 2 at 270 °C, representing a 2.4-fold enhancement over pristine SnO 2 . The sensor exhibited fast response time of 3.7 s, and excellent linearity ( R 2 = 0.98) across 20–100 ppm. Enhanced sensing originates from synergistic n-n heterojunction effects creating interfacial electron depletion layers that facilitate efficient charge carrier modulation upon H 2 exposure. The optimal 100 nm ZnO thickness balances heterojunction interface effects with charge transport efficiency. This work establishes design principles for heterojunction-based hydrogen sensors applicable to fuel cell systems, industrial safety monitoring, and medical diagnostics.