Hydrogen influence on electrical properties of Pt-contacted α-Ga2O3/ϵ-Ga2O3 structures grown on patterned sapphire substrates

Abstract

Here we report on the influence of various gases on electrical properties of Pt-contacted α-Ga2O3 and α-Ga2O3/ϵ-Ga2O3 structures produced by halide vapor phase epitaxy on planar and patterned sapphire substrates. Pt-contacted α-Ga2O3 structures were highly resistive and exhibited no sensitivity to H2 and other gases. In contrast, α-Ga2O3/ϵ-Ga2O3 structures grown under the same conditions on patterned sapphire substrates exhibited clear and reversible response to H2. The response to H2 was thoroughly investigated at temperatures ranging from 25 °C to 200 °C and at applied biases from 1.5 V to 150 V. The lowest detectable limit of H2 at 125 °C was found to be 54 ppm. Selectivity of Ga2O3 structures against O2, NH3, СО, СН4, and H2O was examined at 125 °C and 200 °C. The structures showed little or no sensitivity to other gases at bias voltages below 7.5 V. Electrical and hydrogen sensing properties of these structures can be explained by a model of two back-to-back connected Schottky diodes which is widely used to describe metal-semiconductor-metal structures. Catalytically active Pt electrodes play an essential role in hydrogen sensing mechanism as they promote dissociation of hydrogen molecules. Accumulation of hydrogen atoms at Pt/ϵ-Ga2O3 interface results in the reduction of the Schottky energy barrier and current increase.