Improved Interface and Electrical Properties by Inserting an Ultrathin SiO 2 Buffer Layer in the Al 2 O 3 /Si Heterojunction

An ultrathin SiO 2 interfacial buffer layer is formed using the nitric acid oxidation of Si (NAOS) method to improve the interface and electrical properties of Al 2 O 3 /Si, and its effect on the leakage current and interfacial states is analyzed. The leakage current density of the Al 2 O 3 /Si sample (8.1 × 10 −9 A cm −2 ) due to the formation of low‐density SiO x layer during the atomic layer deposition (ALD) process, decreases by approximately two orders of magnitude when SiO 2 buffer layer is inserted using the NAOS method (1.1 × 10 −11 A cm −2 ), and further decreases after post‐metallization annealing (PMA) (1.4 × 10 −12 A cm −2 ). Based on these results, the influence of interfacial defect states is analyzed. The equilibrium density of defect sites ( N d ) and fixed charge density ( N f ) are both reduced after NAOS and then further decreased by PMA treatment. The interface state density ( D it ) at 0.11 eV decreases about one order of magnitude from 2.5 × 10 12 to 7.3 × 10 11 atoms eV −1 cm −2 after NAOS, and to 3.0 × 10 10 atoms eV −1 cm −2 after PMA. Consequently, it is demonstrated that the high defect density of the Al 2 O 3 /Si interface is drastically reduced by fabricating ultrathin high density SiO 2 buffer layer, and the insulating properties are improved.