First-Principles Study of the Structural, Electronic, and Optical Properties of Oxide-Sheathed Silicon Nanowires

Abstract

Using a density functional theory approach, we examine the dielectric function (ε(ω)) optical spectra and electronic structure of various silicon nanowire (SiNW) orientations (<100>, <110>, <111>, and <112>) with amorphous oxide sheaths (-a-SiOx) and compare the results against H-terminated reference SiNWs. We extend the same methods to investigate the effects of surface passivation on <111> SiNW properties using functional group termination (-H, -OH, and -F) and three different thicknesses of oxide sheath passivation. Oxide layer growth is evidenced in the spectra by concomitant appearance of tail oxide character with signatures of increased Si disorder. Suboxide contributions and increased Si disorder from oxidation average out the band structure dispersion observed in the reference SiNWs. Furthermore, we plot average Seraphin coefficients for <111> passivations that clearly distinguish functional group termination from surface oxidation and discuss the suboxide and disorder contributions on the characteristic intersection of these coefficients. The substantial difference in properties observed between <111>-OH and <111>-a-SiOx SiNWs emphasizes the importance of using realistic oxidation models to improve understanding of SiNW properties.

Direct and indirect band gaps in Ge under biaxial tensile strain investigated by photoluminescence and photoreflectance studies

“…) of the refractive index are calculated from the real (ε 1 ) and imaginary (ε 2 ) parts of ε m , [32] the Seraphin-Bottka coefficients α and β can be obtained from the relations [33,34]:…”

“…In previous works, these relations between the SeraphinBottka coefficients and ε m have been used by Sundari and Raghavan [34] to evaluate the degree of disorder present in experimental samples of tetrahedrally bonded semiconductors, and by Bondi et al [33] to assess the contribution to optical spectra of suboxide composition and bonding disorder in oxide terminated Si nanowires. In this work, they provide a convenient way to extract parameters for experimental photoreflectance spectra, starting only from plane-wave pseudopotential DFT calculations.…”

Two-Dimensional Hydrous Silica: Nanosheets and Nanotubes Predicted from First-Principles Simulations

“…8 Zhao and co-workers studied anhydrous silica sheets and related tubes using first-principles calculations, 21 whereas De Leeuw and co-workers investigated hydration effects on anhydrous silica tubes. [24][25][26][27] To the best of our knowledge, to date theoretical studies on 2D hydrous silica sheets have not yet been reported. [24][25][26][27] To the best of our knowledge, to date theoretical studies on 2D hydrous silica sheets have not yet been reported.…”

Fluorination Effects on the Structural Stability and Electronic Properties of sp3-type Silicon Nanotubes

“…Furthermore, the identity of the halogen atom was found to impact the resulting bandgap of the system where larger halogen atoms resulted in more pronounced effect on the bandgap. Bondi et al 53 have shown that for SiNWs grown along the [111] orientation, fluorine surface decoration results in increased band density. Studying the effects of crystallographic orientation, Ng et al 61 were found to strongly decrease with respect to the fully hydrogenated counterparts.0 F ⊥ Going beyond SiNW structures, we have recently presented a computational study exploring the structural and electronic properties of fully hydrogenated sp 3 -type silicon nanotubes (SiNTs) grown along various crystallographic directions.…”