Role of Intrinsic Electron Trapping in Negative Charging of Amorphous Alumina

ABSTRACT Negative charging of amorphous alumina (a‐) films is important for many applications, but its nature is not yet fully understood. We investigate whether intrinsic electron traps in a‐ can contribute to film charging before and after high‐temperature anneal. Amorphous and partially crystallized alumina models are created using the melt‐quench approach. Analysis of a large set of models covering a wide range of film densities using hybrid density functional theory shows both spontaneous and activated trapping of electrons in a‐. Spontaneous trapping is found to be more prominent in high‐density, partly crystallized, models. Two types of traps are found: single‐center traps and two‐center traps. In the single‐center case, electrons localize on five‐coordinated Al ions in tetragonal pyramid coordination. Two‐center traps have electron states shared between close Al‐Al pairs. The optical ionization energies of these traps are in the range of 1–4 eV. We discuss these findings in the context of exhaustive photo‐depopulation spectroscopy (EPDS) measurements of trapped electrons in as‐deposited and partially crystallized a‐ films.