Vanishing fine structure splitting in highly asymmetric InAs/InP quantum dots without wetting layer

Area of Science:

• Materials Science
• Condensed Matter Physics
• Quantum Mechanics

Background:

• Simplified theoretical models often predict a monotonic relationship between quantum dot (QD) shape and excitonic state splitting.
• Understanding the influence of shape anisotropy on excitonic properties is crucial for designing advanced optoelectronic devices.

Purpose of the Study:

• To investigate the impact of in-plane shape elongation on the splitting of the lowest optically active excitonic states in quantum dots.
• To explore the role of alloy randomness and wetting layers in modulating these shape-dependent effects.

Main Methods:

• Atomistic calculations were employed to simulate quantum dot structures.
• The study focused on shape-anisotropic nanostructures, considering realistic elongation ratios and the presence/absence of wetting layers.

Main Results:

• Sufficiently large in-plane shape elongation can decrease or even reverse the splitting of the two lowest optically active excitonic states.
• This effect is prominent in shape-anisotropic nanostructures without a wetting layer but is significantly diminished by alloy randomness due to InAs/InP intermixing.
• Dark-exciton spectra are largely unaffected by alloying and are primarily influenced by lateral elongation.

Conclusions:

• Quantum dot shape anisotropy plays a critical role in excitonic fine-structure splitting, challenging simplified theoretical predictions.
• Alloy randomness in quantum dot (QD) structures complicates the shape dependence of fine-structure splitting, justifying simpler models in some practical scenarios.
• Lateral elongation remains a dominant factor for dark-exciton spectra, irrespective of alloying effects.