Tuning p-Type Transport in Bottom-Up-Engineered Nanocrystalline Pb Chalcogenides Using Alkali Metal Chalcogenides as Capping Ligands.

Abstract

Tuning the type and concentration of major carriers in semiconductor nanomaterials produced by the bottom-up assembly of colloidal nanocrystals (NCs) is a cornerstone for all solid-state device applications. A powerful strategy is to exploit the NCs high surface area to introduce the desired amount of dopants. Using PbS as a NC core material, various surface ligand-exchange strategies were investigated to incorporate controlled quantities of aliovalent electronic impurities. Alkali metal chalcogenides are used to replace the long-chain carboxylate ligand shell, followed by a thermal consolidation of NCs into dense nanostructured solids. A combined effect of adjusting the metal-to-chalcogen ratio with the diffusion of alkali ions into the cationic sublattice rendered a p-type conductivity with broadly adjustable carrier concentrations in the range of 1016-1019 cm-3. Such nanocrystalline solids hold great promise for applications such as thermoelectrics.