Diffusion-Limited Kinetics of Isovalent Cation Exchange in III-V Nanocrystals Dispersed in Molten Salt Reaction Media.

The goal of this work is to determine the kinetic factors that govern isovalent cation exchange in III-V colloidal quantum dots using molten salts as the solvent and cation source. We focus on the reactions of InP + GaI3→ In1-xGaxP and InAs + GaI3→ In1-xGaxAs to create technologically important ternary III-V phases. We find that the molten salt reaction medium causes the transformation of nearly spherical InP nanocrystals to tetrahedron-shaped In1-xGaxP nanocrystals. Furthermore, we determine that the activation energy for the cation exchange reaction is 0.9 eV for incorporation of Ga into InP and 1.2 eV for incorporation of Ga into InAs, both much lower than the measured values in bulk semiconductors. Next, we use powder XRD simulations to constrain our understanding of the structure of the In1-xGaxP nanocrystals. Together our results reveal several important features of molten salt-mediated cation exchange and provide guidance for future development of these materials.