Modelling amorphous silicon with hydrogenated defects: GW treatment of the ST12 phase

The ST12 phase of silicon is investigated as a possible model for amorphous silicon (a-Si). The structure is studied both with and without hydrogenated hole defects to model the properties of hydrogenated amorphous silicon (a-Si:H) as well as a-Si. A density functional theory model of ST12 Si is structurally relaxed, and the radial correlation function and phonon density of states are used to compare the structural properties of the model to those of a-Si. One-shot GW self-energy corrections are used to generate the band structure, and the corrected electronic structure is found to reproduce the experimental energy gap of a-Si. Introducing hydrogenated defects to the ST12 structure leads to a slight decrease in the band gap and a shift in the density of states, as the breaking of symmetry results in band splitting. The dielectric functions are calculated for both a-Si and a-Si:H, using the GW corrected band structures, with a density functional perturbation theory approach. The model ST12 Si is found to absorb strongly at slightly lower energies than experimental a-Si, whereas the spectrum of the hydrogenated ST12 closely matches that of a-Si:H.