Mechanism of hydrogen-induced crystallization of amorphous silicon
TL;DR: The mechanism of hydrogen-induced crystallization of hydrogenated amorphous silicon films during post-deposition treatment with an H2 (or D2) plasma is reported, which is mediated by the insertion of H atoms into strained Si–Si bonds as the atoms diffuse through the film.
Abstract: Hydrogenated amorphous and nanocrystalline silicon films manufactured by plasma deposition techniques are used widely in electronic and optoelectronic devices1,2. The crystalline fraction and grain size of these films determines electronic and optical properties; the nanocrystal nucleation mechanism, which dictates the final film structure, is governed by the interactions between the hydrogen atoms of the plasma and the solid silicon matrix. Fundamental understanding of these interactions is important for optimizing the film structure and properties. Here we report the mechanism of hydrogen-induced crystallization of hydrogenated amorphous silicon films during post-deposition treatment with an H2 (or D2) plasma. Using molecular-dynamics simulations3,4 and infrared spectroscopy5, we show that crystallization is mediated by the insertion of H atoms into strained Si–Si bonds as the atoms diffuse through the film. This chemically driven mechanism may be operative in other covalently bonded materials, where the presence of hydrogen leads to disorder-to-order transitions.
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TL;DR: The unique plasma-specific features and physical phenomena in the organization of nanoscale soild-state systems in a broad range of elemental composition, structure, and dimensionality are critically reviewed in this paper.
Abstract: The unique plasma-specific features and physical phenomena in the organization of nanoscale soild-state systems in a broad range of elemental composition, structure, and dimensionality are critically reviewed. These effects lead to the possibility to localize and control energy and matter at nanoscales and to produce self-organized nano-solids with highly unusual and superior properties. A unifying conceptual framework based on the control of production, transport, and self-organization of precursor species is introduced and a variety of plasma-specific non-equilibrium and kinetics-driven phenomena across the many temporal and spatial scales is explained. When the plasma is localized to micrometer and nanometer dimensions, new emergent phenomena arise. The examples range from semiconducting quantum dots and nanowires, chirality control of single-walled carbon nanotubes, ultra-fine manipulation of graphenes, nano-diamond, and organic matter to nano-plasma effects and nano-plasmas of different states of matter.
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TL;DR: Plasma-aided nanofabrication is a rapidly expanding area of research spanning disciplines ranging from physics and chemistry of plasmas and gas discharges to solid state physics, materials science, surface science, nanoscience and nanotechnology and related engineering subjects as discussed by the authors.
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282 citations
TL;DR: In this article, the important fundamental mechanisms of nanocrystal formation in plasmas, reviews the range of synthesis approaches reported in the literature and discusses some of the potential applications of plasma-synthesized semiconductor nanocrystals.
Abstract: Semiconductor nanocrystals have attracted considerable interest for a wide range of applications including light-emitting devices and displays, photovoltaic cells, nanoelectronic circuit elements, thermoelectric energy generation and luminescent markers in biomedicine A particular advantage of semiconductor nanocrystals compared with bulk materials rests in their size-tunable optical, mechanical and thermal properties While nanocrystals of ionically bonded semiconductors can conveniently be synthesized with liquid phase chemistry, covalently bonded semiconductors require higher synthesis temperatures Over the past decade, nonthermal plasmas have emerged as capable synthetic approaches for the covalently bonded semiconductor nanocrystals Among the main advantages of nanocrystal synthesis in plasmas is the unipolar electrical charging of nanocrystals that helps avoid or reduce particle agglomeration and the selective heating of nanoparticles immersed in low-pressure plasmas This paper discusses the important fundamental mechanisms of nanocrystal formation in plasmas, reviews the range of synthesis approaches reported in the literature and discusses some of the potential applications of plasma-synthesized semiconductor nanocrystals
259 citations
Cites background from "Mechanism of hydrogen-induced cryst..."
...While other mechanisms may play a role as well in the crystal formation of some materials, such as hydrogen-induced crystallization in the case of silicon [81], we believe that the selective nanoparticle heating plays a central role....
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TL;DR: In this article, H2 plasma treatments are used during film deposition to improve the passivation of the a-Si:H layers, and 4 cm2 heterojunction solar cells were produced with industry compatible processes, yielding open-circuit voltages up to 725 mV and aperture area efficiencies up to 21%.
Abstract: Silicon heterojunction solar cells have high open-circuit voltages thanks to excellent passivation of the wafer surfaces by thin intrinsic amorphous silicon (a-Si:H) layers deposited by plasma-enhanced chemical vapor deposition. We show a dramatic improvement in passivation when H2 plasma treatments are used during film deposition. Although the bulk of the a-Si:H layers is slightly more disordered after H2 treatment, the hydrogenation of the wafer/film interface is nevertheless improved with as-deposited layers. Employing H2 treatments, 4 cm2 heterojunction solar cells were produced with industry-compatible processes, yielding open-circuit voltages up to 725 mV and aperture area efficiencies up to 21%.
