Extended X-ray absorption fine structure spectroscopy of selenium-hyperdoped silicon

Bonna K. Newman, Elif Ertekin, Joseph T. Sullivan, Mark T. Winkler, Matthew A. Marcus, Sirine C. Fakra, Meng Ju Sher, Eric Mazur, Jeffrey C. Grossman, Tonio Buonassisi

Research output: Contribution to journalArticlepeer-review

Abstract

Silicon doped with an atomic percent of chalcogens exhibits strong, uniform sub-bandgap optical absorptance and is of interest for photovoltaic and infrared detector applications. This sub-bandgap absorptance is reduced with subsequent thermal annealing indicative of a diffusion mediated chemical change. However, the precise atomistic origin of absorptance and its deactivation is unclear. Herein, we apply Se K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy to probe the chemical states of selenium dopants in selenium-hyperdoped silicon annealed to varying degrees. We observe a smooth and continuous selenium chemical state change with increased annealing temperature, highly correlated to the decrease in sub-bandgap optical absorptance. In samples exhibiting strong sub-bandgap absorptance, EXAFS analysis reveals that the atoms nearest to the Se atom are Si at distances consistent with length scales in energetically favorable Se substitutional-type point defect complexes as calculated by density functional theory. As the sub-bandgap absorptance increases, EXAFS data indicate an increase in the Se-Si bond distance. In specimens annealed at 1225 K exhibiting minimal sub-bandgap absorptance, fitting of the EXAFS spectra indicates that Se is predominantly in a silicon diselenide (SiSe2) precipitate state. The EXAFS study supports a model of highly optically absorbing point defects that precipitate during annealing into structures with no sub-bandgap absorptance.

Original languageEnglish (US)
Article number133507
JournalJournal of Applied Physics
Volume114
Issue number13
DOIs
StatePublished - Oct 7 2013

ASJC Scopus subject areas

  • Physics and Astronomy(all)

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