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Wenjie Yang1 Naheed Ferdous2 Philippe Chow3 James Gaudet4 Peter Simpson4 Austin Akey5 Jeffrey Warrender3 Michael Aziz5 Elif Ertekin2 Jim Williams1

1, Australian National University, Canberra, Australian Capital Territory, Australia
2, University of Illinois at Urbana-Champaign, Champaign, Illinois, United States
3, U.S. Army ARDEC- Benet Laboratories, Watervliet, New York, United States
4, University of Western Ontario, London, Ontario, Canada
5, Harvard University, Cambridge, Massachusetts, United States

Ion implantation followed by pulsed laser melting can produce hyperdoped Si with a highly non-equilibrium impurity concentration, giving rise to sub-band gap optical absorption that holds potential in Si-based photovoltaics and infrared light detection. [1, 2] In particular, a Si-based infrared photodetector has been successfully demonstrated on Au-hyperdoped Si, motivating a detailed study onnthe role of substitutional Au and other related defect complexes that arise from the non-equilibrium hyperdoping process. [3]

In this study, the atomic location of Au in hyperdoped Si is determined using Rutherford backscattering spectrometry combined with ion channelling (RBS/C) and triangulated angular scans. Additionally, the local lattice environment around the Au atoms is examined using a combination of techniques,includinghigh-resolution transmission electron microscopy (HRTEM), high-resolution x-ray diffraction (HRXRD)and positron annihilation spectroscopy (PAS). Surprisingly,the incorporation of large Au atoms into the Si lattice appears to contract rather than expand the lattice. We show that vacanciesare trapped following pulsed laser melting, and, with the aid of density functional theory (DFT) calculations, propose that the vacancy trapping process is consistent with the local minimisation of lattice strain around the large Au atoms. Finally, we explore the thermal stability and sub-band gap optical activity of these vacancy-type defects. This vacancy trapping process may be global in other laser-melted hyperdoped Si systems with large-size impurities and may affect their efficacy as infrared absorbers.

References:
[1] J. M., Warrender, Applied Physics Reviews, 3(3) (2016)
[2]W. Yang, J. Mathews, and J. S. Williams, Materials Science in Semiconductor Processing, 62, (2017)
[3] J. P. Mailoa, et al., Nature Communications, 5:3011 (2014)

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