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

The implementation of non-toxic, highly tunable III-V quantum dots (QDs) for emission is held back by low PLQY arising from trap states. Here, we apply density functional theory (DFT) to study trap states in a diverse set of realistic core-only InP and GaP QDs. Orbital localization allows us to deconvolute dense manifolds of trap states at the band edges to facilitate detailed study of surface defects. We show that three-coordinate species are the primary origin of trap states in III-V QDs and identify geometric and charge features which modulate and suppress the depth of traps. We observe different surface reconstruction in InP and GaP, where the more labile InP reconstructs to passivate three-coordinate indium at the cost of distortion elsewhere. This distortion gives rise in turn to trap states arising from four-coordinate cations and anions, denoted here as structural trap states. We delve deeper into the nature of these structural trap states here, investigating the prevalence of different types and providing intuitive arguments for their origin.