Band alignment in ZnSe/${\mathrm{Zn}}_{1\mathrm{-}\mathrm{x}\mathrm{-}\mathrm{y}}$ ${\mathrm{Cd}}_{\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{y}}$ Se quantum-well structures

We present a magneto-optical study of ZnSe/${\mathrm{Zn}}_{1\mathrm{-}\mathrm{x}\mathrm{-}\mathrm{y}}$ ${\mathrm{Cd}}_{\mathrm{x}}$ ${\mathrm{Mn}}_{\mathrm{y}}$ Se quantum-well structures in which a suitable choice of the Cd composition leads to a system that is type I at zero magnetic field. When a magnetic field is applied perpendicular to the layers of the structure, the band edges split in such a way as to make the upper ${\mathbf{\sigma }}_{\mathrm{-}}$ (+, +) exciton transition type II, while the ground state ${\mathbf{\sigma }}_{+}$ (-, -) exciton component remains type I at all field values. This alignment reduces the probability for carrier relaxation from the higher-energy exciton component and opens the possibility of hole-spin population inversion via optical pumping.