Fluorine and related complexes in α-Al2O3

Using first-principles calculations based on hybrid-density-functional theory, we examine the energetics and electronic structure of fluorine in a-Al 2O 3. The F atom can be incorporated as an interstitial (F i) or substitutional impurity on the oxygen site (F O); the latter tends to be lower in energy, particularly under Al-rich conditions. Fluorine on the oxygen site acts as a donor, but for Fermi-level positions high in the bandgap, a negatively charged D X configuration is lower in energy. Fluorine substituting on the Al site is not energetically stable. We also examine complexes between F and hydrogen or carbon, which can easily be unintentionally incorporated during growth or processing. Our calculated defect levels, combined with band alignments, allow us to assess the impact on Al 2O (3)/semiconductor heterostructures. We find that F can passivate oxygen-vacancy related traps in the Al O-2( 3) dielectric. Complex formation with H or C is either ineffective or could even be detrimental.