Electric field orientation and dielectric confinement control of the impurity photoionization in CdSe nanoplatelets

In this study, the influence of the in-plane electric field and dielectric confinement on impurity states in CdSe nanoplatelets was investigated theoretically and numerically using the Finite Element Method. The photoionization of a hydrogen-like donor impurity was studied for various orientations of the electric field in the plane of the nanoplatelet, accounting for polarization along the axial direction within the Takagahara model. We demonstrate that an increase in NPL thickness enhances the spatial overlap between bound and excited states through axial delocalization, while the dielectric constant of the surrounding medium primarily modulates transition energies. Analysis of electric-field dynamics reveals that in-plane fields induce significant spectral shifts and peak damping. Furthermore, we establish the profound role of spatial anisotropy, observing a strong dependence of the binding energy and oscillator strength on the field angle. This behavior is shown to be highly sensitive to different impurity positions within the nanoplatelet. Notably, positioning the impurity at the NPL corner breaks spatial inversion symmetry, resulting in increased photoionization intensity and the emergence of a second transition peak. These findings demonstrate that CdSe NPLs are promising candidates for tunable optoelectronic devices and field-sensitive nanosensors through the precise modification of field magnitude, direction, and dielectric mismatch.