Stability, reconstruction, and surface electronic states of group-III atoms on SiC(111)

Abstract

The adsorption of 1/3 monolayer of the group-III elements B, Al, Ga, and In on a Si-terminated $\mathrm{SiC}(111)\sqrt{3}\ifmmode\times\else\texttimes\fi{}\sqrt{3}\mathrm{R}30\ifmmode^\circ\else\textdegree\fi{}$ surface is investigated in dependence on the surface preparation conditions using the density functional theory (DFT). The energetics, the bonding behavior and the resulting surface electronic structure are studied and chemical trends are derived. For the metal atoms Al, Ga, and In the replacement of a Si atom in a ${T}_{4}$ position always gives the most stable configuration. The first-row element B shows a completely different behavior. Under Si-rich conditions boron replaces a second-layer C atom in a ${S}_{5}$ position, whereas under C-rich conditions a first-layer Si atom is replaced by boron. The different adsorbate configurations result in completely different surface electronic structures. Al, Ga, and In adsorption passivates the surface. The fundamental gap is virtually free from empty or occupied surface states. The B adsorption in the ${S}_{5}$ configuration follows this behavior. However, boron substituting a Si-atom gives rise to an empty midgap surface band.