Nitric acid oxidation of silicon at ∼120°C to form 3.5-nm SiO2∕Si structure with good electrical characteristics

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3.5-nm-thick SiO2 layers can be formed at 120 °C by immersion of Si in 40 wt % nitric acid (HNO3) followed by immersion in an azeotropic mixture (i.e., 68 wt % HNO3). The former immersion produces a 1.1-nm SiO2 layer with a low atomic density of 2.19×1022∕cm2, where the layer acts as a catalyst for the decomposition of HNO3. The latter immersion results in a 3.5-nm SiO2 layer with a higher atomic density of 2.22×1022∕cm2. When the postmetalization annealing treatment at 250 °C in hydrogen is performed on the ⟨Al∕3.5-nmSiO2∕Si(100)⟩ metal-oxide semiconductor diodes, interface states are passivated and a low leakage current density (e.g., 8×10−4A∕cm2 at the forward gate bias of 1.5 V) is achieved.