Atomic structure and diffusion in amorphous Si-B-C-N by molecular dynamics simulation

We carried out molecular dynamics simulation of amorphous silicon nitride containing boron and carbon, in order to investigate the short-range atomic arrangement and diffusion behavior. In amorphous Si-B-N, boron atoms are in a nearly threefold coordinated state with nitrogen atoms, while boron atoms in amorphous Si-B-C-N have bonding with both carbon and nitrogen atoms. Carbon atoms in Si-B-C-N are also bonded to silicon atoms. The self-diffusion constant of nitrogen in Si-B-N becomes much smaller than that in amorphous Si₃N₄. Also, amorphous Si-B-C-N exhibits smaller self-diffusion constants of constituent atoms, even compared to Si-B-N. Addition of boron and carbon is important in decreasing atomic mobility in amorphous Si-B-C-N. This may explain the increased thermal stability of the amorphous state observed experimentally.