RF-MBE GROWTH OF GaN ON SAPPHIRE FOR GAS SENSING APPLICATION

Besides SiC, a group III-V nitrides are also suitable large-band gap semiconductor materials for high-temperature gas sensor devices. In this paper, we present the study of the H-2 sensitive device fabricated based on n-type GaN wafer. The GaN thin film with AlN buffer layer was grown on sapphire by RF plasma-assisted molecular beam epitaxy (RF-MBE). A few monolayers of AlN were deposited using high flux Al before the growth of the AlN buffer layer. This step is speculated to be able to form a better relaxed layer for the subsequent growth of the AlN buffer layer. Pt contacts with thickness of about 150 nm were then deposited on the GaN/AlN/Al2O3 using the sputtering system. Gas detection was carried out at room temperature. Prior to the current-voltage (I-V) measurements, the samples were annealed at temperatures ranging from 200 degrees C to 600 degrees C in N-2 ambience. A significant change of current in the Pt/GaN gas sensor was observed for the 600 degrees C annealed sample when exposed to 0.5% H-2 in N-2 gas.