Electronic structure of InP/ZnSe quantum dots: effect of tetrahedral shape, valence band coupling and excitonic interactions

TL;DR

This study uses multi-band k·p theory to analyze the electronic and optical properties of tetrahedral InP/ZnSe quantum dots, revealing effects of shape, valence band coupling, and excitonic interactions on their spectra.

Contribution

It provides a detailed theoretical analysis of how tetrahedral shape and valence band coupling influence the electronic structure and excitonic interactions in InP/ZnSe quantum dots.

Findings

Near-band-edge excitonic spectrum resembles spherical nanocrystals.

Large QDs show transitions violating angular momentum selection rules.

Valence band coupling significantly affects hole state properties.

Abstract

The energy levels and optical transitions of tetrahedral core/shell InP/ZnSe quantum dots (QDs) are investigated by means of multi-band k$\cdot$p theory. Despite the $\overline{T}_d$ symmetry relaxing spherical selection rules, the near-band-edge excitonic spectrum is reminiscent of that obtained for spherical nanocrystals. Exceptions appear in large (red-emitting) QDs, where transitions violating the (quasi-)angular momentum selection rule ($\Delta L=0,\pm 2$) are observed, and the ground state does not become dark ($P_{3/2}$-like). Valence band coupling is important in determining the symmetry, degeneracy and energy of hole states, with split-off holes playing a greater role than in CdSe QDs. The ($1S_e$-like) electron ground state exhibits moderate delocalization into the ZnSe shell. The confinement regime is then strong even for thick shells, which results in Coulomb interactions being mostly perturbative. Electrons remain largely localized in the InP core even in negative trions, despite electron-electron repulsions. At the same time, the asymmetry between Coulomb attractions and repulsions leads to negative (positive) trions being bound (antibound) by tens of meV. The biexciton binding energy switches from positive to negative, depending on the QD size.