Anisotropic optical matrix elements in [hhk]-oriented quantum wires

Optical polarization properties in quantum wires (QWIs) are theoretically investigated as functions of wire crystallographic directions taking the valence band anisotropy into account. Optical matrix elements and gain spectra are calculated for GaAs cylindrical QWIs with infinite barriers. It is shown that the optical matrix element for light polarized to the wire direction shows weak dependence on the wire crystallographic direction. In contrast, the valence band anisotropy causes strong dependence on the wire direction for light polarized to the perpendicular directions, and large in-plane optical anisotropy appears for [110]- and [112]-oriented QWIs. It is considered, from the calculated results of the gain spectra, that a [111]-QWI laser shows the lowest threshold current and that the [1,−1,0]-QWIs on a (110) substrate are the most suitable for polarization controlled vertical cavity surface emitting lasers. These results indicate that the structural optimization from the viewpoint of the crystallographic direction is important for optical devices using QWIs.