Hydrogen sensing characteristics and mechanism of Pd/AlGaN/GaN Schottky diodes subjected to oxygen gettering

Hydrogen sensing characteristics in vacuum and in air were investigated on Pd Schottky diodes that were formed on AlGaN/GaN two-dimensional electron gas wafer and subjected to a surface control process for oxygen gettering. By applying the surface control process, leakage currents in Pd/AlGaN/GaN Schottky diode were greatly reduced. Such diodes showed high hydrogen detection sensitivities and fast turn-on and -off characteristics in air, although they showed very slow turn-off behavior in vacuum. From detailed measurements of current-voltage (I-V), capacitance-voltage (C-V), and current transient characteristics, the sensing mechanism was explained in terms of Schottky barrier height reduction caused by formation of interface dipole by atomic hydrogen. It was shown that dipole formation is controlled in air by the Langmuir isotherm type adsorption behavior, including the reaction between atomic hydrogen and oxygen. Discrepancies in Schottky barrier height values deduced from I-V and C-V measurements have indicated that current transport is not by the standard thermionic emission process, but by the thermionic field emission process through the thin surface barrier (TSB) in accordance with the TSB model. (C) 2007 American Vacuum Society.