Three-terminal-controlled field-effect resistive hydrogen sensor

Based on a Pd/oxide/AlGaAs pseudomorphic high-electron-mobility transistor (PHEMT) structure, an interesting three-terminal-controlled field-effect resistive hydrogen sensor is fabricated and studied. The influences of gate-source bias (V_GS) on the hydrogen sensing properties are presented in this work. Experimental results show that the V_GS bias significantly affects the resistance sensitivity, conductance variation, current variation, transient response, pressure-dependent and -independent rate constants, and response and recovery time constants. At 30 °C, a significant resistance response (S_R = 100 × (R_air - R_H2) / R_air) of 33.3% (82.8%) to 4.3 (9970) ppm H₂/air is obtained at V_GS = -0.6 V. Nevertheless, the largest conductance variation (ΔG) appears to be in the range between V_GS = -0.3 and -0.4 V. An empirical equation is derived to explain the consistency between the calculated data and experimental results. Good linear relationship is observed between current variation and temperature under different V_GS biases. The transient response at V_GS = -0.3 V shows larger current variations, accompanying the longer response and recovery time constants than those at V_GS = 0 V. Furthermore, on the basis of a kinetic adsorption analysis, the hydrogen pressure-dependent and -independent rate constants are obtained.