Strain in Lattice-Mismatched CdSe-Based Core/Shell Nanoplatelets

Abstract

We investigate the role of stress arising between core and shell materials in colloidal CdSe/X hetero-nanoplatelets (X = ZnS, CdS, CdTe). The resulting strain distribution is calculated within the linear elastic regime and also its influence on the electronic structure with k·p theory. We show that strain shifts the energy of electrons and that of holes by several tens of megaelectronvolts (meV). In structures with type I band alignment, the two shifts have opposite signs and the net effect on the exciton emission energy is small, but both these add up in type II systems. The strain response in colloidal nanoplatelets (NPLs) is found to exhibit some differences as compared to that of epitaxial quantum wells, including a sizable influence of lateral dimensions below 10 nm and a potentially relevant effect of coupled strain–momentum terms of the Hamiltonian. We further show that an asymmetric shell covering leads to bending of the nanoplatelet and tilted potential profiles along the strong confinement direction, analogous to a built-in electric field. We propose overcoating CdSe/CdS NPLs with an outer ZnS shell as a method to mitigate the tunneling-induced red shift of emission via strain engineering.