Although tantalum pentoxide (Ta₂O₅) has been studied, both experimentally and theoretically, over the past three decades, its real emergence as a dielectric material that can be integrated with conventional CMOS has happened only in the last decade. While interest in high dielectric constant materials, in general, is primarily due to a need to scale down device sizes, the renewed interest in Ta₂O₅ is due to the ability to deposit it using conventional methods compatible with equipment and processes already available in the semiconductor industry. Nevertheless, concerns exist with Ta₂O₅ (and other alternative dielectric materials), one of them being defect densities, and their impact on the leakage currents (via defect or trap levels created in the band gap of the dielectric).

The present work attempts to theoretically characterize oxygen vacancy defects in Ta₂O₅. The atomistic structure of Ta₂O₅ was chosen so that it is computationally tractable, while at the same time is representative of deposited films. Several types of O vacancies with qualitatively different types of coordination environments were considered within this model, and the defect or trap levels due to these defects were determined using total energy calculations. Correlations between the coordination environment and the location of the defect levels will be drawn. The stability of variously charged vacancies was also considered, as a function of the vacancy type and the local chemical potential. All calculations to be presented were performed using the density functional theory, within the local density approximation, and ultrasoft pseudopotentials.