Doping is used to control free carrier type and concentration in semiconductor materials. In bulk semiconductors, doping is conventionally achieved through impurity substitution, and less well-known, by controlling a material’s stoichiometry. However, doping in low-dimensional, colloidal semiconductors presents both new opportunities and challenges. The electron and hole concentrations in colloidal nanocrystal (NC) and nanowire (NW) assemblies have often been manipulated by “remote doping,” exploiting the large surface-to-volume ratio of nanostructures to add atoms, ions, or ligands to the surface that serve as dopants. For example, we describe methods of 1) thermal evaporation and diffusion and 2) wet-chemical techniques to introduce extrinsic impurities to and non-stoichiometry through the nanostructure surface to passivate surface traps and dope NC and NW assemblies. However, the doping efficiency of colloidal nanostructures is often extremely low, such that only 1% of dopants yield carriers. These low doping efficiencies are consistent with increased ionization energies from quantum and dielectric confinement effects. We show for a given size nanostructure, where quantum confinement effects are fixed, the doping efficiency can be enhanced by &gt;10-fold by encapsulating the NCs and NWs in high dielectric constant materials that reduce the dielectric mismatch between the nanostructure and its surroundings. We give examples where n- and p-type semiconductor NC and NW assemblies are used to construct flexible, electronic transistors and integrated circuits and optoelectronic solar photovoltaics and photodetectors.

N- and P-doping of colloidal nanocrystal and nanowire assemblies

256th National Meeting (2018)

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