Quantum-confined Stark effect on spatially indirect excitons in CdTe/${\mathrm{Cd}}_{\mathrm{x}}$ ${\mathrm{Zn}}_{1\mathrm{-}\mathrm{x}}$ Te quantum wells

The quantum-confined Stark effect is studied in the mixed type-I/type-II CdTe/${\mathrm{Cd}}_{\mathrm{x}}$ ${\mathrm{Zn}}_{1\mathrm{-}\mathrm{x}}$ Te strained heterostructures. The type-II nature of the light-hole excitons is unambiguously confirmed by the blueshift observed under increasing electric field, in good agreement with calculations. On the other hand, the heavy-hole excitons are redshifted as expected for type-I excitons. The peculiar valence-band alignment, resulting from the sign reversal of the strain between the wells and the barriers, is used to detect the electric-field induced mixing of ${\mathrm{LH}}_1$ and ${\mathrm{HH}}_2$ confined hole states. An accurate value for the long-disputed chemical valence-band offset of CdTe/ZnTe system is extracted as Δ${\mathrm{E}}_{\mathrm{V}}$=(11±3)% of the band-gap difference between unstrained CdTe and ZnTe materials.