Understanding electric field control of electronic and optical properties of strongly-coupled multi-layer quantum dot molecules

TL;DR

This study uses atomistic calculations to explore how electric fields influence the electronic and optical properties of strongly-coupled quantum dot molecules, providing insights for device engineering in optoelectronics and solar cells.

Contribution

It offers a comprehensive analysis of electric field effects on QDMs, including wave function symmetry, transition energies, and band structure transformations, advancing understanding for device optimization.

Findings

Electric fields can balance strain-induced asymmetry in electron states.

Large electric fields break interdot coupling, inducing a transition to type-II band structure.

QDMs can be tuned for high dipole moments or polarizability depending on electric field strength.

Abstract

Strongly-coupled quantum dot molecules (QDMs) are widely deployed in the design of a variety of optoelectronic, photovoltaic, and quantum information devices. An efficient and optimized performance of these devices demands engineering of the electronic and optical properties of the underlying QDMs. The application of electric fields offers a knob to realise such control over the QDM characteristics for a desired device operation. We perform multi-million-atom atomistic tight-binding calculations to study the influence of electric fields on the electron and hole wave function confinements and symmetries, the ground-state transition energies, the band-gap wavelengths, and the optical transition modes. The electrical fields both parallel ($\vec{E_p}$) and anti-parallel ($\vec{E_a}$) to the growth direction are investigated to provide a comprehensive guide on the understanding of the electric field effects. The strain-induced asymmetry of the hybridized electron states is found to be weak and can be balanced by applying a small $\vec{E_a}$ electric field, of the order of 1 KV/cm. The strong interdot couplings completely break down at large electric fields, leading to single QD states confined at the opposite edges of the QDM. This mimics a transformation from a type-I band structure to a type-II band structure for the QDMs, which is a critical requirement for the design of intermediate-band solar cells (IBSC). The analysis of the field-dependent ground-state transition energies reveal that the QDM can be operated both as a high dipole moment device by applying large electric fields and as a high polarizibility device under the application of small electric field magnitudes. [abstract is truncated to fit the character count of arXiv]