Doctoral Examination: Auger-dominated carrier recombination and relaxation dynamics within cdse-based nanoplatelets

Yana Wang, supervised by Dr. Stephen K. O’Leary, will defend their dissertation titled “Auger-dominated carrier recombination and relaxation dynamics within cdse-based nanoplatelets” in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Electrical Engineering.

An abstract for Yana’s dissertation is included below.

Examinations are open to all members of the campus community as well as the general public. Registration is not required for in-person defences.

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ABSTRACT

Two-dimensional colloidal semiconductor nano-materials, i.e., the family of II-VI compound semiconductors, most commonly cadmium selenide, have attracted a significant amount of attention owing to their unique optical properties. Currently, they are considered a promising material system for opto-electronic device applications. It is widely recognized that carrier recombination and relaxation dynamics play an important role in shaping the properties of a particular semiconductor. A detailed understanding of the carrier dynamics is an essential requirement for being able to predict the device potential of material in question. The objective of this thesis is to explore the Auger effect on the carrier recombination and relaxation dynamics within the multi-exciton regime within colloidally synthesized bare cadmium selenide nanoplatelets and cadmium selenide/cadmium sulfide core/shell hetero-structured nanoplatelets. The carrier decay dynamics within such nanoplatelets are analyzed through an inversion analysis method with a bi-molecular recombination rate equation, which shows good description of the bi-excitonic Auger recombination process, the carrier decay transient being converted back into a rate of change with respect to time. Various approaches are employed to smooth the experimental data in order to manage the amplified noise presented during the numerical differentiation process. The relationship between the average number of excitons per NPL and the carrier temperature is also established. Based on this fundamental relation, the effect of the Auger re-heating on the carrier relaxation dynamics is then studied.

From this analysis, it is demonstrated that, in the multi-exciton regime, the Auger effect plays a dominant role in the recombination dynamics within cadmium selenide-based nanoplatelets, and that it is effectively suppressed through engineering a core/shell hetero-structure. This effect also dominates the carrier relaxation dynamics after the initial rapid cooling within such nanoplatelets. The results obtained here have the potential to provide broader insight into carrier recombination and relaxation over a wide array of two-dimensional nano-structures. The basic understanding of their behaviors is helpful for the application of these materials.