Improved hydrogen detection sensitivity in N-polar GaN Schottky diodes

Pt/GaN Schottky diodes fabricated on m-plane (N-polar) layers grown on sapphire exhibit much larger responses to dilute concentrations (4% in N2⁠) of hydrogen at room temperature than comparable Ga-polar devices. This is consistent with previous density functional theory indicating a very high affinity of hydrogen for the N-face surface of GaN. The rectifying current-voltage characteristics of N-face diodes make a transition to more Ohmic-like behavior after hydrogen exposure, leading to very large (∼106) maximum percentage changes in current relative to Ga-face (∼10%) or AlGaN/GaN heterostructure diodes (∼170%)⁠. The strong affinity of the N face of GaN for hydrogen also leads to a slower recovery of these diodes when hydrogen is removed from the ambient.