Magneto-optical studies of the type-I/type-II crossover and band offset in ZnTe/${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Mn}}_{\mathit{x}}$Te superlattices in magnetic fields up to 45 T

We report measurements of magnetoreflectivity in ZnTe/${\mathrm{Zn}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Mn}}_{\mathit{x}}$Te superlattices with varying well width in magnetic fields up to 45 T. From an analysis of the Zeeman splitting, we investigate the change of band alignment with field and the band offset ratio. A crossing of the 1s exciton transitions from the ZnTe buffer layer and the 1s heavy hole ${\mathrm{\sigma }}_{+}$ exciton of the superlattice is observed, providing unambiguous evidence of a band alignment change from type I to type II. The excitonic energy levels for both type-I and type-II band structure are calculated using a variational method. This model fits the experimental data very well at high fields for both ${\mathrm{\sigma }}_{+}$ and ${\mathrm{\sigma }}_{\mathrm{-}}$ transitions and predicts that the type-I/type-II crossover occurs at 2–3 T. Also by fitting the ${\mathrm{\sigma }}_{+}$ transition energy as a function of field a conduction band offset ratio of Δ${\mathit{E}}_{\mathit{c}}$/Δ${\mathit{E}}_{\mathit{g}}$=0.72±0.04 is deduced.