Electronic structure and localized states in amorphous Si and hydrogenated amorphous Si

Meidanshahi, Reza Vatan; Bowden, Stuart; Goodnick, Stephen M.

doi:10.1039/c9cp01121h

Cited by 24 publications

(23 citation statements)

References 77 publications

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“…Therefore PCM measurements revealed that the origin of defect states might be a result of different type of general structural disorders beyond DBs. [15,16] In addition to experimental work, several recent theoretical and computational work have shown highly strained bonds significantly contributing to midgap states and DBs [17,18].…”

Section: B Defects In Amorphous Simentioning

confidence: 98%

See 1 more Smart Citation

From Femtoseconds to Gigaseconds: The SolDeg Platform for the Performance Degradation Analysis of Silicon Heterojunction Solar Cells

Unruh¹,

Meidanshahi²,

Hansen³

et al. 2020

Preprint

Self Cite

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Heterojunction Si solar cells exhibit notable performance degradation. This is a substantial challenge for their market acceptance and for basic science. In order to shed light to the underlying causes, we studied this problem by layering several techniques on top of each other in order to determine the dynamics of electronic defect generation. The first layer of our method is adapting LAMMPS Molecular Dynamics simulations to create aSi/cSi stacks. Our simulations use femtosecond time-steps. For the interatomic potential, we used the Artificial-Intelligence-based GAP interatomic potential. Next, we optimized these stacks with Density Functional calculations. This was followed by creating localized structural defects in the stacks by local heat blasting. We then analyzed the just-generated structural defects by the Inverse Participation Ratio (IPR) method to identify which structural defects induced and supported electronic defects. Next, we adapted the Nudged Elastic Band (NEB) method to determine the energy barriers that control the formation of these electronic defects. We performed the NEB method for thousands of electronic defects to determine the distributions of these energy barriers. Finally, we developed an Accelerated Superbasin Kinetic Monte Carlo approach to determine the time dependence of the electronic defect generation, as controlled by this energy barrier distribution. The determination of the energy barriers out to 4 eV enabled us to determine the defect generation out to Gigaseconds, or of the order of 10 years. Our method is thus capable of connecting physical processes from femtoseconds to Gigaseconds. Our main conclusions are that even in dark conditions, thermal activation processes lead to a substantial increase of the electronic defect density. Further, we also simulated the same processes at the accelerated testing temperature of 350K, and established a quantitative relationship between the regular and accelerated defect generation, thus making accelerated testing a more quantitative assessment tool.

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Section: B Defects In Amorphous Simentioning

confidence: 98%

“…Thus, the creation of accurate melt-quench a-Si requires significant DFT input. Even then, reaching experimental-level accuracy is still difficult, and this process can only yield structures on the edge of acceptability [18].…”

Section: A Creating the Amorphous/crystalline Stacks: Machine-learnin...mentioning

confidence: 99%

From Femtoseconds to Gigaseconds: The SolDeg Platform for the Performance Degradation Analysis of Silicon Heterojunction Solar Cells

Unruh¹,

Meidanshahi²,

Hansen³

et al. 2020

Preprint

Self Cite

View full text Add to dashboard Cite

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“…It is reported that in the strained Si network, the overal stain energy can be reduced by hydrogenation with commensurate reduction of mid-gap states and orbital localization. [17] H atom to a strained bond is associated with a change in the long range order, subsequently resulting in strain reduction and more stabilization. Increasing the structural order leads to strain release from the whole strained-Si structure with the replacement of weak strained Si-Si bonds by strong Si-Si bonds.…”

Section: -1 IV Characteristics Under the Mechanical Bending Stressmentioning

confidence: 99%

“…Also, the midgap state reduction can be from the replacement of relatively weak Si-Si bonds by strong Si-H bonds. [17] In strained poly-Si, the more strained bonds exist, the more bonds are going to be hydrogenated, where H is supplied from the PI substrate. And this comes to the reduction of midgap states and also the extracted Ntrap.…”

Section: -1 IV Characteristics Under the Mechanical Bending Stressmentioning

confidence: 99%

5‐2: Enhanced Bending Endurance with Transverse Tensile Strain and 4‐Terminal Double Gate LTPS TFTs for flexible AMOLED

Lee

Kang

et al. 2021

Symp Digest of Tech Papers

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This letter investigates the degradation behavior of p‐channel LTPS TFTs on PI substrate under the static bending stress. During 1hr bend, the threshold voltage shifts positively and the subthreshold slope increases slightly. In transverse compressive strain, the field effect mobility increases abruptly with the decrease of the effective channel length and the off state leakage current. This is attributed to the generation of the strain‐induced GI defects near the source and drain terminals, resulting in the trapping of electrons and a shrinkage of the effective channel length and the H passivation of the strained Si bonds in the channel. By inserting the bottom metal layer to block the H diffusion from PI substrate, the controllable normal NBTI behavior is observed in a strained LTPS TFT on PI. These transverse tensile strained and 4‐termianl double gate LTPS TFTs on PI shows as a stable switching TFTs on PI for the flexible system‐on‐panel display.

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“…Among various key factors to improve the performance, hydrogen concentration is one of the most relevant ones [8]. It has been shown that the hydrogenation of a-Si has a beneficial effect in reducing the overall strain energy of the a-Si network [9]. Legesse et al investigated the optical gap and the electron mobility with VASP [10] and proposed three regimes of the hydrogen concentration; in the unsaturated regime, both the optical gap and the mobility increase with the increase of hydrogen concentration until they converge to some constant values in the saturated regime.…”

Section: Introductionmentioning

confidence: 99%

Effects of Hydrogen Concentration and Cooling Speed on Fabrication of Hydrogenated Amorphous Silicon: Quantum Simulation

Li¹,

Matsumoto²

2021

IJTAN

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In order to investigate various properties of hydrogenated amorphous silicon (a-Si:H) for improvement of low conversion efficiency and stability of solar cells, a series of quantum simulations based on the density functional theory combined with the tight binding model were performed for a-Si:H with various hydrogen concentrations and cooling rates. The radial distribution function (RDF) for Si-Si pairs indicates that samples with higher H concentration (20% and 25%) give a structure in better agreement with experiments, but the RDF of Si-H pairs suggests that samples with lower H concentration (14%) may give more appropriate structure. The coordination number ( ) analysis indicates that more defects (dangling bonds and floating bonds) exist in 20% and 25% H concentration samples. Overall, a-Si:H with 14% H concentration gives most preferable structure. The cooling rate has also much effect on the structure. Sample with the slowest cooling rate is slightly more structured based on Si-Si pair RDF and . The electron transport of a-Si and a-Si:H were evaluated and the superiority of a-Si:H was confirmed.

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Electronic structure and localized states in amorphous Si and hydrogenated amorphous Si

Abstract: Calculated DOS of a-Si:H close to the band gap for different H concentrations in the case of (a) thermodynamic and (b) kinetic H addition.

Cited by 24 publications

References 77 publications

From Femtoseconds to Gigaseconds: The SolDeg Platform for the Performance Degradation Analysis of Silicon Heterojunction Solar Cells

From Femtoseconds to Gigaseconds: The SolDeg Platform for the Performance Degradation Analysis of Silicon Heterojunction Solar Cells

5‐2: Enhanced Bending Endurance with Transverse Tensile Strain and 4‐Terminal Double Gate LTPS TFTs for flexible AMOLED

Effects of Hydrogen Concentration and Cooling Speed on Fabrication of Hydrogenated Amorphous Silicon: Quantum Simulation

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