Progress toward Producing n-Type CdSe Quantum Dots: Tin and Indium Doped CdSe Quantum Dots

Controlling conductivity via doping in semiconductor quantum dots is an important part of nanoparticle research. In this report, doping of CdSe quantum dots with indium and tin is explored. High-resolution nanoprobing confirms the presence of indium and tin in the particles and the inclusion of indium into the particles without forming a separate phase. The tin doped CdSe samples show preferential adsorption of tin in quantum dots from the solution during synthesis while incorporation of indium is somewhat statistical. In agreement with the expected n-type behavior, the photoluminescence (PL) of both indium and tin doped samples exhibits a significantly steeper temperature dependence, compared to undoped CdSe quantum dots. Comparison of theory and experimental data suggests that the approximate locations of the dopants levels are at 280 and 100 meV below the conduction band edge of the indium and tin doped quantum dots, respectively. The relative temperature dependent Stokes shifts of the doped samples are larger than those of the undoped sample, suggesting that the electron is backfilling the lowest unoccupied quantum dots levels. The oxidized doped samples exhibit increased polarized band-edge emission. The likely explanation of the polarized emission is that trapping times are fast in the oxidized doped samples compared to the undoped samples.