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 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.

Influence of chromium hyperdoping on the electronic structure of CH3NH3PbI3 perovskite: a first-principles insight

“…Thus, there would be no mixing between IGB and CB, i.e ., the existence of a gap between the IGB and the CB. In addition, several works have demonstrated the formation of an IGB, whose energy differences with the conduction band are ≈0.25 eV 77 – 79 . In a similar way as in the PBEsol calculation, three flat bands are also noted in the valence band maximum, which should also be due to Cr atoms.…”

Understanding the structural transformation, stability of medium-sized neutral and charged silicon clusters

“…The experimental and theoretical studies of the atomic and molecular clusters are interesting topics since they constitute intermediate phases between individual atoms and bulk solids, which can be used to understand how the fundamental properties of materials evolve from isolated atoms or small molecules to a bulk phase 1 2 3 4 5 6 7 8 . The study of small clusters can help us to design better nanosystems with specific physical and chemical properties.…”

Infinitesimal sulfur fusion yields quasi-metallic bulk silicon for stable and fast energy storage

“…4 and 5) (ref. 2 ). In addition, electron energy loss spectroscopy (EELS) indicates that the QMS contains sulfur in various states other than elemental sulfur, and the Si L-edge of the QMS shifts upward from 99.4 to 99.9 eV, resulting from the sulfur that fuses into the Si in two separate manners ( Fig.…”

“…hen silicon (Si) is heavily doped with chalcogen family elements (e.g., S, Se, and Te) at a concentration exceeding the equilibrium solid solubility, it experiences the insulator-to-metal transition (IMT); thus, it shows great potential for optoelectronic applications such as infrared detection and intermediate-band solar cells 1,2 . At present, such a supersaturated structure has been exclusively realized by an intricate combination of ion implantation, pulsed-laser-induced melting, and rapid solidification to activate the dopants and restore the lattice damaged by accelerated ions 3 .…”