Comprehensive study of a Pd–GaAs high electron mobility transistor (HEMT)-based hydrogen sensor

• Published in: Sensors and actuators. B, Chemical Vol. 122; no. 1; pp. 81 - 88
• Main Authors: Hung, Ching-Wen, Lin, Han-Lien, Chen, Huey-Ing, Tsai, Yan-Ying, Lai, Po-Hsien, Fu, Ssu-I, Chuang, Hung-Ming, Liu, Wen-Chau
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 08.03.2007
• Subjects: Adsorption; Channels; Devices; Equilibrium; Gallium arsenide; HEMT; High electron mobility transistors; Kinetics; Palladium; Semiconductor devices; Sensors; Palladium; Kinetics; HEMT; Equilibrium
• ISSN: 0925-4005; 1873-3077
• DOI: 10.1016/j.snb.2006.05.007

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 Al 0.24Ga 0.76As 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 H 2/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.