Regensburg 2025 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 31: Focus Session: Young Semiconductor Forum Poster

HL 31.5: Poster

Wednesday, March 19, 2025, 12:15–13:00, H13

Effects of atomistic fluctuations on the excitonic fine-structure in alloyed colloidal quantum Dots — •Anne Nadine Tewonoue Djota, Surender Kumar, and Gabriel Bester — Institute of physical chemistry and physics, University of Hamburg

The electron-hole exchange interaction in the presence of spin-orbit coupling leads for an atomistic calculation to a small energy splitting of the excitonic state known in this context as the fine structure splitting (FSS). Although this splitting is typically small, it has large consequences for the optical properties. For instance, the photoluminescence originates from these few states and is governed by the splitting (giving rise to temperature dependence) and polarization of these low energy excitonic states. So far most of the theoretical modeling has assumed that high symmetry structures lead to a simple dark-bright splitting with a large degeneracy of the excitonic states. In this work, we show based on atomistic calculations, that even globally perfectly symmetric structures (i.e., as far as an atomistic construction permits a "spherical" quantum dot) show a qualitatively different FSS as soon as alloying is introduced. The alloying effect is significantly stronger than any global shape anisotropy where the symmetry is broken for instance by geometrical elongation of the quantum dot. On the other hand, alloying a quantum dot through processes such as cation exchange is inherently random. As a result, different random alloy configurations with the same size and composition can exhibit significantly different FSS.

Keywords: Fine Structure; Cation Exchange; Alloyed quantum dots