Energy-band alignment of atomic layer deposited (HfO2)x(Al2O3)1 − x gate dielectrics on 4H-SiC**Project supported by the National Natural Science Foundation of China (Grant Nos. 51272202 and 61234006) and the Science Project of State Grid, China (Grant No. SGRI-WD-71-14-004).

Abstract

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 eV and the conduction band offset of HfAlO is 1.11–1.72 eV. The conduction band offsets of (HfO2)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 eV) for both electrons and holes. With a higher conduction band offset, (HfO2)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-SiC power MOS-based transistors.