Seminarium Fizyki Politechniki Wrocławskiej
PWr, bud. A1, sala 322
Atomistic approach for modeling the spectral and spin properties of III–V and Group IV quantum dot systems
dr hab. inż. Krzysztof Gawarecki
Instytut Fizyki Teoretycznej, Politechnika Wrocławska
The optical spectra of semiconductor quantum dots are typically dominated by the emission lines corresponding to direct excitonic recombination. However, the interplay of Coulomb interaction and symmetry breaking leads to additional spectral features such as radiative Auger transitions. This process introduces red-shifted emission lines, offering a unique opportunity to probe single-particle excitation energies in the quantum dot spectrum that would otherwise remain inaccessible [1].
In our joint theoretical-experimental work [2], we present measurements of such radiative Auger lines for a range of InGaAs/GaAs self-assembled quantum dots. Within a realistic sp3d5s∗ tight-binding model combined with configuration-interaction approach, we calculate the emission from a negative trion. We get a very good agreement between the theory and the experimental data. We investigate the role of symmetry and show that correct ordering of the emission lines can be obtained assuming symmetry breaking by alloy disorder. We also provide in-depth analysis based on the group theory. The presented theoretical model and results give insight into the interplay between the symmetry breaking and the position and strength of the radiative Auger lines.
The second part of the talk will be devoted to GeSn and Ge QD systems. The GeSn alloy attracts much attention due to its band gap dependence on the composition: at some critical Sn content (of a few percent), the bulk changes its character from the indirect- to the direct band gap [3]. The other properties of GeSn, like high carrier mobility, makes this material interesting from the point of view of applications for optoelectronic devices. We calculate the electron and hole states of GeSn colloidal quantum dots and investigate the interplay of confinement effect and composition-induced indirect-direct band gap transition [4]. Finally, we study the hyperfine interaction for the ground light-hole states in an electrically-defined QDs (in GeSn/Ge/GeSn QW) [5]. We show that the conduction-valence band mixing, leads to considerable s-type admixtures to the hole states, providing the dominant channel of hyperfine coupling due to the Fermi contact interaction.
[1] M. C. Löbl, C. Spinnler, A. Javadi, L. Zhai, G. N. Nguyen, J. Ritzmann, L. Midolo, P. Lodahl, A. D. Wieck, A. Ludwig, and R. J. Warburton, Nat. Nanotechnol. 15, 558 (2020).
[2] K. Gawarecki, C. Spinnler, L. Zhai, G. N. Nguyen, A. Ludwig, R. J. Warburton, M. C. Löbl, D. E. Reiter, P. Machnikowski, Phys. Rev. B 108 235410 (2023).
[3] W. Wegscheider, K. Eberl, U. Menczigar, G. Abstreiter, Appl. Phys. Lett. 57 (9) (1990) 875877.
[4] K. Gawarecki, J. Ziembicki, P. Scharoch, R. Kudrawiec, J. Appl. Phys. 135, 214303 (2024)
[5] A. Miętkiewicz, J. Ziembicki, K. Gawarecki, arXiv:2507.12249 (2025)
