First-principles simulations of atomic networks and optical properties of amorphousSiNxalloys

Abstract

We report ab initio generated atomic networks of amorphous silicon-nitrogen alloys, $a\ensuremath{-}{\mathrm{SiN}}_{x},$ for 13 different values of content x [from 0 to the nearly stoichiometric composition of $x=(36/28)=1.29].$ The amorphous structures were obtained using a new thermal procedure. 64-atom periodically continued cubic diamondlike cells, containing silicon and randomly substituted nitrogen, were amorphized by ``heating'' them to just below the corresponding melting temperatures, using a 6 fs time step and a Harris-functional based molecular dynamics code. After cooling, annealing, and optimizing, radial distribution functions (RDFs) and optical gaps were calculated for all samples. All the partial radial features obtained are new; the total RDF's agree very well with the scarce experimental results. The electron energy levels were then calculated and the optical gaps obtained using a novel Tauc-like procedure that is not sensitive to gap states and band tails. The gap values agree with experiment.