Hydrogenic donor in a CdSe/CdS quantum dot: Effect of electric field strength, nanodot shape and dielectric environment on the energy spectrum

The impact of an external electric field on the binding energy of a single donor impurity was examined within the effective-mass approach by deploying a variational calculation. The discontinuity of the permittivity, ɛr, and of the particle effective mass, mi*r, at the nanosystem boundaries was considered. Using the image charge approach, the impact of the surrounding medium on the shallow donor energy spectrum was also taken into account. Our theoretical investigation shows that, for zero electric field and when the shell thickness is taken constant, the increase of the core material size leads to decrease the single donor correlation energy. Further, for a fixed core material size the energy decreases quickly when the shell thickness moves from 0 to 1 nm, while it decreases very slowly when the shell thickness is ranged between 1 nm and 4 nm. On the other hand, we have established that when we turn on an external electric field, the probability density of confined particles tends to move towards the nanodot border which naturally shifts the energy spectrum to lower energies (redshift). It was also obtained that the donor Stark shift depends not only on the nanodot size, but also on the surrounding medium.