Quasi-Reference Electrode-Integrated Dual-Metal-Gate AlGaN/AlN/GaN HEMT for the Detection of Mercury Ions (Hg²⁺)

In this study, we designed and fabricated a Dual Metal Gate (DMG) AlGaN/AlN/GaN High Electron Mobility Transistor (HEMT) for the detection of mercury ions. The device features an extended gate electrode integrated with a quasi-reference electrode for biasing applications. The extended gate region was functionalized with thioglycolic acid to form a semi-assembled monolayer that acts as a receptor for mercury ions. The device design, sensing methodology, and working principle of the proposed sensor have been discussed and analyzed in terms of its sensitivity, linearity, limit of detection (LoD), and limit of quantification (LoQ). The device demonstrated a drain current sensitivity of 2.22 mA/mm·ppb at a gate-source voltage (V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">GS</sub>) of 0 V and a drain-source voltage (V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub>) of 0.5 V. The LoD and LoQ were found to be 1.46 ppt and 4.86 ppt, respectively, at V<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">DS</sub> 0.5 V. Sensitivity analysis was conducted by varying the drain and gate voltages to achieve maximum performance. Additionally, we evaluated gate leakage and performed time-dependent analyses to examine the stability of the device over extended measurement periods.