Nitric acid oxidation method to form SiO2/3C–SiC structure at 120 °C

3C–SiC(0 0 1) surfaces are considerably rough with the roughness root mean square value (Rms) of 1.3 nm, but the surfaces become considerably smooth (i.e., Rms of 0.5 nm) by heat treatment in pure hydrogen at 400 °C. Two-step nitric acid (HNO3) oxidation (i.e., immersion in ∼40 wt% HNO3 followed by that in 68 wt% HNO3) performed after the hydrogen treatment can oxidize 3C–SiC at extremely low temperature of ∼120 °C, forming thick SiO2 (e.g., 21 nm) layers. With no hydrogen treatment, the leakage current density of the 〈Al/SiO2/3C–SiC〉 metal-oxide-semiconductor (MOS) diodes is high, while that for the MOS diodes with the hydrogen treatment is considerably low (e.g., ∼10−6 A/cm2 at the forward gate bias of 1 V) due to the formation of uniform thickness SiO2 layers. The MOS diodes with the hydrogen treatment show capacitance–voltage curves with accumulation, depletion, and deep-depletion characteristics.