Two-dimensional Nature of Center-of-mass Excitons Confined in a Single CdMnTe/CdTe/CdMnTe Heterostructure

We have investigated the dimensional nature of center-of-mass exciton confinement states in a CdMnTe/CdTe/CdMnTe heterostructure, where the CdTe well is too wide (144 nm) to confine both electrons and holes but able to confine whole excitons in the center-of-mass coordinate. Fine multiple photoluminescence spectra with a few meV separation were observed at 6 K. From the thickness dependence of the transition rate, they were attributed to even numbered center-of-mass exciton confinement states (N=2, 4, 6, ..., 18). Dimensionality of the center-of-mass exciton confinement states was also investigated in terms of temperature dependence of radiative decay time. At low temperatures (less than or similar to 12 K), we found that the ground state excitons are likely localized possibly due to the barrier interface fluctuation, resulting in a constant decay time (similar to 350 ps). With increased temperature (greater than or similar to 12 K), localized excitons are thermally released, giving rise to a linear temperature dependence of radiative decay time as an evidence of two-dimensional nature.