A route for an improved hydrogen sensing window using ZnO decorated Pt/AlGaN/GaN HEMT sensors

H2 has received considerable attention as an alternative energy source. The detection of H-2 is necessary for its safe use due to its explosive flammability. Pt/AlGaN/GaN HEMT can detect H-2 gas by a shift in the threshold voltage (V-th) induced by the formation of a dipole layer upon H-2 exposure. However, using the Pt/AlGaN/GaN HEMT, the change of Vth after H-2 exposure is as small as-0.35 V, indicating a narrow sensing window (delta V-th) for H-2 detection. This can cause a detection failure in the case of a dynamically fluctuating gas over time. Here, we demonstrate a significantly widened sensing window of delta V-th (1.8 V) using an extremely thin (~ 1 nm) ZnO layer grown by atomic layer deposition on the Pt/AlGaN/GaN HEMT sensors. The enlarged sensing window of delta V-th originated from a decreased work function of ZnO on the Pt gates, which further shifted Vth in the negative direction and led to the formation of a dipole layer upon H-2 exposure.