Temperature-dependent properties of Pd/GaN Schottky type hydrogen sensors with Cl ₂ plasma surface treatments

Temperature-dependent hydrogen sensing properties of Pd/GaN Schottky type sensors with different Cl ₂ plasma surface treated times are studied and demonstrated. The sensing behaviors are studied in terms of Schottky barrier height variation Δ _B, sensing response S _r, and transient-state response times. The highest sensing response (S _r) values of 7.1 × 10 ⁴ and 2.12 × 10 ⁵ are obtained in forward- and reverse-bias voltages, respectively, upon exposure to a 10,000 ppm H ₂/air gas at 30°C. In addition, a correspondingly large Schottky barrier height variation Δ _B of 0.38 eV is found. This could be attributed to the effective dissociation of hydrogen molecules due to a rougher Pd surface and lower baseline current. Moreover, the studied devices with Cl ₂ plasma surface treatment have a stable and widespread reverse voltage operation regime. From transient-state behaviors measurement, the studied device with a 30 s plasma surface treatment shows the overshooting phenomenon and fast response (recovery) time of 4 (5) s.