Anisotropy of interband transitions in InAs quantum wires: an atomistic theory

The electronic and optical properties of [001]-oriented free-standing InAs cylindrical quantum wires (QWRs) with diameters 10-100 Å are calculated using an atomistic, empirical pseudopotential plane-wave method. We analyze the effect of different degrees of mixing between valence bands on the optical properties of these nanostructures, by switching on and off the spin-orbit interaction. The fundamental transition in these QWRs exhibit a large anisotropy, with emission polarized prevalently along the wire axis z. The magnitude of such an anisotropy is found to depend on both degree of valence band mixing and wire size. In higher energy interband transitions, we find anisotropies close to 100% with emission polarized perpendicular to the wire axis. Furthermore, in large wires, transitions involving highly excited valence states show in-plane polarization anisotropies between the [110] and [110] directions. InAs wires can therefore switch between z-polarized to xy-polarized emission/absorption for different excitation energies. This makes them ideally suited for application in orientation-sensitive devices.