Impact of post-deposition annealing on the electronic properties of Al2O3/GaN interface by first-principles study

The electronic properties of Al2O3/GaN interface are investigated by first-principles calculations to explore the effects of post-deposition annealing (PDA) in O2 or N2 ambient. It is found that for the initial Al2O3/GaN interface without post-annealing, there are traps with a wide energy range in the GaN band gap, mainly caused by dangling bonds (DBs) of Ga, Al, and N atoms. However, with proper PDA in O2 ambient, the trap states induced by Al DBs completely merge into GaN conduction band, while the trap states induced by Ga DBs and N DBs completely merge into GaN valence band. Therefore, the interface shows a cleaner band structure. Nevertheless, excessive interface O content can lead to trap states around the valence band maximum induced by N DBs and O DBs. For PDA in N2 ambient, the trap states induced by Al DBs and Ga DBs can be completely suppressed under appropriate interface N content. Unfortunately, deep and shallow traps caused by N DBs can be introduced in the GaN band gap. This study systematically reveals the physical mechanism by which PDA in O2 ambient compared to N2 can significantly reduce the interface state density and improve threshold voltage stability of the device.