Nitrogen adsorption phases on the 4H-SiC(0 0 0 1) Si-face

Using the density functional theory this paper identifies two phases of nitrogen which form on the 4H-SiC(0 0 0 1) Si-face. At 13 ML, N-adatoms occupy the sites between three surface silicon atoms bonding to each of the three available half-filled silicon dangling bonds. This passivates the surface dangling bonds and removes states from the upper half of the band gap. Above this coverage nitrogen atoms pair on the surface to form dimers with a corresponding change in the chemical potential. The nitrogen dimers reintroduce states into the SiC band gap. Between 13 ML and 1 ML coverage, the nitrogen redistributes in patches corresponding to regions of 13 ML coverage and 1 ML coverage. At 1 ML the nitrogen dimers populate all the silicon dangling bonds, thus forming a new surface phase. Above 1 ML a third bonding configuration appears in which the nitrogen dimers are only a singly bonded to the surface. This configuration saturates at 2 ML.