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Carrier Dynamics and Interactions for Bulklike Photoexcitation of Colloidal Indium Arsenide Quantum Dots
journal contribution
posted on 2018-12-10, 00:00 authored by Austin
P. Spencer, William K. Peters, Nathan R. Neale, David M. JonasThe
remarkable photonic and photochemical properties of colloidal
quantum dots (QD) depend critically on the dynamics of carrier interactions
and relaxation. Despite their importance, a quantitative experimental
evaluation of these processes has proven elusive due to the inherent
challenge of exactly separating single-exciton and multiexciton dynamics,
whose spectroscopic signatures overlap in time, spectrum, and excitation
fluence. Here, we measure pump-fluence-dependent absolute pump–probe
transients of indium arsenide QDs, refreshing the sample using beam
scanning to limit repetitive excitation. Focusing on the low fluence
limit near the onset of biexciton formation, excitation conditions
were precisely controlled and characterized by averaging Poisson-distributed
excitation statistics over all three spatial dimensions of the pump
and probe beam spatial profiles to determine the average excitation
probability. A saturation model is developed to uniquely decompose
the pump–probe signal into single-exciton and biexciton signals.
This method harnesses the distinct pump-fluence scaling of absolute
pump–probe signals from singly and doubly excited QDs without
any assumptions regarding the relative time scales or amplitudes of
single-exciton and biexciton signals. Probing in the bulklike region
of the QD absorption spectrum, the signal from biexcitons is found
to be 1.8 times the signal from single excitons at T = 0, consistent with the conventionally assumed factor of 2 within
the 95% confidence intervals. The biexciton signal contains the same
hot-carrier relaxation dynamics as that from single excitons, but
signal from a second exciton additionally exhibits a 26 ps exponential
decay attributed to Auger recombination.