The Effect of Dielectric Environment on Doping Efficiency in Colloidal PbSe Nanostructures.

Doping, as a central strategy to control free carrier type and concentration in semiconductor materials, suffers from low efficiency at the nanoscale, especially in systems having high permittivity (ϵ) and large Bohr radii, such as lead chalcogenide nanocrystals (NCs) and nanowires (NWs). Here, we study dielectric confinement effects on the doping efficiency of lead chalcogenides nanostructures by integrating PbSe NWs in the platform of field effect transistors (FETs). Elemental Pb or In or elemental Se is deposited by thermal evaporation to remotely n- or p-dope the NWs. Polymeric and oxide materials of varying ϵ are subsequently deposited to control the dielectric environment surrounding the NWs. Analyzing the device characteristics, we extract the change of carrier concentration introduced by tailoring the dielectric environment. The calculated doping efficiency for n-type (Pb/In) and p-type (Se) dopants increases as the ϵ of the surrounding medium increases. Using a high-ϵ material, such as HfO for encapsulation, the doping efficiency can be enhanced by >10-fold. A theoretical model is built to describe the doping efficiency in PbSe NWs embedded in different dielectric environments, which agrees with our experimental data for both NW array and single NW devices. As dielectric confinement affects all low-dimensional materials, engineering the dielectric environment is a promising general approach to enhance doping concentrations, without introducing excess impurities that may scatter carriers, and is suitable for various device applications.