Theory of Quantum Plasmon Resonances in Doped Semiconductor Nanocrystals

Doped semiconductor nanocrystals represent a new type of quantum plasmonic material with optical resonances in the infrared. These nanocrystals are fundamentally different from the metal nanoparticles because the electron density in a semiconductor can be tuned over a wide interval. Using the DFT-based time-dependent formalism, we computed the absorption spectra of doped quantum dots as a function of the number of carriers in the dot. The dynamic properties of doped quantum dots undergo an interesting transition from the size-quantization regime to the classical regime of plasmon oscillations. We demonstrated this quantum-to-classical transition for both self-doped copper chalcogenide dots and impurity-doped II-VI nanocrystals. We also showed that the plasmon frequency and electron density in the dot depend on the type of doping, which can be bulk-like or surface-like. The results obtained in this study can be used to predict and describe optical properties of a variety of semiconductor nanocrystals with quantum plasmonic resonances.