Structure and energetics of elementary defects in 4H-SiC

Silicon carbide is a promising material for applications in special electronic devices. Ion implantation is considered to be the best means to introduce dopants into SiC in a controlled manner. However, ion irradiation produces defects which can prevent the electrical activation of the implanted dopants. The understanding of ion-beam induced defect formation and evolution in SiC is therefore very important. A peculiarity of SiC is the occurence of polytypism. It can be illustrated by different stacking sequences of layers formed by SiC4 (or CSi4) tetrahedra. Wafers available for technological applications are either 4H or 6H-SiC single crystals, i.e. polytypes with hexagonal symmetry. The present work deals with structure and energetics of elementary defects in 4H-SiC. Based on the lattice structure and symmetry, a classification of potential vacancies, antisite defects and interstitials is given. In comparison with the cubic polytype 3C-SiC which was already studied in detail a considerably higher number of nonequivalent defect sites is found. The stability, formation energy, and structural details of the potential defects is investigated by classical MD simulations using a recently developed interatomic potential of Brenner type. Most of the potential defects are found to be stable. Many of them show a similar structure and formation energy. In these cases the first and the second nearest neighbor atoms of the defect site are identical.