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 S2− (monosulfide) species. Annealing S-hyperdoped Si reduces the sub-band gap absorptance and the concentration of S2− species, but significantly increases the concentration of larger S clusters [polysulfides (Sn2−, 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.
Highlights
At high temperatures responsible for the reactivation
An Si L3,2 x-ray emission spectroscopic (XES) study of S-doped Si samples [up to 0.7 atomic percentage]9 exhibited induced emission feature intensity above the Si valence-band-maximum (EVBM), which scaled linearly with S concentration associated with the S-dopant, and the line-shape of the S-dopant feature changed across the insulator-to-metal transition (IMT)
Density Function Theory (DFT) suggested that the chalcogen-induced IMT arises from the merging of dopant states and conduction bands in chalcogens hyperdoped Si4,5,11
Summary
The 500 Torr sample has an average IR absorptance of ~87%, but annealing at 500 °C reduces the average IR absorptance to ~23% and annealing at 700 °C reduce it further to ~7% Both the Si K-edge XANES and EXAFS results showed that the sample annealed at the high temperature of 700 °C and the undoped Si(100) reference have similar near-edge absorption feature and structural ordering, illustrating that the sub-band gap absorption of the S-hyperdoped Si samples is clearly related to their electronic states and atomic structural ordering, which are influenced by the concentration of S-dopant and thermal annealing. Our theoretical calculations based on the DFT method are consistent with experimental results and the IMT of S-doped Si is predicted to occur at an S concentration at a critical value of 0.46% (~2.3 × 1020 cm−3)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: 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.
