Journal
PHYSICA STATUS SOLIDI B-BASIC SOLID STATE PHYSICS
Volume 258, Issue 7, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/pssb.202000623
Keywords
boron doping; nanocrystals; quantum dots; silicon
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Funding
- Alexander von Humboldt Foundation
- German Research Foundation DFG [HI 1779/3-1]
- 2018 Theodore-von-Karman Fellowship of RWTH Aachen University, Germany
- Projekt DEAL
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The study found that the inability to efficiently insert boron into Si nanovolumes is a fundamental obstacle for electronic doping of ultra-small Si nanostructures.
Doping of silicon nanostructures is crucial to understand their properties and to enhance their potential in various fields of application. Herein, SiO2-embedded Si nanocrystals (quantum dots) approximate to 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 1s (K shell) electron binding energies of B in 11 different, thermodynamically stable configurations of the Si/SiOx/SiO2 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 SiO2 matrix and near the Si-nanocrystal/SiO2 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.
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