Ab initiostudy of hydrogenation effects in amorphous silicon carbide

We propose a structural model of hydrogenated amorphous silicon carbide (a-SiC:H) at stoichiometric composition and low H content, based on the results of ab initio molecular-dynamics simulations. As found for a-SiC, the system has a complex structure which cannot be described as a distorted crystalline phase. Nevertheless, the degree of chemical order is larger in the hydrogenated network than in the pure network. H binds to both C and Si. H bound to C gives rise to ${\mathit{sp}}^3$ bonded monohydrated sites, thus favoring the formation of a tetrahedral network. H bound to Si forms diverse bonding configurations where weak and strong bonds can be identified. These results are in agreement with recent experiments. Furthermore, our findings for the evolution of Si-H and C-H bonding as a function of temperature are consistent with recent measurements of H desorption from Si-C alloys. Finally, we suggest an interpretation of x-ray and neutron-diffraction data based on analyses of several total distribution functions.