Interesting hydrogen-sensing properties of catalytic Pt/In0.5Al0.5P metal-oxide-semiconductor (MOS) and metal-semiconductor (MS) Schottky diodes are comprehensively studied and compared. The effects of hydrogen adsorption are investigated on the device performance such as the current-voltage characteristics, relative sensitivity ratio, Schottky barrier height variation, and built-in electric field. Experimentally, both the hydrogen sensors can be operated systematically under bi-polarity biases. The detecting sensitivity of the MOS-type hydrogen sensor is superior to that of the MS-type. It is believed that a high-quality oxide layer effectively increases the amount of hydrogen atoms adsorbed. Also, the hydrogen effects are found on both the Schottky barrier height lowering and the modulation in the electric field at the Pt-oxide and Pt-InAlP interfaces. In addition, the influence of the oxygen partial pressure in synthetic air and the existence of an oxygen layer between the Pt metal and the InAlP material are also studied.
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