Theoretical study of sorption and diffusion of lithium atoms on the surface of crystalline silicon and inside it

The energy of the sorption and diffusion of lithium atoms on the reconstructed ($4 \times 2$) (100) silicon surface in the process of their transport into near-surface layers, as well as inside crystalline silicon, at various lithium concentrations have been investigated within the density functional theory. It has been shown that single lithium atoms easily migrate on the (100) surface and gradually fill the surface states (T3 and L) located in channels between silicon dimers. The diffusion of lithium into near-surface silicon layers is hampered because of high potential barriers of the transition ($1.22$ eV). The dependences of the binding energy, potential barriers, and diffusion coefficient inside silicon on distances to the nearest lithium atoms have also been examined. It has been shown that an increase in the concentration of lithium to the Li$_{0.5}$Si composition significantly reduces the transition energy (from $0.90$ to $0.36$ eV) and strongly increases (by one to three orders of magnitude) the lithium diffusion rate.