Metastable excitons in ${\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}/\mathrm{Z}\mathrm{n}}_{1-x}{\mathrm{Fe}}_x\mathrm{Se}$ quantum wells

We present an optical (reflectance and photoluminescence) study of metastable excitons in ${\mathrm{Z}\mathrm{n}\mathrm{S}\mathrm{e}/\mathrm{Z}\mathrm{n}}_{1-x}{\mathrm{Fe}}_x\mathrm{Se}$ quantum-well structures. These states are associated with the type-II $(-\frac{1}{2},-\frac{3}{2})$ ground-state exciton of the system. The metastable excitons are formed because the Coulomb attraction of the $m_j=-$ $\frac{1}{2}$ electron tends to localize the $m_j=-$ $\frac{3}{2}$ hole in the vicinity of the electron. This complex breaks apart as the temperature increases, and the system returns to its ground state in which the $m_j=-$ $\frac{1}{2}$ electron and the $m_j=-$ $\frac{3}{2}$ hole are segregated.