UC Berkeley

Semiconductor nanostructures are a class of materials that have many attractive properties for optoelectronic applications and incorporation into solid-state devices. Compared to bulk semiconductors, they offer discrete, tunable electronic energy levels and an enhancement of many charge carrier interactions. Improving our understanding of the charge dynamics in these materials and how their behavior fundamentally differs from bulk solids will be crucial for ongoing and future development of semiconductor nanostructure devices. In this dissertation, the use of single particle spectroscopy to probe charge carrier dynamics in semiconductor nanostructures is described.

The first introductory chapter provides an overview of some elementary background knowledge regarding the unique electronic structure of confined semiconductors and how this results in their distinct carrier dynamics. The advantages of single particle experiments are discussed as well as the detection methods available to obtain a sufficiently high signal-to-noise ratio, focusing primarily on the photoluminescence (PL) detection of a single optically excited particle. Finally, PL blinking in single semiconductor nanocrystals (NCs) is introduced and the leading theories proposed to account for the phenomenon are summarized. The second chapter details an experimental setup optimized for studying the PL emission from single particles, including an ultrafast, tunable laser system as the excitation source, a confocal microscope to obtain a small focal volume for single particle excitation, and the detection and acquisition components, namely sensitive photodiodes and time-correlated single photon counting techniques.

The subsequent three chapters present results from a range of semiconductor nano-materials. The third and fourth chapters focus on PL blinking in semiconductor NCs, beginning with the use of PL blinking results in thick-shell CdSe/CdS chalcogenide NCs to compare the effectiveness of two distinct analysis methods for probing multi-level emission. Extending to lead halide CsPbBr₃ perovskite NCs, PL blinking is investigated to understand how charge trapping in these newly available compositions compares to traditional chalcogenide NCs. The next chapter provides three condensed summaries of PL studies in semiconductor nanowires (NWs). Time-resolved PL experiments of colloidal CsPbX₃ (X = Cl, Br, I) NWs and InP NWs are detailed, and a spectroscopic study of stimulated emission in isolated CsPbBr₃ NWs is described. Finally, the last chapter offers concluding remarks of the dissertation as well as a glimpse into the possible future directions of the laboratory.