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Open-Gated pH Sensor Fabricated on an Undoped-AlGaN/GaN HEMT Structure

Material Innovations and Nanoelectronics Research Group, Faculty of Electrical Engineering, Universiti Teknologi Malaysia, 81310 Skudai, Johor, Malaysia
Department of Electronics, Kyushu University, 744 Motooka, Fukuoka 819-0395, Japan
Author to whom correspondence should be addressed.
Sensors 2011, 11(3), 3067-3077;
Received: 10 January 2011 / Revised: 28 February 2011 / Accepted: 7 March 2011 / Published: 9 March 2011
(This article belongs to the Section Chemical Sensors)
The sensing responses in aqueous solution of an open-gated pH sensor fabricated on an AlGaN/GaN high-electron-mobility-transistor (HEMT) structure are investigated. Under air-exposed ambient conditions, the open-gated undoped AlGaN/GaN HEMT only shows the presence of a linear current region. This seems to show that very low Fermi level pinning by surface states exists in the undoped AlGaN/GaN sample. In aqueous solution, typical current-voltage (I-V) characteristics with reasonably good gate controllability are observed, showing that the potential of the AlGaN surface at the open-gated area is effectively controlled via aqueous solution by the Ag/AgCl gate electrode. The open-gated undoped AlGaN/GaN HEMT structure is capable of distinguishing pH level in aqueous electrolytes and exhibits linear sensitivity, where high sensitivity of 1.9 mA/pH or 3.88 mA/mm/pH at drain-source voltage, VDS = 5 V is obtained. Due to the large leakage current where it increases with the negative gate voltage, Nernstian like sensitivity cannot be determined as commonly reported in the literature. This large leakage current may be caused by the technical factors rather than any characteristics of the devices. Surprisingly, although there are some imperfections in the device preparation and measurement, the fabricated devices work very well in distinguishing the pH levels. Suppression of current leakage by improving the device preparation is likely needed to improve the device performance. The fabricated device is expected to be suitable for pH sensing applications. View Full-Text
Keywords: AlGaN/GaN; pH sensor; open-gated structure; liquid-pHase; HEMT AlGaN/GaN; pH sensor; open-gated structure; liquid-pHase; HEMT
MDPI and ACS Style

Abidin, M.S.Z.; Hashim, A.M.; Sharifabad, M.E.; Rahman, S.F.A.; Sadoh, T. Open-Gated pH Sensor Fabricated on an Undoped-AlGaN/GaN HEMT Structure. Sensors 2011, 11, 3067-3077.

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