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.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.