Thermodynamics and kinetics of hydrogen evolution in hydrogenated amorphous silicon films

Sridhar, N.; Chung, D.D.L.; Anderson, Wayne A.; Coleman, J.

doi:10.1007/bf02655463

Cited by 11 publications

(10 citation statements)

References 28 publications

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“…First, an annealing study investigating possible changes in short range order (Raman HWHM) with H evolution, and whether these changes influence the crystallization kinetics, has previously been reported for films exhibiting a wide range of t o s. [4] While the Raman HWHM's were observed to broaden a little with film annealing (and C H evolution), a trend similar to that observed by Lee et al [10] and by Sridhar et al, [11] the trends observed in Mahan et al [4] were not consistent with the idea that the evolution of more H from a high C H film results in an increase in short range disorder (broader Raman HWHM) during annealing, [9,10] thus increasing the film t o . While, a very weak correlation was observed between the amount of film C H evolved and Raman HWHM broadening for the HWCVD films, [4] there was no correlation between this broadening and the film t o s. In particular, the (10 at.% C H PECVD) film exhibiting the longest incubation time did not exhibit the most Raman broadening after C H evolution, but lay midway between the other two (2.5 and 11.5 at.% C H ) HWCVD films examined, both of which exhibited much shorter t o s.…”

Section: Resultssupporting

confidence: 54%

“…While some differences in final grain size have been reported, and have been attributed largely to variations in r n , the most striking observation for a-Si:H films thermally annealed at 600 8C is the wide range in t o , with values extending from less than 1 h to as long as 10-15 h. These variations in t o and final grain sizes have been interpreted as being due to a wide variety of factors, including differences in film hydrogen content (C H ), [2][3][4] deposition type, [3,4] film stress, [5] source gases, [6] defect formation, [7] structural disorder, either in as grown films [8,9] or as a result of H effusion during annealing, [10,11] and, for films grown at high temperatures, the (unintentional) incorporation of crystallite seeds. [1,12] Largely missing from these studies has been any information or conjectures as to what constitutes a nucleation center in a-Si:H, and how the nature of these centers may determine or influence t o .…”

Section: Introductionmentioning

confidence: 99%

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Identification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous Silicon

Mahan

Williamson

et al. 2009

Adv Funct Materials

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Utilizing the concepts of a critical crystallite size and local film inhomogeneity, it is shown that nucleation in thermally annealed hydrogenated amorphous silicon occurs in the more well ordered spatial regions in the network, which are defined by the initial inhomogeneous H distributions in the as‐grown films. Although the film H evolves very early during annealing, the local film order is largely retained in the still amorphous films even after the vast majority of the H is evolved, and the more well ordered regions which are the nucleation center sites for crystallization are those spatial regions which do not initially contain clustered H, as probed by H NMR spectroscopy. The sizes of these better ordered regions relative to a critical crystallite size determine the film incubation times (the time before the onset of crystallization). Changes in film short range order upon H evolution, and the presence of microvoid type structures in the as grown films play no role in the crystallization process. While the creation of dangling bonds upon H evolution may play a role in the actual phase transformation itself, the film defect densities measured just prior to the onset of crystallization exhibit no trends which can be correlated with the film incubation times.

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Section: Resultssupporting

confidence: 54%

Section: Introductionmentioning

confidence: 99%

Identification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous Silicon

Mahan

Williamson

et al. 2009

Adv Funct Materials

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“…6 Studies in the literature suggest that HT evolution is rate limited by diffusion of atomic hydrogen in a-Si, while LT evolution is limited by surface desorption of molecular hydrogen from void rich a-Si. 5,[23][24][25][26] The desorption energy can be determined by applying the following surface desorption rate equation to the low temperature peaks:…”

Section: B Tritium Effusionmentioning

confidence: 99%

Hydrogen effusion from tritiated amorphous silicon

Kherani

Liu

Virk

et al. 2008

Journal of Applied Physics

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Results for the effusion and outgassing of tritium from tritiated hydrogenated amorphous silicon (a-Si:H:T) films are presented. The samples were grown by dc-saddle field glow discharge at various substrate temperatures between 150 and 300°C. The tracer property of radioactive tritium is used to detect tritium release. Tritium effusion measurements are performed in a nonvacuum ion chamber and are found to yield similar results as reported for standard high vacuum technique. The results suggest for decreasing substrate temperature the growth of material with an increasing concentration of voids. These data are corroborated by analysis of infrared absorption data in terms of microstructure parameters. For material of low substrate temperature (and high void concentration) tritium outgassing in air at room temperature was studied, and it was found that after 600h about 0.2% of the total hydrogen (hydrogen+tritium) content is released. Two rate limiting processes are identified. The first process, fast tritium outgassing with a time constant of 15h, seems to be related to surface desorption of tritiated water (HTO) with a free energy of desorption of 1.04eV. The second process, slow tritium outgassing with a time constant of 200–300h, appears to be limited by oxygen diffusivity in a growing oxide layer. This material of lowest H stability would lose half of the hydrogen after 60years.

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“…This observation is supported by the fact that hydrogen associated with nano-sized voids starts to diffuse out at 150-400 C, whereas hydrogen present in divacancies escapes around 550-600 C. 36 It can be, therefore, concluded that the films with a larger concentration of nano-voids, i.e., higher values of R*, undergo larger structural changes upon annealing. [36][37][38][39][40] To further investigate the impact of the hydrogen outdiffusion in high R* films, ex situ XRD measurements were also carried out on the samples after annealing at 450 C and 550 C. Figure 7 shows the change in x 2h during annealing as a function of R* for different C H values. The MRO is found to increase upon annealing for the films characterized by a higher R*.…”

Section: -3mentioning

confidence: 99%

In situ crystallization kinetics studies of plasma-deposited, hydrogenated amorphous silicon layers

Sharma

Verheijen

Sanden

et al. 2012

Journal of Applied Physics

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Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers) Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. The impact of the amorphous silicon properties, i.e., the microstructure parameter R* and the medium range order (MRO), on the crystallization process is highlighted and discussed. In agreement with literature, the development of large grains extending through the thickness of the poly-Si layer is found to be promoted by an increase in the amorphous silicon microstructure parameter, R*. Furthermore, while the role of the MRO in controlling the incubation time and, therefore, the onset in crystallization is generally acknowledged, it is also concluded that the presence of nano-sized voids plays an essential role in the crystallization kinetics.

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Thermodynamics and kinetics of hydrogen evolution in hydrogenated amorphous silicon films

Cited by 11 publications

References 28 publications

Identification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous Silicon

Identification of Nucleation Center Sites in Thermally Annealed Hydrogenated Amorphous Silicon

Hydrogen effusion from tritiated amorphous silicon

In situ crystallization kinetics studies of plasma-deposited, hydrogenated amorphous silicon layers

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