Hydrogen surface passivation of Si and Ge nanowires: A semiempirical approach

A semiempirical nearest-neighbor tight-binding approach, that reproduces the indirect band gaps of elemental semiconductors, has been applied to study the electronic and optical properties of Si and Ge nanowires (NWs). The calculations show that Si-NWs keep the indirect bandgap whereas Ge-NWs changes into the direct bandgap when the wire cross section becomes smaller. Also, the band gap enhancement of Si-NWs showing to quantum confinement effects is generally larger than that of similar-sized Ge-NWs, confirming the larger quantum confinement effects in Si than in Ge when they are confined in two dimensions. Finally, the dependence of the imaginary part of the dielectric function on the quantum confinement within two different schemes: intra-atomic and interatomic optical matrix elements are applied.