Hydrogen sensing performance of a Pd/HfO2/GaN metal-oxide-semiconductor (MOS) Schottky diode

Abstract

A hafnium oxide (HfO2) layer, prepared using a sputtering approach, is employed to produce a Pd/HfO2/GaN-based metal-oxide-semiconductor (MOS)-type Schottky diode. The hydrogen sensing characteristics of this MOS diode are comprehensively studied. Experimentally, upon exposure to 1% H2/air gas at 300 K, the studied device shows a higher sensing response of 4.9 × 105 (139) under an applied forward- (reverse-) voltage of 0.5 V(–2 V). A lower detection limit of 5 ppm H2/air is obtained. Reversible, high-speed sensing properties are found at higher operating temperatures. The response (recovery) time constant is decreased from 39 s (42 s) to 5.3 s (2.5 s) when the temperature is increased from 300 to 383 K. The humidity effect and hydrogen adsorption mechanism at the Pd/HfO2 interface are also studied in this work. The exothermic action of the hydrogen adsorption process leads to a decreased hydrogen sensing response at higher temperatures. Consequently, the studied Pd/HfO2/GaN MOS diode is promising for high-performance hydrogen sensing applications and integration with other GaN-based high-speed devices on a chip.