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On the Location of Boron in SiO 2 ‐Embedded Si Nanocrystals—An X‐ray Absorption Spectroscopy and Density Functional Theory Study
Author(s) -
Hiller Daniel,
König Dirk,
Nagel Peter,
Merz Michael,
Schuppler Stefan,
Smith Sean C.
Publication year - 2021
Publication title -
physica status solidi (b)
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.51
H-Index - 109
eISSN - 1521-3951
pISSN - 0370-1972
DOI - 10.1002/pssb.202000623
Subject(s) - dopant , xanes , materials science , nanocrystal , doping , density functional theory , boron , absorption spectroscopy , spectroscopy , silicon , absorption (acoustics) , electronic structure , chemical physics , quantum dot , nanotechnology , optoelectronics , chemistry , computational chemistry , optics , physics , organic chemistry , quantum mechanics , composite material
Doping of silicon nanostructures is crucial to understand their properties and to enhance their potential in various fields of application. Herein, SiO 2 ‐embedded Si nanocrystals (quantum dots) ≈3–6 nm in diameter are used as a model system to study the incorporation of B dopants by X‐ray absorption near‐edge spectroscopy (XANES). Such samples represent a model system for ultimately scaled, 3D‐confined Si nanovolumes. The analysis is complemented by real‐space density functional theory to calculate the 1 s (K shell) electron binding energies of B in 11 different, thermodynamically stable configurations of the Si/SiO x /SiO 2 system. Although no indications for a substitutional B‐acceptor configuration are found, the predominant O coordination of B indicates the preferred B incorporation into the SiO 2 matrix and near the Si‐nanocrystal/SiO 2 interface, which is inherently incompatible with charge carrier generation by dopants. It is concluded that B doping of ultrasmall Si nanostructures fails due to a lack of B incorporation onto Si lattice sites that cannot be overcome by increasing the B concentration. The inability to efficiently insert B into Si nanovolumes appears to be a boron‐specific fundamental obstacle for electronic doping (e.g., not observed for phosphorus) that adds to the established nanosize effects, namely, increased dopant activation and ionization energies.