Importance of core and shell sizes in the localization of the electron and hole in the formation of type I or type II excitons in spherical CdSe/ZnTe and CdSe/CdTe quantum dots.

Semiconductor core/shell quantum dots represent a promising class of nanostructure that can provide new techniques of control for performing the electronic and optical properties. Through each combination formed by the core and the shell radii and the confinement effect, the trapped charge carries behave differently, which obviously has a direct effect on the semiconductor properties. Studying the behavior of charge carriers is one of the most important steps in understanding the semiconductor performance when it undergoes certain conditions, which inevitably can offer other benefits for various applications. The electron and hole localizations strongly depend on core and shell sizes, but determining these limit sizes has not been sufficiently discussed in the literature. This paper gives a detailed theoretical study describing the three cases of electron and hole positions in two different type II core/shell quantum dots, CdSe/ZnTe and CdSe/CdTe considering the core and shell sizes. Our numerical calculations show that two significant critical radii of the core allow to switch between the exciton type I and type II quasi-particle. As a function of the shell thickness, the ground state energy of the electron is found to be higher when the core radius is small; contrariwise, the hole ground state energy remains smaller. Afterward, these specific variations influence the ground state binding energy of the correlated electron–hole quasi-particle (exciton), leading to a particular behavior of this energy as a function of the core and shell sizes.