Strain effects on optical properties of tetrapod-shaped CdTe/CdS core-shell nanocrystals

TL;DR

This study theoretically investigates how strain affects the optical properties of tetrapod-shaped CdTe/CdS core-shell nanocrystals, revealing enhanced carrier separation and energy shifts relevant for optoelectronic applications.

Contribution

It provides a detailed theoretical analysis of strain effects on exciton states in tetrapod-shaped nanocrystals, highlighting differences from spherical structures and aligning with experimental data.

Findings

Strain promotes type-II carrier confinement in nanocrystals.

Strain causes a small blue shift in exciton energy.

Arm diameter influences strain and shell thickness effects.

Abstract

The exciton states of strained CdTe/CdS core-shell tetrapod-shaped nanocrystals were theoretically investigated by the numerical diagonalization of a configuration interaction Hamiltonian based on the single-band effective mass approximation. We found that the inclusion of strain promotes the type-II nature by confining the electrons and holes in nonadjacent regions. This carrier separation is more efficient than that with type-II spherical nanocrystals. The strain leads to a small blue shift of the lowest exciton energy. Its magnitude is smaller than the red shift induced by increasing the shell thickness. Moreover, the larger arm diameter reduces the influence of both shell thickness and strain on the exciton energy. Considering the broken symmetry, a randomness induced carrier separation was revealed which is unique to a branched core-shell structure. The calculated shell thickness dependence of the emission energy agrees well with available experimental data.