Optical absorption of wide quantum wires

We have calculated absorption spectra of quantum wires with rectangular cross-section and finite barrier height, accounting for the Coulombic mixing between subbands. Our method gives high-resolution spectra for both the bound and continuum states. We use these spectra to investigate the exciton binding energy and oscillator strength as a function of confinement, particularly discussing the quasi-one-dimensional (1D) to quasi-2D transition which occurs when one of the wire dimensions is increased. The spectra show Fano resonances in the continuum region, caused by the resonant coupling between discrete and energetically degenerate continuum states. The Fano resonance is characterized by an asymmetrically broadened peak and a dip below the level of the surrounding continuum. The broadening of these peaks is typically in the. region of 1 meV.