Highly sensitive nonpolar a-plane GaN based hydrogen diode sensor with textured active area using photo-chemical etching

Abstract

In this work, a highly sensitive a-plane (112¯0) GaN (a-GaN) based hydrogen sensor with a large active surface area on the Schottky contact region was fabricated and characterized. By using a simple photochemical etching technique, a striated surface morphology with triangular prisms consisting of m-plane facets on the a-GaN surface was obtained. The maximum relative current change of the etched a-GaN diode was as high as 3.8×107%, and the reduction of the effective Schottky barrier height was 0.49eV upon 4% hydrogen exposure. The photo-chemically etched a-GaN sensor showed a remarkably improved hydrogen response and good repeatability for cyclic exposure to hydrogen. The photo-chemically textured GaN surface with enlarged surface area increased the number of adsorption sites available for hydrogen molecules to catalytically-decompose into surface atoms, lowering the effective Schottky barrier height, thereby increasing the measured current. Furthermore, the hydrogen sensing properties of the etched a-GaN diodes at different values of humidity and temperature were investigated.