Hydrogen Sensors Based On Sc2o3/Algan/Gan High Electron Mobility Transistors

Pt contacted AlGaN/GaN high electron mobility transistors with Sc2O3 gate dielectrics show reversible changes in drain-source current upon exposure to H-2-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 degrees C for the HEMTs and a change in forward current of similar to 40 mu A at a bias of 2.5 V was obtained for the MOS-diodes in response to a change in ambient from pure N-2 to 10% H-2/90% N-2. The current changes in the latter case are almost linearly proportional to the testing temperature and reach around 400 mu A at 400 degrees 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 degrees C for 10%H-2 90%N-2 ambients relative to pure N-2 and is due to catalytic dissociation of the H, on the Pt contact, followed by diffusion to the Sc2O3/AlGaN interface. (c) 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weiheim.