Hydrogen sensor based on thin film nanocrystalline n-GaN/Pd Schottky diode

Nanocrystalline n-GaN in thin film form was deposited onto fused silica substrates by high pressure dc sputtering of Si(1 at%) doped GaN target. An Al/n-GaN/Pd Schottky diode was realized by depositing n-GaN nanocrystalline layer onto Al-coated fused silica substrate under identical deposition conditions. Top Pd contacts were obtained by evaporating Pd using an appropriate mask. Corresponding current-voltage characteristics of the Schottky diodes were recorded before and after hydrogen gas exposure. I-V variations were analysed in the light of the existing theories. The ideality factor for the Schottky diodes varied between 3.4 and 4.5. The series resistance of the diode before gas and after gas exposure were found to be ∼500 kΩ and ∼300 kΩ, respectively. The barrier height could be seen to decrease significantly with increased hydrogen concentration while it increased with temperature