Dopant-related electron trap states in Lu2O3:Ta

Abstract

Electronic structure of Ta-doped cubic (bixbyite-type) lutetium oxide was analyzed using augmented plane wave with local orbitals density functional theory (DFT) calculations with meta-generalized gradient approximation (meta-GGA, mGGA) Räsänen, Pittalis and Proetto functional. Two doping sites, three oxidation states of the dopant and optional interstitial oxygen (Oi) were considered. The calculations indicate that introduction of the dopant results in energy levels below conduction band, with strong contribution of Ta 5d orbitals. The position of the levels depends strongly on the oxidation state of the dopant. Depending on the composition, two distinct electron traps with depths of 1.5–1.2 eV and 0.9–0.2 eV were revealed. Introduction of Oi at proximity of the Ta dopant results in partial overlap of the Ta-related defect states with conduction band, which makes the traps very shallow, deteriorating the electron trapping properties. In some cases, shallow hole traps can also be attributed to the Oi. The calculated traps structure is in good accord with the experimental data.