Origin and Structure of the First Sharp Diffraction Peak of Amorphous Silicon*

Based on a systematic study of the structure of the First Sharp Diffraction Peak (FSDP) on the structure factor at wave vector space of the continuous random network (CRN) models of amorphous silicon, we found a significant contribution to the intensity and position of the FSDP appears from the atomic correlations from radial distances up to 15 Å. Analysis of the radial shell-by-shell contribution to the FSDP revels the FSDP primarily depends on the atomic pair correlations associated with the second and fourth radial shells, with some background corrections from the first radial shell and minor perturbative corrections from the rest of the radial shells. Likewise, the numerical calculations suggest an approximate functional relation between the position (Q₀) of the FSDP and the average radial distance of the Si atoms in the second radial shell, as Q₀ is inversely proportional to the cubic power of the average radial distance of the atoms at the second radial shell of the amorphous network.