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TT: Fachverband Tiefe Temperaturen

TT 91: Focus Session: Frontiers of Electronic Structure Theory - Non-Equilibrium Phenomena at the Nano-Scale VI (organized by O)

TT 91.2: Vortrag

Donnerstag, 3. April 2014, 11:00–11:15, TRE Ma

Multiple Exciton Generation in Si and Ge Nanoparticles with high pressure core structures — •Stefan Wippermann¹, Marton Vörös², Dario Rocca³, Adam Gali⁴, Gergely Zimanyi², and Giulia Galli² — ¹Max-Planck-Institute for Iron Research, Düsseldorf — ²University of California, Davis — ³Universite de Lorraine, Nancy — ⁴Budapest University of Technology and Economics

Multiple exciton generation (MEG) in semiconductor nanoparticles (NPs) is a promising path towards surpassing the Shockley-Queisser limit in solar energy conversion efficiency. Recent studies demonstrate MEG to be more efficient in NPs than in the bulk, including Si. However, the increased efficiency is observed only on a relative energy scale in units of the gap: quantum confinement (QC) effects believed to be responsible for efficient MEG in NPs, also increase their optical gap, swiftly shifting the MEG threshold beyond the solar spectrum.

We present density functional and many body perturbation theory calculations of the electronic, optical, and impact ionization properties of Si and Ge nanoparticles (NPs) with core structures based on high-pressure bulk Si and Ge phases. Si and Ge particles with a BC8 or ST12 core structure exhibit significantly lower optical gaps and multiple exciton generation (MEG) thresholds, and an order of magnitude higher MEG rate than diamondlike ones of the same size (1).

(1) S. Wippermann et al., Phys. Rev. Lett. 110, 046804 (2013)