Dresden 2011 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 91: Joint Focussed Session: Theory and Computation of Electronic Structure: New Frontiers VIII
HL 91.4: Talk
Friday, March 18, 2011, 12:15–12:30, TRE Phy
Impact ionization rates from ab initio calculations — •Marton Voros1, Dario Rocca2, Gergely Zimanyi3, Giulia Galli2,3, and Adam Gali1,4 — 1Budapest University of Technology and Economics, Department of Atomic Physics — 2UC Davis, Department of Chemistry — 3UC Davis, Department of Physics — 4Hungarian Academy of Sciences, Research Institute of Solid State Physics and Optics
Achieving multi exciton generation (MEG) in semiconducting nanocrystals may lead to overcome the well-known Shockley-Queisser limit when building semiconductor-based solar cells. A thourough, theoretical understanding of the experiments that reported MEG in e.g. Si and PbSe nanocrystals, is still missing and could significantly contribute to clarify the several controversial results in the field. Several theoretical and numerical studies have addressed the origin of the MEG formation, mostly supporting an impact ionization mechanism. However, impact ionization rates have only been evaluated for model nanocrystals by using empirical pseudopotentials fitted to bulk properties or by applying tight binding wavefunctions, and model dielectric functions to describe the screened Coulomb interaction. We present a full ab-initio scheme based on Density Functional Theory in a plane-wave pseudopotential implementation that includes static screening within the random-phase approximation. As a first application, we will discuss how impact ionization rates are affected by the size of small Si nanocrystals.