Further investigation of a hydrogen-sensing Pd/GaAs heterostructure field-effect transistor (HFET)

Based on a GaAs-based heterostructure field-effect transistor (HFET) equipped with a catalytic Pd gate, an interesting Pd/GaAs transistor-type hydrogen sensor is fabricated and studied. A simple model is used to elucidate the on-state and off-state behaviors in the transistor operation. In air and N₂ environments, hydrogen-induced effect not only causes an obvious current variation in the saturation region, but also results in a drastic change of sensor response in the cut-off region. The further analyses of electrical characteristics are also presented. The calculated values of I_DS operating regime (>0.8 g_m,max) are 115.3 (115.1) and 108.2 (106.2) mA/mm in air (N₂) and 1% H₂/air (1% H₂/N₂), respectively. The variation trend of g_m under the positive gate bias is contrary to that under the negative gate bias in hydrogen-containing ambiance. In addition, the decrease in on-off current ratio (I_on/I_off) towards hydrogen gas is attributed to the considerable variation of I_off in the cut-off region.