Orientation effects in the electronic and optical properties of germanium quantum wires

We have performed first-principles calculations in order to analyze the influence of spatial orientation on the electronic band structure and optical properties of hydrogenated germanium quantum wires. A quantum confinement-induced direct band gap appears for the (110)-oriented wires, whereas the (100)- and (111)-oriented wires are characterized by an indirect band gap. For the same wire-effective size, an anisotropy in the fundamental band gap E-g with respect to the wire orientation is observed. For (110)-oriented wires, the imaginary part of the dielectric function shows a pronounced peak in the visible energy range with strong dimensionality and polarization dependence.