Ab initio calculation of silicon monovacancy defect in amorphous-SiO2/Si interface

Defects significantly influence the electrical properties of semiconductors and their interfaces. The migration barriers and electrical properties of silicon monovacancy defect in an amorphous-SiO2/Si (a-SiO2/Si) interface are studied in this work. The minimum energy path and kinetics of monovacancy defect in the a-SiO2/Si interface are calculated by the climbing image nudged elastic band method. It is indicated that the a-SiO2/Si interface may be an effective sink for the monovacancies from the Si sublayers due to the unevenly distributed strain; the vacancy defect migrated into a-SiO2/Si interface can trigger structural changes by local distortion. The partial charge density of a monovacancy in the a-SiO2/Si interface shows that the induced defect level is localized around the unpaired Si dangling bonds and extends along the [110] zigzag chains of Si atoms. In addition, the formation energies of a silicon vacancy defect in the a-SiO2/Si interface are calculated with sophisticated corrections applicable to the interface system by combining the density functional theory calculation and finite element simulation. It is suggested that a Si monovacancy can appear in V0, V−, and V2−, and the (−/2−) and (0/−) transition levels lie at 0.15 and 0.2 eV below the CBMSi, respectively. The vacancies generated by displacement damage result in anisotropic migration and charge build-up in the a-SiO2/Si interface; for further dynamics, the ionization radiation can induce cascade reactions of displacement defects by synergistic effect between ionization and displacement radiation damages, and consequently excess base current and gain degradation in transistors.