Excitons, Biexcitons and Dephasing in GaAs T-shaped quantum wires

The binding energy of excitons and biexcitons and the exciton dephasing in T-shaped GaAs quantum wires is investigated by transient four-wave mixing. The T-shaped structure is fabricated by cleaved-edge overgrowth and its geometry is engineered to optimize the one-dimensional confinement. In this wire of 6.6x24 nm2 size we find a one-dimensional confinement of more than 20meV, an inhomogeneous broadening of only 3.4 meV. The measured exciton binding energy of 12 meV is in good agreement with numerical calculations. The biexciton binding energy of 2.0 meV is less than in comparable quantum well structures due to the different confinement of electron and hole in the T-shaped wire. A dispersion of the homogeneous linewidth within the inhomogeneous broadening due to phonon-assisted relaxation is observed. An exciton acoustic-phonon scattering coefficient of 6.1 +-0.5 ìeV/K is found, which is larger than in comparable quantum-well structures.