Towards aluminum oxide/aluminum nitride insulating stacks on 4H-SiC by atomic layer deposition

Stacked aluminum oxide/aluminum nitride (Al2O3/AlN) layers were deposited on n-type (0001) 4H-SiC by atomic layer deposition (ALD) processes. The structural and chemical properties have been investigated and are consistent with the growth of similar to 9 nm oriented (0001) AlN layer, and an upper 20 nm amorphous Al2O3 layer. The entire Al2O3/AlN stack was electrically characterized and compared with respect to a single Al2O3 layer having the same total thickness. The Al2O3/AlN bilayer exhibited a higher dielectric constant (kappa = 8.7), a significant reduction of the oxide trapped charges (N-OT) from 7.8 x 10(12) to 1.8 x 10(12) cm(-2), as well as a decrease of a factor 2 of the interface traps density (D-it) compared with the Al2O3 single layer values. A large positive flat band voltage shift was observed in the C-V curves acquired on MIS capacitors. The comparison of the behaviour of MIS capacitors fabricated on both n-type and p-type 4H-SiC demonstrated that deep interface states (near the 4H-SiC mid gap) acting as acceptors or donors for the n-type and p-type MIS contribute to the observed behavior. This hypothesis has been also corroborated by TCAD simulations.