First-principles investigation of the atomic and electronic structure of the4H-SiC(11¯02)−c(2×2)surface

Abstract

We present results of a comprehensive ab initio investigation of the atomic and electronic structure of a variety of reconstruction models for the $4H\text{-SiC}(1\overline{1}02)\text{\ensuremath{-}}c(2\ifmmode\times\else\texttimes\fi{}2)$ surface. The basic structural building blocks are Si adatoms residing in $H3$ or $T4$ sites above the surface and carbon dimers in the top layer, respectively. These reduce the number of surface dangling bonds per unit cell from twelve at the ideal surface to only two in the different reconstruction models investigated. Several arrangements of triple-bonded carbon dimers bridging two second-layer Si atoms or double-bonded carbon dimers are considered. A configuration with double-bonded carbon dimer pairs and Si adatoms in $H3$ sites turns out to be most favorable. It is 2.1 eV per unit cell lower in total energy than the reconstruction model suggested earlier solely on the basis of experimental data. A reaction pathway of the surface from an initial configuration with Si adatoms in metastable $T4$ sites to the final adsorption configuration with Si adatoms in the most stable $H3$ sites is investigated, revealing an energy barrier of about 0.4 eV between the two. The electronic structure of several reconstruction models is analyzed by calculated surface band structures, charge-density distributions, and scanning tunneling microscopy images. The results are discussed in comparison with most recent experimental data.