Reconstructions of the AlN(0001) surface

Abstract

Reconstructions of the AlN(0001) surface are studied. For moderately Al-rich surfaces, surface reconstructions with symmetry of $2\sqrt{3}\ifmmode\times\else\texttimes\fi{}2\sqrt{3}\ensuremath{-}R30\ifmmode^\circ\else\textdegree\fi{}$ and $5\sqrt{3}\ifmmode\times\else\texttimes\fi{}5\sqrt{3}\ensuremath{-}R30\ifmmode^\circ\else\textdegree\fi{}$ are found on the basis of scanning tunneling microscopy and low-energy electron diffraction observations. Such surfaces display a predominantly $2\ifmmode\times\else\texttimes\fi{}6$ pattern in reflection high-energy electron diffraction. Auger electron spectroscopy indicates an Al coverage for such surfaces of 2--3 monolayers. Based on this result and on first-principles total energy calculations it is argued that these reconstructions involve a laterally contracted Al adlayer structure similar to that previously proposed for GaN(0001). At higher Al coverages a thick, flat Al film is found to form on the surface. For Al-poor conditions, additional surface reconstructions with $\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\ensuremath{-}R30\ifmmode^\circ\else\textdegree\fi{}$ and $2\ifmmode\times\else\texttimes\fi{}2$ periodicities are observed.