On a Pd/InAlAs metamorphic high electron mobility transistor (MHEMT)-based hydrogen sensor

Hydrogen sensing characteristics of a Pt/AlGaN/GaN heterostructure field-effect transistor (HFET) prepared by sensitization, activation, and electroless plating (EP) approaches

“…Table 3 lists a comparison between the studied EP Pt-gate HFET and other HFETs. As compared to other works [34][35][36][37][38][39]42,45], the studied EP Pt-gate HFET presents robust thermal stabilities and excellent hydrogen sensing performance. Notably, the significantly high rectification ratio R of the studied EP Pt-gate HFET demonstrates superior switching performance under hydrogen-contained ambiences.…”

“…However, the response time constant under a hydrogen concentration of 10,000 ppm H 2 /air is longer than that under a 1000 ppm H 2 /air gas. This might be attributed to the overshoot phenomenon [42]. The relatively longer response time is principally affected by the irregularly high transient response under the 10,000 H 2 /air ambience.…”

“…In order to investigate the on-off switching performance of the EP Pt-gate HFET under hydrogen-contained ambiences, a drain current on/off ratio R, is defined here as [42]:…”

“…The R reveals a decreasing trend when the hydrogen concentration is higher than 50 ppm/air. Due to the negligibly low change of I OFF under lower hydrogen concentration (<50 ppm H 2 /air), the increase in R is mainly dominated by the increase of I ON [42]. However, when the hydrogen concentration is higher than 50 ppm H 2 /air, the off current I OFF shows a remarkable increase along with the increase in hydrogen concentration [42], leading to a decrease in R. Experimentally, based on the excellent suppression of I OFF by a low-temperature EP approach, a significant improvement in the R performance of the EP Pt-gate HFET is acquired.…”

On an Integrated Gas Sensing System Based on an AlGaN/GaN Heterostructure Compound Semiconductor

“…The transient response and recovery times are defined as the times needed to reach 70% values of the subtraction between the initial and final steady-state currents under a hydrogen-containing gas and air. 25 The corresponding transient response and recovery times of device A are 3 s and 20 s upon exposing to a 1000 ppm H 2 /air gas. Figure 5b presents the transient response curve of device B at 200 • C. The applied voltage is fixed at 0.5 V. When a 1000 ppm NH 3 /air gas is introduced and removed, the response curve rises up and falls down quickly.…”