Confining type-II spherical core-shell quantum dot heterostructures with narrow and wide band gaps

Using a single-band model, the lowest transition energy was analysed between the lowest unoccupied molecular orbital (LUMO) of the conduction band and the highest occupied molecular orbital (HOMO) of the valence band. We focus on categorising the confinement strength in type-II core-shell quantum dots (CSQDs) based on the step-potential and show how it will affect their transition energy. Our model is applied to CSQDs of the heterostructures PbS/CdS and ZnTe/ZnSe through narrow and wide band gaps, respectively. It found that PbS/CdS CSQDs demonstrates a strong confinement in which their transition energy would increase more compared to its weak confinement case in ZnTe/ZnSe CSQDs. The weak confinement case also demonstrated both blue-shift and red-shift of photoluminescence emission compared to the bulk ZnTe and ZnSe for which it can be inferred as pseudo type-II CSQDs. This would help experimentalists to tune the transition energy of type-II model in order to fabricate photons with longer carrier lifetime compared to the type-I model.