Formation of type-II excitons in CdTe/Cd1-xMnxTe superlattices at high magnetic fields

We report measurements of magnetoreflectivity in CdTe/Cd1-xMnxTe superlattices with varying manganese concentration in magnetic fields up to 45 T. from an analysis of the 1s heavy-hole sigma(+) transition, we observe that the energy shift is directly equal to the shift in the valence-band edge of the barrier layer. This provides a clear proof of type-I-type-II crossover in this system. The critical magnetic field that leads to the formation of a type-II exciton is also estimated. We point out that the criterion for the observation of a type-II exciton is that the type-II valence-band offset has to be larger than the binding energy of an exciton.