Quantum confinement of excitons in the spin-orbit-split-off band in ZnSe/ZnS strained-layer superlattices

We report the observation of two-dimensional (2D) electronic states confined in the spin-orbit-split-off band in ZnSe/ZnS strained-layer superlattices. The steplike absorption edge at the ${\mathit{E}}_0$+${\mathrm{\Delta }}_0$ gap and the corresponding 2D exciton peak have been clearly identified in spectroscopic-ellipsometry spectra. The 2D-exciton Rydberg energy obtained is about 160 meV, which is considerably larger than that at the ${\mathit{E}}_0$+${\mathrm{\Delta }}_0$ gap of bulk ZnSe (∼40 meV). Calculated steplike-edge energies using the model-solid approach and the Kronig-Penney model agree well with the experimental observations.