Hydrogen sensors based on Sc 2 O 3 /AlGaN/GaN high electron mobility transistors

Abstract

Pt contacted AlGaN/GaN high electron mobility transistors with Sc2O3 gate dielectrics show reversible changes in drain-source current upon exposure to H2-containing ambients, even at room temperature. The changes in current (as high as 3 mA for relatively low gate voltage and drain-source voltage at 25 °C for the HEMTs and a change in forward current of ∼40 µA at a bias of 2.5 V was obtained for the MOS-diodes in response to a change in ambient from pure N2 to 10% H2/90% N2. The current changes in the latter case are almost linearly proportional to the testing temperature and reach around 400 µA at 400 °C. These signals are approximately an order of magnitude larger than for Pt /GaN Schottky diodes and a factor of 5 larger than Sc2O3/AlGaN/GaN metal-oxide semiconductor (MOS) diodes exposed under the same conditions. This shows the advantage of using a transistor structure in which the gain produces larger current changes upon exposure to hydrogen-containing ambients. The increase in current is the result of a decrease in effective barrier height of the MOS gate of 30-50 mV at 25 °C for 10%H2/90%N2 ambients relative to pure N2 and is due to catalytic dissociation of the H2 on the Pt contact, followed by diffusion to the Sc2O3/AlGaN interface. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)