P-doping of Silicon Nanocrystals: Free Carriers vs. Defects (talk)

P-doping of Silicon Nanocrystals: Free Carriers vs. Defects — •DANIEL
HILLER1, JULIAN LOPEZ-VIDRIER1, SEBASTIAN GUTSCH1, MARGIT ZACHARIAS1, KEITA
NOMOTO2,3, and DIRK KÖNIG3 — 1Laboratory for Nanotechnology, IMTEK, University
of Freiburg, Germany — 2The University of Sydney, Australia — 3University of New
South Wales (UNSW), Sydney, Australia
We study the size limitations of conventional P-doping of ultra-small Si volumes
using Si nanocrystals (Si NCs) of 2-5 nm as a model system. Theoretical studies
predicted that P-doping of Si nanocrystals fails due to self-purification, increased
formation energies of substitutional P-atoms, and increased ionization energies of
donor electrons due to quantum- and dielectric confinement. However, several
groups reported a quenching of photoluminescence (PL) from Si NCs by P-doping
and attributed that to non-radiative Auger recombination with donor electrons. In
this work, we address this contradiction. We disprove the self-purification effect by
atom probe tomography (APT) measurements [1]. However, a correlation of
APT-statistics, PL- and I-V-measurements reveals that the PL quenching cannot be
explained by free carriers. X-ray absorption (XAS) measurements at the P-K-edge
indicate that the majority of P-atoms in Si NCs is not ionized at 300 K [3]. I-V
shows that P-ionization requires 100-500 meV depending on the NC size [2].
Using density functional theory (DFT) simulations [3], we explain the
PL-quenching by P-induced defect states.
[1] Phys. Status Solidi RRL (2016), DOI: 10.1002/pssr.201600376 [2] Appl. Phys.
Lett. 106, 113103 (2015) [3] Sci. Rep. 5, 09702 (2015)