Revisiting the Dependence of the Optical and Mobility Gaps of Hydrogenated Amorphous Silicon on Hydrogen Concentration

Legesse, Merid; Nolan, Michael; Fagas, Giorgos

doi:10.1021/jp408414f

Cited by 26 publications

(22 citation statements)

References 48 publications

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“…By contrast, later studies [17][18][19][20][21][22][23] generally claimed that the optical gap of a-Si:H is dependent on H concentration, even though some of 5 them [18 -21] showed that a constant optical gap is achieved at saturation. Our previous work [14] showed for the first time that the optical and mobility gaps of a-Si:H are invariant with H content as long as H saturation is reached.…”

Section: Introductionmentioning

confidence: 89%

“…we examined H contents of 14%, 15 % and 16.5 % [14] and in this work, we focus on saturation H content of 14 %. This saturated model structure of a-Si:H is relaxed with GGA-DFT.…”

Section: Methods and Preparationmentioning

confidence: 99%

“…Fig. 5 shows the Tauc plot from which we obtain the optical band gap of undersaturated a-Si:H with different H content [14]. We fit the linear part of each plot with a linear function and extrapolation of this function allows us to obtain the optical gap of each aSi:H sample.…”

Section: Fig 3 Vibrational Density Of States For Bulk A-si and A-simentioning

confidence: 99%

“…However, in a grown a-Si:H film, an increase in the hydrogen content can be associated with a higher degree of disorder [13]. H concentration also strongly influences the fundamental optical and mobility gaps in aSi:H [14]. The importance of short and long Si-Si bonds has recently been discussed in the context of the band tail and mid-gap states in a-Si:H [15][16][17][18][19][20].…”

Section: Introductionmentioning

confidence: 99%

“…The dependence of the optical gap of aSi:H on H content, up to saturation, has been well studied [14,[21][22][23][24][25][26][27]. To summarise, Cody et al [27] showed that the optical gap of a-Si:H films, Eopt, is independent of the H concentration, so long as H saturation is achieved.…”

Section: Introductionmentioning

confidence: 99%

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A first principles analysis of the effect of hydrogen concentration in hydrogenated amorphous silicon on the formation of strained Si-Si bonds and the optical and mobility gaps

Legesse

Nolan

Fagas

2014

Journal of Applied Physics

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Original citationLegesse, M., Nolan, M. and Fagas, G. (2014) ' AbstractIn this paper we use a model of hydrogenated amorphous silicon generated from molecular dynamics with density functional theory calculations to examine how the atomic geometry and the optical and mobility gaps are influenced by mild hydrogen oversaturation. The optical and mobility gaps show a volcano curve as the hydrogen content varies from undersaturation to mild oversaturation, with largest gaps obtained at the saturation hydrogen concentration.At the same time, mid-gap states associated with dangling bonds and strained Si-Si bonds disappear at saturation but reappear at mild oversaturation which is consistent with the evolution of optical gap. The distribution of Si-Si bond distances provides the key to the change in electronic properties. In the undersaturation regime the new electronic states in the gap arise from the presence of dangling bonds and strained Si-Si bonds, which are longer than the equilibrium Si-Si distance. Increasing hydrogen concentration up to saturation 2 reduces the strained bonds and removes dangling bonds. In the case of mild oversaturation the mid-gap states arise exclusively from an increase in the density of strained Si-Si bonds.Analysis of our structure shows that the extra hydrogen atoms form a bridge between neighbouring silicon atoms, thus increasing the Si-Si distance and increasing disorder in the sample.3

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Section: Introductionmentioning

confidence: 89%

“…we examined H contents of 14%, 15 % and 16.5 % [14] and in this work, we focus on saturation H content of 14 %. This saturated model structure of a-Si:H is relaxed with GGA-DFT.…”

Section: Methods and Preparationmentioning

confidence: 99%

Section: Fig 3 Vibrational Density Of States For Bulk A-si and A-simentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

A first principles analysis of the effect of hydrogen concentration in hydrogenated amorphous silicon on the formation of strained Si-Si bonds and the optical and mobility gaps

Legesse

Nolan

Fagas

2014

Journal of Applied Physics

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Improved Photoactivity of Pyroxene Silicates by Cation Substitutions

et al. 2018

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We investigated the possibility of band structure engineering of pyroxene silicates with chemical formula A B Si O by proper cation substitution. Typically, band gaps of naturally formed pyroxene silicates such as NaAlSi O are quite high (≈5 eV). Therefore, it is important to find a way to reduce band gaps for these materials below 3 eV to make them usable for optoelectronic applications operating at visible light range of the spectrum. Using first-principles calculations, we found that appropriate substitutions of both A and B cations can reduce the band gaps of these materials to as low as 1.31 eV. We also discuss how the band gap in this class of materials is affected by cation radii, electronegativity of constituent elements, spin-orbit coupling, and structural modifications. In particular, the replacement of Al in NaAlSi O by another trivalent cation Tl results in the largest band-gap reduction and emergence of intermediate bands. We also found that all considered materials are still thermodynamically stable. This work provides a design approach for new environmentally benign and abundant materials for use in photovoltaics and optoelectronic devices.

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A Spin‐Encoded All‐Dielectric Metahologram for Visible Light

Ansari

Kim

Lee

et al. 2019

Laser & Photonics Reviews

120

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Dielectric materials that are low‐loss in the visible spectrum provide a promising platform to realize the pragmatic features of metasurfaces. Here, all‐dielectric, highly efficient, spin‐encoded transmission‐type metaholograms (in the visible domain) are demonstrated by utilizing hydrogenated amorphous silicon (a‐Si:H). In comparison to previously reported visible metaholograms based on TiO2 and other dielectric materials, all‐dielectric metasurfaces provide a cost‐effective more straightforwardly fabricated (aspect ratio 4.7), CMOS compatible, and comparably efficient solution in the visible domain. A unique way of utilizing polarization as an extra degree of freedom in the design to implement transmission‐type helicity‐encoded metaholograms is also proposed. The produced images exhibit high fidelity under both right and left circularly polarized illuminations. The proposed cost‐effective and CMOS‐compatible material and methods open up an avenue for on‐chip development of numerous new phenomena with high efficiency in the visible domain.

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Revisiting the Dependence of the Optical and Mobility Gaps of Hydrogenated Amorphous Silicon on Hydrogen Concentration

Cited by 26 publications

References 48 publications

A first principles analysis of the effect of hydrogen concentration in hydrogenated amorphous silicon on the formation of strained Si-Si bonds and the optical and mobility gaps

A first principles analysis of the effect of hydrogen concentration in hydrogenated amorphous silicon on the formation of strained Si-Si bonds and the optical and mobility gaps

Improved Photoactivity of Pyroxene Silicates by Cation Substitutions

A Spin‐Encoded All‐Dielectric Metahologram for Visible Light

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