Fast Electron and Slow Hole Relaxation in InP-Based Colloidal Quantum Dots

Area of Science:

• Materials Science
• Optoelectronics
• Quantum Dot Technology

Background:

• Colloidal indium phosphide (InP)-based quantum dots are eco-friendly alternatives to cadmium-based quantum dots for light-emitting applications.
• Understanding charge carrier dynamics, specifically relaxation pathways after excitation, is crucial for optimizing optoelectronic device performance.

Purpose of the Study:

• To investigate the charge carrier relaxation dynamics in colloidal InP/ZnS and InP/ZnSe core/shell quantum dots.
• To determine how initial excess energy influences electron and hole relaxation processes.
• To elucidate the mechanisms governing relaxation and their impact on radiative efficiency.

Main Methods:

• Time-resolved differential transmission spectroscopy was employed.
• Optical excitation and probing of individual transitions allowed for distinguishing electron and hole relaxation.
• Analysis focused on the influence of excess energy on relaxation pathways.

Main Results:

• Contrary to expectations, electrons relaxed faster than holes.
• Fast electron relaxation was attributed to an efficient Auger-like electron-hole scattering mechanism.
• Hole relaxation was slowed by small core-shell wave function overlap and interface trapping, leading to detrapping or non-radiative recombination.

Conclusions:

• The study reveals that electron relaxation in InP quantum dots is dominated by Auger-like processes, while hole relaxation is hindered by interface effects.
• Maximizing radiative efficiency requires device designs that inject charge carriers with minimal excess energy, close to their emitting states.