Understanding Trap States in InP and GaP Quantum Dots through Density Functional Theory

The widespread application of III–V
colloidal
quantum dots
(QDs) as nontoxic, highly tunable emitters is stymied by their high
density of trap states. Here, we utilize density functional theory
(DFT) to investigate trap state formation in a diverse set of realistically
passivated core-only InP and GaP QDs. Through orbital localization
techniques, we deconvolute the dense manifold of trap states to allow
for detailed assignment of surface defects. We find that the three-coordinate
species dominate trapping in III–V QDs and identify features
in the geometry and charge environment of trap centers capable of
deepening, or sometimes passivating, traps. Furthermore, we observe
stark differences in surface reconstruction between InP and GaP, where
the more labile InP reconstructs to passivate three-coordinate indium
at the cost of distortion elsewhere. These results offer explanations
for experimentally observed trapping behavior and suggest new avenues
for controlling trap states in III–V QDs.