Theoretical and experimental investigation of electronic structure and relaxation of colloidal nanocrystalline indium phosphide quantum dots

We present results of theoretical studies of the electronic structure, and experimental studies of electronic relaxation dynamics, for colloidally synthesized InP quantum dots (QD’s). Detailed theoretical calculations of the electronic structure of a 41.8 Å diameter InP QD, based on an atomistic pseudopotiential approach, are presented and discussed in the context of experimental measurements. Using femtosecond transient absorption (TA) spectroscopy, we find that the rate of relaxation of photogenerated excitons to the lowest-energy exciton level varies depending upon excitation energy and surface chemistry. Etching the QD’s passivates surface electron traps and yields enhanced carrier cooling, which we ascribe to improved confinement of charge carriers to the QD core. When exciting near or slightly above the first exciton state, we observe a sub-picosecond decay of the band edge TA bleach signal which we attribute to a thermalization process. We also present size-selective transient absorption measurements providing experimental evidence which confirms the existence of two s-like exciton states spaced by ∼100 meV.