Control of Oxygen Vacancies in TiO6 Octahedra of Amorphous BaTiO3 Thin Films with Tunable Built‐In Electric Field in a‐BaTiO3/p‐Si Heterojunction for Metal–Oxide–Semiconductor Applications

Abstract

Amorphous BaTiO3 (a‐BTO) thin films are deposited on p‐Si(111) substrates by radio frequency (RF) magnetron sputtering without extra substrate heating. The microstructure of a‐BTO thin films is modified by postannealing at low temperatures (260–600 °C) in air. The results show that distorted TiO6 octahedra exist in a‐BTO thin films, and the degree of distortion decreases when the annealing temperature rises. The concentration of O vacancies in the TiO6 of the thin films remains high when postannealed between 370 and 460 °C, and a built‐in electric field across the a‐BTO/p‐Si heterojunction is established in this annealing temperature range. This built‐in electric field is regulated by controlling the concentration of O vacancies from the TiO6. The tunable C–V characteristic of the Au/a‐BTO/p‐Si metal–oxide–semiconductor (MOS) capacitor is obtained by modulating the built‐in electric field at the heterojunction, and the flat band voltage of the MOS capacitor shifts from about −3 V to at least −13 V when the postannealing temperature increases from 260 to 420 °C. This kind of tunable built‐in electric field at the a‐BTO/p‐Si heterojunction, controlled by modifying the microstructure of amorphous oxide thin films, has never been observed before, which will be useful for MOS applications.