Ab initio study of boron doping in tetrahedral amorphous carbon

We present an ab initio study of the effects of boron incorporation in tetrahedral amorphous carbon using Car-Parrinello molecular dynamics. Samples of tetrahedral amorphous carbon at a density of 2.9 g/cm3 with different boron contents (1.6% and 3.2%) have been generated by quenching from the liquid phase. We found that boron is mainly threefold coordinated and does not affect the fraction of fourfold coordinated carbon atoms, in agreement with experimental findings. Moreover, boron incorporation in highly stressed three-membered rings induces the opening of the ring which might provide a possible mechanism of the stress release observed experimentally upon boron doping. An analysis of the electronic properties reveals that boron does not induce shallow acceptor levels in the gap in any of the cases studied. ©1999 The American Physical Society.