Minimum Line Width of Surface Plasmon Resonance in Doped ZnO Nanocrystals

The optical response of ZnO nanocrystals (NCs) doped with Al (Ga) impurities is calculated using a model that incorporates the effects of quantum confinement, dielectric mismatch, surface, and ionized impurity scattering. For dopant concentrations of a few percent, the NC polarizability is dominated by a localized surface plasmon resonance (LSPR) in the infrared (IR) which follows the Drude-Lorentz law for NC diameter above ∼10 nm but is strongly blue-shifted for smaller diameters due to quantum confinement effects. The intrinsic width of the LSPR peak is calculated in order to characterize plasmon losses induced by ionized impurity scattering. Widths below 80 meV are found in the best cases, in agreement with the lowest values recently measured on single NCs. These results confirm that doped ZnO NCs are very promising for the development of IR plasmonics. The width of the LSPR peak strongly increases when dopants are placed near the surface of the NCs or when additional fixed charges are present.