Quasibound states in type-II ZnTe/CdSe superlattices studied by modulation spectroscopies and photoconductivity at room temperature

We report that the quasibound states at the above-barrier region in type-II ZnTe/CdSe superlattices can be clearly observed at room temperature by photoreflectance, contactless electroreflectance, as well as photoconductivity measurements. We provide concrete evidence to confirm that free-carrier confinement at barrier layer (either in the valence-band CdSe layer or in the conduction-band ZnTe layer) does exist. It is found that the barrier-width dependence of the above-barrier ground-state transition energies can be described well by the constructive interference condition. We also observe the absorptive spatially indirect transition between electrons confined in the CdSe and holes confined in the ZnTe layers.