Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology. Department of Mechanical Engineering, Mailoa, Jonathan P, Johnson, Benjamin C, Buonassisi, Anthony, Yang, W., Akey, A. J., Smillie, L. A., McCallum, J. C., Macdonald, D., Aziz, M. J., Williams, J. S., Massachusetts Institute of Technology. Department of Electrical Engineering and Computer Science, Massachusetts Institute of Technology. Department of Mechanical Engineering, Mailoa, Jonathan P, Johnson, Benjamin C, Buonassisi, Anthony, Yang, W., Akey, A. J., Smillie, L. A., McCallum, J. C., Macdonald, D., Aziz, M. J., and Williams, J. S.
Au-hyperdoped Si, synthesized by ion implantation and pulsed laser melting, is known to exhibit a strong sub-band gap photoresponse that scales monotonically with the Au concentration. However, there is thought to be a limit to this behavior since ultrahigh Au concentrations (> 1 × 10[superscript 20] cm[superscript −3]) are expected to induce cellular breakdown during the rapid resolidification of Si, a process that is associated with significant lateral impurity precipitation. This work shows that the cellular morphology observed in Au-hyperdoped Si differs from that in conventional, steady-state cellular breakdown. In particular, Rutherford backscattering spectrometry combined with channeling and transmission electron microscopy revealed an inhomogeneous Au distribution and a subsurface network of Au-rich filaments, within which the Au impurities largely reside on substitutional positions in the crystalline Si lattice, at concentrations as high as ∼ 3 at. %. The measured substitutional Au dose, regardless of the presence of Au-rich filaments, correlates strongly with the sub-band gap optical absorptance. Upon subsequent thermal treatment, the supersaturated Au forms precipitates, while the Au substitutionality and the sub-band gap optical absorption both decrease. These results offer insight into a metastable filamentary regime in Au-hyperdoped Si that has important implications for Si-based infrared optoelectronics., Australian Research Council (Grant LP160100981), United States. Army (Contract FA5209- 16-P-0104)