Unidirectional sensing characteristics of structured Au-GaN-Pt diodes for differential-pair hydrogen sensors

A new metal-semiconductor-metal (MSM) hydrogen sensor was proposed to avoid (or to reduce) false alarms due to temperature drift when it is used in differential-pair hydrogen-sensing systems. A GaN semiconductor layer together with Pt as catalytic metal and Au as Schottky metal was employed to structure an Au-GaN-Pt MSM sensor. In particular, the structured Au-GaN-Pt MSM sensor can function as an active sensor and a reference sensor, depending on the polarity of applied voltage, in a differential-pair sensing circuit. Possible sensing mechanisms associated with the Au-GaN-Pt MSM sensor were described first to include band diagrams and graphical analysis. Experimental results reveal that an active sensor by forward-biasing the Au-GaN-Pt MSM sensor responses well to hydrogen-containing gases (50, 500, and 5000 ppm H-2/N-2) at various temperatures (25 degrees C, 50 degrees C, 70 degrees C, and 90 degrees C). High sensing current gains over 10(4) were obtained. Further, the Au-GaN-Pt MSM sensor can also be reverse-biased to act as a reference sensor which shows negligible responses to hydrogen-containing gases. The differential-pair sensing circuit with the proposed Au-GaN-Pt MSM sensor reduces false alarms due to ambient temperature variation while it provides a short detection time. Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.