Semiempirical supercell approach to calculate the electronic and optical properties of Si quantum wires

Energy band gap and optical absorption of [001] oriented Si nanowires with diverse square cross-sections are calculated by using the sp³s* semi-empirical tight-binding (TB) model with a supercell approach. Each surface dangling bond is saturated with a hydrogen atom. The results of the variation band gap are compared with those obtained by TB-sp³d ⁵s*, the density functional theory, and experimental data in agreement with the quantum confinement scheme. The imaginary part of the dielectric function is calculated by using the interconnected and free standing (without interconnection) models for the Si skeleton. This microscopic supercell model predicts the low frequency tail in the absorption spectrum, which appears even without the allowance for the indirect optical transitions.