Properties of Bilayer Zr- and Sm-Oxide Gate Dielectric on 4H-SiC Substrate Under Varying Nitrogen and Oxygen Concentrations

This work systematically analyses the electrical and structural properties of a bilayer gate dielectric composed of Sm2O3 and ZrO2 on a 4H-SiC substrate. The bilayer thin film was fabricated using a sputtering process, followed by a dry oxidation step with an adjusted oxygen-to-nitrogen (O2:N2) gas concentration ratio. XRD analysis validated formation of an amorphous structure with a monoclinic phase for both Sm2O3 and ZrO2 dielectric thin films. High-resolution transmission emission (HRTEM) analysis verified the cross-section of fabricated stacking layers, confirmed physical oxide thickness around 12.08–13.35 nm, and validated the amorphous structure. Meanwhile, XPS confirmed the presence of more stoichiometric dielectric oxide formation for oxidized/nitrided O2:N2-incorporated samples, and more sub-stochiometric thin films for samples only oxidized in ambient O2. The oxidation/nitridation processes with N2 incorporation influenced the band offsets and revealed conduction band offsets (CBOs) ranging from 2.24 to 2.79 eV. The affected charge movement and influenced electrical performance where optimized samples with gas concentration ratio of 90% O2:10% N2 achieved the highest electrical breakdown field of 10.1 MV cm−1 at a leakage current density of 10−6 A cm−2. This gate stack also improved key parameters such as the effective dielectric constant (keff) up to 29.75, effective oxide charge (Qeff), average interface trap density (Dit), and slow trap density (STD). The bilayer gate stack of Sm2O3 and ZrO2 revealed potential attractive characteristics as a candidate for high-k gate dielectric applications in metal-oxide-semiconductor (MOS)-based devices.