Is the Exciton Rydberg Huge in T-Shaped Quantum Wires?

We have calculated the exciton binding energy R^th_X and the exciton transition energy E^th_X of T-shaped wires made of GaAs–Ga_0.7Al_0.3As (S1 series) and GaAs–AlAs (S2 series) without adjustable parameters. The finite depth of the wells and the Γ₈ cubic symmetry of the valence band are explicitly taken into account. The theoretical results are compared with the experimental values E^exp_X and the estimated values R^est_X obtained for both S1 series and S2 series by Someya et al. We get a perfect agreement between E^exp_X (1591 meV) and E^th_X (1590 meV) in S1 series where R^est_X = 17 ± 3 meV and R^th_X = 15 meV. On the contrary we do not get the same agreement in S2 series (1626, 1621, 27 ± 3, 18 meV, respectively). The width of the photoluminescence line, twice larger in S2 series than in S1 series, and the discrepancy between the experimental and theoretical values suggest that the luminescence is due to excitons bound to interfaces. We conclude that the values of the exciton binding energy is overestimated by about 50%.