Optical properties of amorphous and crystalline silicon surfaces functionalized with Ag_n adsorbates

摘要

Light absorption by nanostructured surfaces of silicon, relevant to the capture of solar radiation, has been modeled starting from their atomic structure and calculating electronically excited states. Thin, two-layer silicon slabs were cut from a model optimized amorphous supercell and studied to elucidate the effect of adsorbate geometry and size for small silver clusters chemisorbed onto the hydrogen-passivated semiconductor surface. Density functional (DFT) and time-dependent DFT (TD-DFT) methods were performed to calculate optical properties of the amorphous Ag_n/a-Si surface. Optimized geometries, density of states, band gap and binding energies, and excited-stated spectra and oscillator strengths have been calculated within the DFT and TD-DFT approaches. The results demonstrate the correlation between these properties and the size of the systems, and are compared with those we previously obtained for the corresponding crystalline Agn/Si(111) surfaces. Similar trends are observed for the amorphous and crystalline silicon slabs as the number of silver atoms included in the clusters were increased. Our results demonstrate that Agn clusters adsorbed on amorphous slabs are significant contributors to increased light absorption of lower energy photons.