Aluminum-based high-k dielectric materials have been studied for their potential use as passivation for SiC devices. Metal-insulator-semiconductor structures were prepared and their dielectric properties were analyzed using capacitance-voltage and current-voltage measurements. Atomic layer deposition was used for the deposition of dielectric layers consisting of AlN with or without a buffer layer of SiO2, and also a stack of alternating AlN and Al2O3 layers. It has been observed that AlN has a polycrystalline structure which provides leakage paths for the current through the grain boundaries. However, adding alternate amorphous layers of Al2O3 prevent this leakage and give better overall dielectric properties. It is also concluded that the breakdown of the dielectric starts from the degradation of the thin interfacial SiO2 layer.