GaN Sensors with Metal-Oxide Mixture for Sensing Hydrogen-Containing Gases of Ultralow Concentration

The roles of micro-metal-oxide (MO) interfaces inside a sensing metal formed by coevaporating Pd and SiO2 in metal-semiconductor-metal GaN sensors are investigated. The porous property of the Pd and SiO2 mixture together with the presence of micro-MO interfaces gives rise to a highly efficient dissociation of hydrogen molecules and hence an enhanced barrier height variation (Delta phi(B)) of a reverse-biased Schottky diode. The measured Delta phi(B) increases from 294 to 392mV at a concentration coefficient of 25mV/decade as the hydrogen concentration increases from 2.13 to 10100ppm H-2/N-2. Therefore, when the sensor is subjected to 0.02 ppm H-2/N-2, Delta phi(B) as high as 245 mV is still expected. The sensor in a 2.13 ppm H-2/N-2 ambience has a sensing response of 8.7 x 10(4). Excellent dynamic responses are demonstrated by switching voltage polarity or continuously changing hydrogen concentration, showing that the proposed structure is a promising hydrogen sensor. (c) 2009 The Japan Society of Applied Physics