An interesting Pd-GaAs high electron mobility transistor (HEMT) hydrogen sensor is fabricated and studied. For the studied device, a 5 nm-thick undoped GaAs cap layer is grown to suppress the oxidation of the underneath Al0.24Ga0.76As layer. Comprehensive analysis on the electrical properties including equilibrium adsorption (steady-state) and kinetic adsorption (transient) is presented. Experimentally, a high current variation of 17.1 mA/mm is obtained in 9970 ppm H2/air gas at 323 K. A high channel conductance variation of 25.1 mS/mm is also found under the same conditions. This indicates that, in hydrogen-containing ambience, the channel resistance reduces in the linear region of transistor operation. The reaction enthalpy and entropy are -112.74 kJ mol-1 and -367.39 J mol-1 K-1, respectively. This interprets that the hydrogen adsorption process is exothermic and the hydrogen atoms are more ordered when they are adsorbed in a dipolar layer at the metal-semiconductor interface. In the transient analysis, the rate constants of the studied device can be calculated. Then the activation energy of about 33.09 kJ mol-1 is obtained.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Surfaces, Coatings and Films
- Metals and Alloys
- Electrical and Electronic Engineering
- Materials Chemistry