First-principles study of hydrogenated amorphous silicon

Abstract

We use a molecular-dynamics simulation within density-functional theory to prepare realistic structures of hydrogenated amorphous silicon. The procedure consists of heating a crystalline structure of ${\text{Si}}_{64}{\text{H}}_{8}$ to 2370 K, creating a liquid and subsequently cooling it down to room temperature. The effect of the cooling rate is examined. We prepared a total of five structures which compare well to experimental data obtained by neutron-scattering experiments. Two structures do not contain any structural nor electronic defects. The other samples contain a small number of defects which are identified as dangling and floating bonds. Calculations on a bigger sample $({\text{Si}}_{216}{\text{H}}_{27})$ show similar properties (radial distribution functions, band gap, and tail states) compared to the ${\text{Si}}_{64}{\text{H}}_{8}$ sample. Finally the vibrational density of states is calculated and compared to inelastic neutron-scattering measurements.