252 citations
References
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IBM1
TL;DR: A new potential for silicon is presented, along with results of extensive tests which suggest that this potential provides a rather realistic description of silicon.
Abstract: Empirical interatomic potentials permit the calculation of structural properties and energetics of complex systems. A new approach for constructing such potentials, by explicitly incorporating the dependence of bond order on local environment, permits an improved description of covalent materials. In particular, a new potential for silicon is presented, along with results of extensive tests which suggest that this potential provides a rather realistic description of silicon. The limitations of the potential are discussed in detail.
2,902 citations
"Mechanism of hydrogen-induced cryst..." refers methods in this paper
...The interatomic interactions in the MD simulations were described by an extension of Tersoff's empirical potential for Si, to include Si–H, H–H, and the corresponding three-body interaction...
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TL;DR: The advantages and limitations of photovoltaic solar modules for energy generation are reviewed with their operation principles and physical efficiency limits, and recent developments suggest that thin-film crystalline silicon (especially microcrystalline silicon) is becoming a prime candidate for future photov electricity generation.
Abstract: The advantages and limitations of photovoltaic solar modules for energy generation are reviewed with their operation principles and physical efficiency limits. Although the main materials currently used or investigated and the associated fabrication technologies are individually described, emphasis is on silicon-based solar cells. Wafer-based crystalline silicon solar modules dominate in terms of production, but amorphous silicon solar cells have the potential to undercut costs owing, for example, to the roll-to-roll production possibilities for modules. Recent developments suggest that thin-film crystalline silicon (especially microcrystalline silicon) is becoming a prime candidate for future photovoltaics.
1,177 citations
"Mechanism of hydrogen-induced cryst..." refers methods in this paper
...jpg" NDATA ITEM> ]> Hydrogenated amorphous and nanocrystalline silicon films manufactured by plasma deposition techniques are used widely in electronic and optoelectronic device...
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TL;DR: The theoretical and experimental foundation of surface IR spectroscopy is described and selected examples are presented to illustrate the kind of information derived in several important areas of surface science such as chemistry, structure, dynamics and kinetics at surfaces as discussed by the authors.
760 citations
"Mechanism of hydrogen-induced cryst..." refers methods in this paper
...The Si–D absorption band was deconvoluted using seven gaussian absorption peaks corresponding to the stretching modes of Si–D–Si and of surface and bulk silicon deuterides on the basis of well known peak assignments for Si–D(H) absorptions in c-Si, a-Si:H and a-Si:...
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IBM1
TL;DR: The behavior of hydrogen in crystalline silicon is examined with state-of-the-art theoretical techniques, based on the pseudopotential-density-functional method in a supercell geometry, finding hydrogen-assisted vacancy formation is found to be an exothermic process.
Abstract: The behavior of hydrogen in crystalline silicon is examined with state-of-the-art theoretical techniques, based on the pseudopotential-density-functional method in a supercell geometry. Stable sites, migration paths, and barriers for different charge states are explored and displayed in total-energy surfaces that provide immediate insight into these properties. The bond-center site is the global minimum for the neutral and positive charge states; in the negative charge state, the tetrahedral interstitial site is preferred. The positive charge state is energetically favorable in p-type material, providing a mechanism for passivation of shallow acceptors: electrons from the H atoms annihilate the free holes, and formation of H-acceptor pairs follows compensation. Also addressed are the issues of molecule formation and hydrogen-induced damage. A number of different mechanisms for defect formation are examined; hydrogen-assisted vacancy formation is found to be an exothermic process.
407 citations
"Mechanism of hydrogen-induced cryst..." refers background in this paper
...During diffusion through the film, H inserts into strained Si–Si bonds, forming intermediate bond-centred Si–H–Si configuration...
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PARC1
TL;DR: In this article, the concept of film formation as a balance between deposition and "etching" of the growing surface is discussed, which reduces the temperature required to remove weak or strained bonds and produces device quality a-Si:H.
Abstract: Controllability of the Si network structure ranging from amorphous to microcrystalline, polycrystalline, or epitaxial growth has been achieved in conventional glow discharge of silane by controlling the extent of hydrogen ‘etching’ during film growth. The concept of film formation as a balance between deposition and ‘etching’ of the growing surface is discussed. Since energetically unfavorable configurations are preferentially eliminated, ‘etching’ reduces the temperature required to remove weak or strained bonds and produces device quality a-Si:H. It is also responsible for achieving low temperature crystallinity.
242 citations