We study a series of(HfO2)x(Al2O3)1-x /4H-SiC MOS capacitors. It is shown that the conduction band offset of HfO2 is 0.5 e V and the conduction band offset of Hf AlO is 1.11–1.72 e V. The conduction band offsets of(Hf O2)x(Al2O3)1-x are increased with the increase of the Al composition, and the(HfO2)x(Al2O3)1-x offer acceptable barrier heights(> 1 e V)for both electrons and holes. With a higher conduction band offset,(Hf O2)x(Al2O3)1-x/4H-SiC MOS capacitors result in a ～ 3 orders of magnitude lower gate leakage current at an effective electric field of 15 MV/cm and roughly the same effective breakdown field of ～ 25 MV/cm compared to HfO2. Considering the tradeoff among the band gap, the band offset, and the dielectric constant, we conclude that the optimum Al2O3 concentration is about 30% for an alternative gate dielectric in 4H-Si C power MOS-based transistors.
The effect of the different re-oxidation annealing(ROA) processes on the SiO2/SiC interface characteristics has been investigated. With different annealing processes, the flat band voltage, effective dielectric charge density and interface trap density are obtained from the capacitance–voltage curves. It is found that the lowest interface trap density is obtained by the wet-oxidation annealing process at 1050 C for 30 min, while a large number of effective dielectric charges are generated. The components at the SiO2/SiC interface are analyzed by X-ray photoelectron spectroscopy(XPS) testing. It is found that the effective dielectric charges are generated due to the existence of the C and H atoms in the wet-oxidation annealing process.
