Excitons in T-shaped quantum wires - art. no. 205317

We calculate energies, oscillator strengths for radiative recombination, an d two-particle wave functions for the ground-state exciton and around 100 e xcited states in a T-shaped quantum wire. We include the single-particle po tential and the Coulomb interaction between the electron and hole on an equ al footing, and perform exact diagonalization of the two-particle problem w ithin a finite-basis set. We calculate spectra for all of the experimentall y studied cases of T-shaped wires including symmetric and asymmetric GaAs/A lxGa1-xAs and InyGa1-yAs/AlxGa1-xAs structures. We study in detail the shap e of the wave functions to gain insight into the nature of the various stat es for selected symmetric and asymmetric wires in which laser emission has been experimentally observed. We also calculate the binding energy of the g round-state exciton and the confinement energy of the one-dimensional (1D) quantum-wire-exciton state with respect to the 2D quantum-well exciton for a wide range of structures, varying the well width and the Al molar fractio n x. We find that the largest binding energy of any wire constructed to dat e is 16.5 meV. We also notice that in asymmetric structures, the confinemen t energy is enhanced with respect to the symmetric forms with comparable pa rameters but the binding energy of the exciton is then lower than in the sy mmetric structures. For GaAs/AlxGa1-xAs wires we obtain an upper limit for the binding energy of around 25 meV in a 10-Angstrom -wide GaAs/AlAs struct ure that suggests that other materials must be explored in order to achieve room-temperature applications. There are some indications that InyGa1-yAs/ A(l)xGa(1-x)As might be a good candidate.