Ab initio study of boron doping in tetrahedral amorphous carbon

We present an ab initio study of the effects of boron incorporation in tetr ahedral amorphous carbon using Car-Parrinello molecular dynamics. Samples o f tetrahedral amorphous carbon at a density of 2.9 g/cm(3) with different b oron contents (1.6% and 3.2%) have been generated by quenching from the liq uid phase. We found that boron is mainly threefold coordinated and does not affect the fraction of fourfold coordinated carbon atoms, in agreement wit h experimental findings. Moreover, boron incorporation in highly stressed t hree-membered rings induces the openings 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 n ot induce shallow acceptor levels in the gap in any of the cases studied. [ S0163-1829(99)03338-X].