IS THE EXCITON RYDBERG HUGE IN T-SHAPED QUANTUM WIRES

We have calculated the exciton binding energy R-X(th) and the exciton transition energy E-X(th) of T-shaped wires made of GaAs-Ga0.7Al0.3As (S1 series) and GaAs-AlAs (S2 series) without adjustable parameters. T he finite depth of the wells and the Gamma(8) cubic symmetry of the va lence band are explicitly taken into account. The theoretical results are compared with the experimental values E-X(exp) and the estimated v alues R-X(est) obtained for both S1 series and S2 series by Someya et al. We get a perfect agreement between E-X(exp) (1591 meV) and E-X(th) (1590 meV) in S1 series where R-X(est) = 17 +/- 3 meV and R-X(th) = 1 5 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 photolum inescence line, twice larger in S2 series than in S1 series, and the d iscrepancy between the experimental and theoretical values suggest tha t the luminescence is due to excitons bound to interfaces. We conclude that the values of the exciton binding energy is overestimated by abo ut 50%.