First-principles calculations of the electrical properties ofLaAlO3and its interface with Si

Abstract

$\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ is one of the potential candidates to replace $\mathrm{Si}{\mathrm{O}}_{2}$ as a high permittivity dielectric for future generations of metal-oxide-semiconductor field effect transistors. Using first-principles plane-wave calculations within density functional theory, its bulk and surface electronic properties and the relative stability of cubic $c\text{\ensuremath{-}}\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}(001)∕\mathrm{Si}(001)$ interfaces are investigated. In agreement with experiment, our study shows that the dielectric constant of crystalline $\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}$ $(\ensuremath{\sim}30)$ is comparable to that of hexagonal ${\mathrm{La}}_{2}{\mathrm{O}}_{3}$. To accurately calculate the $c\text{\ensuremath{-}}\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}(001)$ surface energy, several ways of eliminating the surface dipole moment of the polar surface are presented, with the transfer of an oxygen anion from one boundary surface to the other being identified as the energetically most favorable mechanism. We have found that lanthanum-terminated $c\text{\ensuremath{-}}\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}(001)∕\mathrm{Si}(001)$ interfaces are in general more stable than aluminum-terminated interfaces for both the oxidized and nonoxidized Si(001) surfaces. We have also identified a significant reduction of the $c\text{\ensuremath{-}}\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}(001)∕\mathrm{Si}(001)$ valence band offset due to the creation of interface dipoles for O-rich interfaces. Analysis of the density of interface states shows that La-Si bonds at the $c\text{\ensuremath{-}}\mathrm{La}\mathrm{Al}{\mathrm{O}}_{3}(001)∕\mathrm{Si}(001)$ interface do not create interface states in the silicon band gap, in contrast to Hf-Si bonds in $m\text{\ensuremath{-}}\mathrm{Hf}{\mathrm{O}}_{2}(001)∕\mathrm{Si}(001)$ interfaces studied previously.