Optical properties of an exciton in core/shell/shell spherical quantum dot under an electric field

Abstract

We investigate the excitonic properties of spherical ZnS/CdS/ZnS core/shell/shell quantum dots under the influence of an external electric field. The system is modelled by solving the Schrödinger equation within the effective mass approximation using the finite element method. Exciton binding energies are computed via first-order perturbation theory. Using experimentally informed material parameters, we examine how exciton energy levels, oscillator strength, and exciton radiative lifetimes of the first three excited states ($1S$, $2S$, and $3S$) vary with changes in the inner and intermediate shell radii and applied electric field strength. The results highlight distinct features of the quantum-confined Stark effect, including electric-field-induced redshifts, degeneracies in exciton energy levels, and modifications in optical transitions. Notably, the intermediate shell radius has a more pronounced impact on excitonic behaviour than the inner radius. Increasing shell radii reduce quantum confinement, enhancing the influence of the electric field. The oscillator strength generally decreases with field strength, except for the $3S$ state, which exhibits non-monotonic behaviour due to carrier instability. Exciton radiative lifetime is strongly affected by the spatial redistribution of carriers under the electric field, showing monotonic trends for the ground state and non-monotonic variations for excited states. These findings offer insights into tailoring excitonic responses in semiconductor quantum dots through geometric and external-field control, with potential applications in optoelectronic and quantum devices.