Effect of the Interfacial Potential on Elementary Exciton Processes in InP-Based Core/Shell Quantum Dots
Kazuki Inada, Daichi Eguchi, Naoto Tamai
Abstract
In core/shell quantum dots (c/s QDs), the interfacial potential between the core and shell affects elementary exciton processes, such as radiative and nonradiative processes, including Auger recombination. Therefore, a comprehensive understanding of the impact of the interfacial potential in c/s QDs is imperative for diverse applications, ranging from light-emitting diodes (LEDs) to lasers. We investigated the effect of the interfacial potential on elementary exciton processes in InP-based c/s QDs by using femtosecond transient absorption spectroscopy (fs-TAS). We synthesized c/s QDs with diverse interfacial potentials: steep ones (InP/ZnS and InP/ZnSe QDs) and a smooth counterpart (InP/ZnSe x S 1– x /ZnS QDs). The steady-state absorption and luminescence spectra obtained from aliquots extracted during the synthesis of InP/ZnSe x S 1– x /ZnS QDs and the EDS line profile revealed the formation of a compositional gradient shell (smoothed interfacial potential). In the single-exciton regime, elementary exciton processes were examined by global-target analysis, and electron transfer from the ZnSe shell to the InP core in c/s QDs was observed within the subpicosecond scale. The rate of Auger recombination in InP/ZnSe x S 1– x /ZnS QDs QDs was ∼8 times slower than that in InP/ZnS QDs of the same volume. This suppression can be explained by the effective electron wave function penetration from the core into the shell and the reduced carrier momentum in the final state resulting from the smoothed interfacial potential. These findings provide important guidelines for the rational design of interfacial potentials in InP-based c/s QDs for various applications such as in LEDs and laser devices.