Investigation on a Pd–AlGaN/GaN Schottky Diode-Type Hydrogen Sensor With Ultrahigh Sensing Responses

Abstract

An interesting Pd-AlGaN/GaN Schottky diode-type hydrogen sensor with ultrahigh sensing responses is fabricated and studied. A sensing response (S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">F</sub> ) of 2.04 times 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> and a widespread Schottky barrier height variation (Deltaphi <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</sub> ) of 400 meV are observed upon exposure to a 9660 ppm H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /air gas at 150degC. The high sensing response can be attributed to the catalytic capability of Pd metal with contributions from a high-density 2-D electron gas induced from spontaneous and piezoelectric polarizations. From a Langmuir isotherm, the equilibrium constants are found to be 1.9 and 0.7 torr <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> at 150degC and 200degC, respectively. The fast response and recovery times (< 10 s) are found under a 9660 ppm H <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> /air gas. Consequently, the compatible process of the AlGaN/GaN sensor makes it possible to be integrated into other high-sensing performance sensor for microelectrical and mechanical applications.