InAs Band-Edge Exciton Fine Structure
MIT Lincoln Laboratory Lexington United States
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Semiconductor nanocrystals rarely, if ever, exhibit emission linewidths which are lifetime-limited. Instead, there are a number of linewidth broadening mechanisms which are relevant under various conditions, such as spectral diffusion, charging, and excitonic fine structure. While spectral diffusion and charging are most likely photoinduced effects and thus can be modulated by the excitation rate of the nanocrystals, fine-structure broadening is fundamental to the photophysics of nanocrystals and most likely unavoidable. A complete understanding of the excitonic energy landscape enables us to determine dephasing rates, linewidths, lifetimes, and other parameters essential to optical applications. Here we discuss the relationship between the excitonicfine structure and the emission dynamics of InAsCdS coreshell nanocrystals. At room temperature wefind steady-state emission dynamics on order of 150 ns, and as the temperature is lowered wefind that the relaxation is greatly slowed 19 s at 36K. Wefind that these emission dynamics are well-explained by a band-edge model including a pair of dark and bright excitonic states, separated in energy by 23 meV.