title: Understanding of sub-band gap absorption of femtosecond-laser sulfur hyperdoped silicon using synchrotron-based techniques.
abstract: The correlation between sub-band gap absorption and the chemical states and electronic and atomic structures of S-hyperdoped Si have been extensively studied, using synchrotron-based x-ray photoelectron spectroscopy (XPS), x-ray absorption near-edge spectroscopy (XANES), extended x-ray absorption fine structure (EXAFS), valence-band photoemission spectroscopy (VB-PES) and first-principles calculation. S 2p XPS spectra reveal that the S-hyperdoped Si with the greatest (~87%) sub-band gap absorption contains the highest concentration of S(2-) (monosulfide) species. Annealing S-hyperdoped Si reduces the sub-band gap absorptance and the concentration of S(2-) species, but significantly increases the concentration of larger S clusters [polysulfides (Sn(2-), n > 2)]. The Si K-edge XANES spectra show that S hyperdoping in Si increases (decreased) the occupied (unoccupied) electronic density of states at/above the conduction-band-minimum. VB-PES spectra evidently reveal that the S-dopants not only form an impurity band deep within the band gap, giving rise to the sub-band gap absorption, but also cause the insulator-to-metal transition in S-hyperdoped Si samples. Based on the experimental results and the calculations by density functional theory, the chemical state of the S species and the formation of the S-dopant states in the band gap of Si are critical in determining the sub-band gap absorptance of hyperdoped Si samples.
authors.affiliation: 1] Department of Physics, Tamkang University, Tamsui 251, Taiwan [2] Department of Physics, Indian Institute of Science Education and Research, Bhopal 462066, India.
authors.forename: Mukta V
authors.initials: MV
authors.lastname: Limaye
authors.affiliation: Department of Physics, Tamkang University, Tamsui 251, Taiwan.
authors.forename: S C
authors.initials: SC
authors.lastname: Chen
authors.affiliation: Department of Physics, Tamkang University, Tamsui 251, Taiwan.
authors.forename: C Y
authors.initials: CY
authors.lastname: Lee
authors.affiliation: Department of Physics, Tamkang University, Tamsui 251, Taiwan.
authors.forename: L Y
authors.initials: LY
authors.lastname: Chen
authors.affiliation: 1] Department of Physics, Tamkang University, Tamsui 251, Taiwan [2] Department of Physics, Indian Institute of Science Education and Research, Bhopal 462066, India.
authors.forename: Shashi B
authors.initials: SB
authors.lastname: Singh
authors.affiliation: Department of Physics, Tamkang University, Tamsui 251, Taiwan.
authors.forename: Y C
authors.initials: YC
authors.lastname: Shao
authors.affiliation: Department of Physics, Tamkang University, Tamsui 251, Taiwan.
authors.forename: Y F
authors.initials: YF
authors.lastname: Wang
authors.affiliation: Department of Physics, Tamkang University, Tamsui 251, Taiwan.
authors.forename: S H
authors.initials: SH
authors.lastname: Hsieh
authors.affiliation: Department of Physics, Tamkang University, Tamsui 251, Taiwan.
authors.forename: H C
authors.initials: HC
authors.lastname: Hsueh
authors.affiliation: Department of Applied Physics, National University of Kaohsiung, Kaohsiung 811, Taiwan.
authors.forename: J W
authors.initials: JW
authors.lastname: Chiou
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
authors.forename: C H
authors.initials: CH
authors.lastname: Chen
authors.affiliation: National Synchrotron Radiation Research Center, Hsinchu 300, Taiwan.
authors.forename: L Y
authors.initials: LY
authors.lastname: Jang
authors.affiliation: Department of Physics, National Dong Hwa University, Hualien 974, Taiwan.
authors.forename: C L
authors.initials: CL
authors.lastname: Cheng
authors.affiliation: Department of Physics, Tamkang University, Tamsui 251, Taiwan.
authors.forename: W F
authors.initials: WF
authors.lastname: Pong
authors.affiliation: Canadian Light Source Inc., Saskatoon SK S7N OX4, Canada.
authors.forename: Y F
authors.initials: YF
authors.lastname: Hu