Comparison of Pt/GaN and Pt/4H-SiC gas sensors

The characteristics of Pt/GaN and Pt/4H-SiC Schottky diodes as gas sensors were measured as a function of temperature and ambient. Both types of diode rectifiers show rapid (<1 s) changes in forward current upon introduction of different gases (N₂, air, H₂, CF₄) into the ambient. The diodes can be operated at large forward currents, leading to large signal sizes for switching from one gas ambient to another. For GaN, a shift of ∼0.2 V at 25 °C and ∼0.7 V at 150 °C was obtained at a fixed forward current for switching from N₂ to 10% H₂ in N₂. For SiC, under similar conditions, shift of 1.34 V at 25 °C was obtained at a fixed forward current of 0.2 A for switching from N₂ to 10% H₂ in N₂. The signal size increases with increasing measurement temperature due to more efficient cracking of the gas molecules. Both types of devices appear well suited to combustion control and leak detection.