Dresden 2017 – scientific programme
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HL: Fachverband Halbleiterphysik
HL 9: Quantum Dots: Preparation and Characterization
HL 9.3: Talk
Monday, March 20, 2017, 10:00–10:15, POT 112
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)