Stability of optically active charged excitons in quasi-two-dimensional systems

A negatively charged quasi-two-dimensional exciton (${\mathrm{X}}^{\mathrm{-}}$) is studied numerically in the presence of a uniform perpendicular B field. Various quasi-two-dimensional geometries are studied. The charge distribution of the ${\mathrm{X}}^{\mathrm{-}}$ parallel to the B field is found to be crucial in determining the stability of the optically active ${\mathrm{X}}^{\mathrm{-}}$ and hence its photoluminescence signature. The theory provides a quantitative explanation of recent experimental results obtained for a GaAs quantum well. Effects are found that cannot be described within a lowest-Landau-level approximation.