Proceedings of nanoGe Fall Meeting 2018 (NFM18)
DOI: https://doi.org/10.29363/nanoge.nfm.2018.346
Publication date: 6th July 2018
Cadmium chalcogenide (CdX, X=Se, S, Te) colloidal quantum wells or nanoplatelet (NPLs) have atomically precise thickness of a few CdX layers (1-2 nm) and uniform exciton confinement energy across lateral dimensions of 10s of nanometer and larger. This unique property has led to speculation of coherent delocalization of the exciton center-of-mass over the entire NPL, which would have profound effect on fundamental properties of excitons (including its oscillator, transport mechanism and Auger annihilation) and their applications (such as lasing threshold). In this talk, I will summarize a series of recent studies on fundamental exciton properties in 2D NPLs. We show that at room temperature, exciton transport can be described by 2D diffusion with diffusion constants near the bulk crystal values and hot exciton diffusion completes with exciton relaxation. In CdSe NPLs, the biexciton Auger recombination lifetime does not depend linear on its volume, deviating from the “Universal Volume” scaling law that has been reported for 0D quantum dots. Instead, the Auger lifetime scales linearly with the lateral size because of the size dependent collision frequency, and the Auger lifetime depends sensitively (nonlinearly) on the NPL thickness due to change in the degree of quantum confinement. We suggest Auger lifetime in for other 2D NPLs and 1D nanorods can also be expected to deviate from the volume scaling law because of the different dependences on the quantum confined and non-confined dimensions. We have developed an optical gain model that accounts for the nature of 1D confinement in NPLs and revealed the origin of low gain thresholds in these materials. Finally, we will also discuss conditions under which coherent delocalization of excitons and the Giant Oscillator Strength Transition (GOST) effect can be observed.
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