The role of surface defects in multi-exciton generation of lead selenide and silicon semiconductor quantum dots

The Journal of Chemical Physics
Heather M JaegerOleg V Prezhdo

Abstract

Multi-exciton generation (MEG), the creation of more than one electron-hole pair per photon absorbed, occurs for excitation energies greater than twice the bandgap (E(g)). Imperfections on the surface of quantum dots, in the form of atomic vacancies or incomplete surface passivation, lead to less than ideal efficiencies for MEG in semiconductor quantum dots. The energetic onset for MEG is computed with and without surface defects for nanocrystals, Pb(4)Se(4), Si(7), and Si(7)H(2). Modeling the correlated motion of two electrons across the bandgap requires a theoretical approach that incorporates many-body effects, such as post-Hartree-Fock quantum chemical methods. We use symmetry-adapted cluster with configuration interaction to study the excited states of nanocrystals and to determine the energetic threshold of MEG. Under laboratory conditions, lead selenide nanocrystals produce multi-excitons at excitation energies of 3 E(g), which is attributed to the large dielectric constant, small Coulomb interaction, and surface defects. In the absence of surface defects the MEG threshold is computed to be 2.6 E(g). For lead selenide nanocrystals with non-bonding selenium valence electrons, Pb(3)Se(4), the MEG threshold increases to 2.9...Continue Reading

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Citations

Jul 12, 2018·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Mahdi GordiHamidreza Ramezani
Jan 8, 2013·Journal of Chemical Theory and Computation·Daniel NeuhauserRoi Baer
Oct 8, 2013·Journal of Chemical Theory and Computation·Jennifer M Elward, Arindam Chakraborty

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Methods Mentioned

BETA
electron-electron scattering
electron scattering

Software Mentioned

GAUSSIAN
SAC

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