Structural Hole Traps in III-V Quantum Dots

TL;DR

This paper investigates the origin of trap states in non-toxic III-V quantum dots, revealing that fully-coordinated atoms with distorted geometries create structural traps that impact their performance and are insensitive to surface ligands.

Contribution

It provides computational evidence and a molecular orbital explanation for structural trap states caused by geometric distortions in InP and GaP QDs, expanding understanding beyond under-coordinated surface defects.

Findings

Structural traps arise from bond stretches and angular distortions.

These traps are insensitive to ligand choice.

Core-shell passivation may not eliminate these defects.

Abstract

Non-toxic III-V quantum dots (QDs) are plagued with a higher density of performance-limiting trap states than II-VI and IV-VI QDs. Such trap states are generally understood to arise from under-coordinated atoms on the QD surface. Here, we present computational evidence for, and an exploration of, trap states in InP and GaP QDs that arise from fully-coordinated atoms with distorted geometries, denoted here as structural traps. In particular, we focus on the properties of anion-centered hole traps, which we show to be relatively insensitive to the choice of the (typically cation-coordinating) ligand. Through interpolation of trap center cutouts, we arrive at a simple molecular orbital (MO) argument for the existence of structural traps, finding two main modalities: bond stretches and angular distortion to a see-saw-like geometry. These structural trap states will be important for understanding the low performance of III-V QDs, as even core-shell passivation may not remove these defects unless they can rigidify the structure. Moreover, they may lead to interesting dynamical properties as distorted structures could form transiently.