Atomistic Approach to Exciton-Phonon Couplings in Semiconductor Quantum Dots

TL;DR

This work delivers an atomistic, parameter-light pipeline to predict exciton–phonon coupling in semiconductor quantum dots by marrying ab initio–informed tight-binding with configuration-interaction in an open-quantum-system framework. It computes excitonic complexes (X, XX, X$^-$, X$^+$), their radiative lifetimes, and, crucially, the phonon spectral densities $J^{\lambda-\lambda'}(\omega)$ without relying on simplified confinement models. The results reveal that while low-frequency behavior agrees with analytical expectations, atomistic $J(\omega)$ exhibits a high-energy tail driven by realistic dot geometry and wave functions, with configuration mixing playing a minor role. These insights, demonstrated on InAsP/InP nanowire QDs, translate into substantially altered phonon-assisted brightness for off-resonant excitation, underscoring the importance of atomistic detail for design and control of QD photonic devices. The framework thus enables geometry-by-design optimization of QD phonon environments and is extendable to other low-dimensional platforms where non-Markovian dynamics govern device performance.

Abstract

We present a fully atomistic approach to exciton-phonon coupling in semiconductor quantum dots that bridges microscopic electronic-structure calculations with non-Markovian open-quantum-system dynamics. On the example of an InAsP quantum dot embedded in an InP matrix, we compute single-particle states using an ab initio-parametrized tight-binding model, then obtain correlated many-body wave functions of neutral excitons, biexcitons, and charged trions via the configuration-interaction method. Using these correlated states, we compute the exciton-phonon coupling matrix elements. The resulting phonon spectral densities for different excitonic complexes are compared with the widely used analytical super-Ohmic form and reveal deviations at higher energies originating from the realistic dot geometry and atomistic wave functions, whereas configuration mixing is found to play only a minor role. Furthermore, we extract radiative lifetimes comparable to values experimentally measured. As a direct application, we simulate the emission brightness of a pulsed-driven quantum dot and demonstrate that the atomistically derived spectral density substantially broadens the region of efficient off-resonant excitation compared to the analytical model. The presented framework provides a nearly parameter-free route to simulate the non-Markovian open quantum dynamics in semiconductor quantum dots.

Figures (5)

• Figure 1: Schematic workflow of the theoretical framework. Starting from the atomic structure, parametrized either by ab initio or empirical methods, strain relaxation is followed by atomistic tight-binding calculations and configuration interaction to obtain many-body wavefunctions and energies. These serve as input for the evaluation of light–matter coupling (dipole matrix elements, radiative lifetimes) and for modeling the quantum-dot–phonon interaction. The resulting information enters a non-Markovian open quantum systems simulation, which can provide the time-dependent density matrix, expectation values, emission spectra, and population dynamics.
• Figure 2: (a) Top of view of the InAsP/InP QD. The QD is formed in the center by replacement of Phosphorus (blue circles) by Arsenic (green circles) forming a cylindrical QD in the center. (b) Side view of the structure highlighting the spatial distribution of the active region. Panel (c) shows the single-particle TB spectrum with the corresponding charge densities for the top valence band state and lowest-energy conduction band state. (d) Low-energy exciton and multi-exciton spectral lines, showing the exciton neutral exciton ($X$), biexciton ($XX$), negative trion ($X^-$), and positive trion ($X^+$) transitions.
• Figure 3: (a) Comparison of the numerically obtained phonon spectral density for the neutral exciton, with the non-correlated electron-hole only contribution and the corresponding analytical expression defined in Eq. \ref{['eq: AnalyticalSpectralDensity']}. (b) Phonon spectral densities for the lowest-energy excitonic complexes, including the exciton ($X$), biexciton ($XX$), and trions ($X^-$, $X^+$), showing nearly identical behavior across all cases.
• Figure 4: Phonon spectral densities for different QD heights $h$. Solid lines show the numerically computed spectral densities, while dashed lines indicate the corresponding analytical results.
• Figure 5: Calculated brightness $\mathcal{B}$ of the InAsP/InP QD as a function of pulse area $A$ and detuning $\delta$. The left panel (a) shows results obtained using the analytical phonon spectral density, while the right panel (b) displays results based on the numerically computed spectral density. The comparison highlights the impact of atomistic corrections to the exciton–phonon coupling on an experimentally relevant observable.