Investigation of Leakage Current Mechanisms in La₂O₃/SiO₂/4H-SiC MOS Capacitors with Varied SiO₂ Thickness

Abstract

In this study, the material and electrical properties of La₂O₃/SiO₂/4H-SiC metal–oxide–semiconductor (MOS) capacitors are systematically characterized. Thermal oxidization SiO₂ with varying thickness (0 nm, 3.36 nm, 5 nm, 8 nm, and 30 nm) were coated with La₂O₃ using atomic layer deposition on n-type 4H-SiC. The stacking oxides were measured using atomic force microscopy, transmission electron microscopy, and x-ray photoelectron spectroscopy, and the MOS capacitors were measured by capacitance–voltage and current–voltage measurements. The results demonstrate that the main gate current leakage mechanisms are dependent on the thickness of the SiO₂ oxide under the applied electric field. The primary mechanism for current leakage from the La₂O₃/4H-SiC MOS capacitor follows the Schottky emission mechanism due to its low conduction band offset. In contrast, the current leakage mechanism for the capacitor with a 3.36 nm SiO₂ layer follows the Poole–Frenkel emission mechanism on account of its high trap charge density in the gate dielectric and at the interface. When the thickness of the SiO₂ layer increases to 8 nm, lower leakage current is observed by reason of the low trap charge density and high conduction band offset when E ≤ 5 MV/cm. As the electric field strength increases to 5 MV/cm and 5.88 MV/cm (30 nm SiO₂: 4.8 MV/cm), the main current leakage mechanism changes to the Fowler–Nordheim tunneling mechanism, which indicates that the La₂O₃/SiO₂ stacking structure can improve the properties of MOS capacitors.