Screening effects on the optical properties of II-VI wurtzite ZnO/MgO quantum dots

The screening effects on the light emission characteristics of wurtzite (WZ) ZnO/MgZnO quantum dots (QDs) were investigated as a function of carrier density. These results were compared with those without the screening effect. The light emission intensity is shown to be significantly affected by the screening effect. The difference of the light intensity between cases with and without screening effect gradually increases with increasing carrier density. This can be explained by the fact that the overlap between the electron and hole wave functions, and therefore the optical matrix element, is enhanced due to the increase in the screening effect with increasing carrier density. Also, the peak wavelength for the self-consistent solution is observed to be blueshifted with increasing carrier density because the optical matrix elements corresponding to transitions from the conduction subband to higher valence subbands become dominant at a higher carrier density. We observe that the screening effect is enhanced rapidly with increasing dot size. In the case of the ZnO/MgO QD grown on MgO substrate, there exist a large potential due to the strain-induced piezoelectric polarization, in addition to the spontaneous polarization. As a result, its light emission intensity is shown to be much smaller than that of ZnO/MgO QD grown on ZnO substrate.