Atomistic Mechanisms for the Thermal Relaxation of Au -hyperdoped Si
Date
2019
Authors
Yang, Wenjie
Hudspeth, Quentin
Chow, Philippe K.
Warrender, Jeffrey M.
Ferdous, N.
Ertekin, E.
Malladi, G.
Akey, Austin J.
Aziz, Michael J.
Williams, James
Journal Title
Journal ISSN
Volume Title
Publisher
American Physical Society
Abstract
Au-hyperdoped Si produced by ion implantation and pulsed laser melting exhibits sub-band-gap absorption
in the near infrared, a property that is interesting for Si photonics. However, the sub-band-gap
absorption has previously been shown to be thermally metastable. In this work, we study the atomistic
processes that occur during the thermal relaxation of Au-hyperdoped Si. We show that the first step in
thermal relaxation is the release of substitutional Au from lattice sites. This process is characterized by
an activation energy of around 1.6 eV, a value similar to that associated with Au diffusion in Si, suggesting
that both processes could be rate limited by the exchange of substitutional and interstitial Au
atoms. As the system further relaxes, Au is found to locally diffuse and become trapped at nearby lattice
defects, notably vacancies and vacancy complexes. In fact, density-functional theory results suggest that
the formation of Au dimers is energetically favourable after the Au becomes locally trapped. The dimers
could subsequently evolve into trimers, etc., as other diffusing Au atoms become trapped at the dimer.
At low Au concentrations, this clustering process does not form visible precipitation after annealing at
750 ◦C for 3 min. In contrast, spherical Au precipitates are found in samples with higher Au concentrations
(>0.14 at. %), where the Au atoms and the associated lattice defect distributions are laterally
inhomogeneous.
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Source
Physical Review Applied
Type
Journal article
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Open Access
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DOI
10.1103/PhysRevApplied.12.024015