Doping-Induced Oxygen-Vacancy-Related Defects Drive Ultrafast Hole Trapping in Plasmonic Indium-Doped ZnO Nanocrystals

Aliovalent doping converts colloidal ZnO nanocrystals (NCs) into plasmonic n-type degenerate semiconductors, but its influence on nonequilibrium carrier relaxation remains insufficiently understood. Here, we show that oxygen-vacancy-related defects introduced by doping promote ultrafast hole trapping in indium-doped ZnO NCs. Raman spectra reveal a monotonic increase in vacancy-related phonon signatures with increasing In/Zn ratio, while broadband femtosecond transient absorption spectroscopy resolves a concomitant increase in the contribution of a sub-100 ps trap-associated component. The fast decay component is assigned to defect-mediated hole trapping, as trion Auger recombination can be ruled out based on the fluence-independent kinetics and size-based estimates. Rapid hole removal suppresses prompt electron-hole recombination, thereby preserving photogenerated electrons that modulate the localized surface plasmon resonance for more than 100 μs. These results establish a correlation among aliovalent doping, Raman-active vacancy modes, and defect-mediated hole trapping in plasmonic NCs.