Control of silicon network structure in plasma deposition

Tsai, C. C.; Anderson, G. B.; Thompson, R.; Wacker, B.

doi:10.1016/0022-3093(89)90096-3

Cited by 250 publications

(106 citation statements)

References 6 publications

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“…The various models proposed for the description of c-Si:H growth, such as the partial chemical equilibrium 29 or therewith related to the selective-etching model, 30 the surface diffusion model, 1 and the chemical annealing model, 31,32 have in common that a high hydrogen radical density is considered to be critical for the formation of c-Si:H. A recent study in the VHF-hphP regime shows a good agreement with the above results. 33 To fulfil such conditions, c-Si:H is mostly prepared with a high dilution of the silicon precursor gas, usually silane, with hydrogen together with an effective dissociation of these gases by a high discharge power in PECVD or high filament temperatures in hot-wire chemical vapor deposition ͑HWCVD͒.…”

Section: A Structure Adjustment For Opm C-si:h Materialssupporting

confidence: 71%

Microcrystalline silicon solar cells deposited at high rates

Mai

Klein

Carius

et al. 2005

Journal of Applied Physics

183

123

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Hydrogenated microcrystalline silicon ͑ c-Si:H͒ thin-film solar cells were prepared at high rates by very high frequency plasma-enhanced chemical vapor deposition under high working pressure. The influence of deposition parameters on the deposition rate ͑R D ͒ and the solar cell performance were comprehensively studied in this paper, as well as the structural, optical, and electrical properties of the resulting solar cells. Reactor-geometry adjustment was done to achieve a stable and homogeneous discharge under high pressure. Optimum solar cells are always found close to the transition from microcrystalline to amorphous growth, with a crystallinity of about 60%. At constant silane concentration, an increase in the discharge power did hardly increase the deposition rate, but did increase the crystallinity of the solar cells. This results in a shift of the c-Si:H/a-Si:H transition to higher silane concentration, and therefore leads to a higher R D for the optimum cells. On the other hand, an increase in the total flow rate at constant silane concentration did lead to a higher R D , but lower crystallinity. With this shift of the c-Si:H/a-Si:H transition at higher flow rates, the R D for the optimum cells decreased. A remarkable structure development along the growth axis was found in the solar cells deposited at high rates by a "depth profile" method, but this does not cause a deterioration of the solar cell performance apart from a poorer blue-light response. As a result, a c-Si:H single-junction p-i-n solar cell with a high efficiency of 9.8% was deposited at a R D of 1.1 nm/s.

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Section: A Structure Adjustment For Opm C-si:h Materialssupporting

confidence: 71%

Microcrystalline silicon solar cells deposited at high rates

Mai

Klein

Carius

et al. 2005

Journal of Applied Physics

183

123

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“…[17]. Interestingly our results gives some indication on the local growth mechanisms, as the a-Si to mc-Si transition is usually attributed either to an enhancement of the surface diffusion of the SiH x precursors [33] or to a selective etching of the weakly bonded Si atoms [34][35][36][37]. In our case, the increase of the hydrogen content at constant temperature leads to an increase of crystallinity because the selective etching mechanism start to dominate (whereas the surface diffusion remains moderate), while, for constant radical flows, the increase of temperature leads to a strong enhancement of the surface diffusion, leading both to an increase in crystallinity and to a filling of the cracks.…”

Section: Discussionmentioning

confidence: 57%

Microcrystalline silicon solar cells: effect of substrate temperature on cracks and their role in post‐oxidation

Python

Dominé

Söderström

et al. 2010

Progress in Photovoltaics

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Microcrystalline silicon (mc-Si:H) cells can reach efficiencies up to typically 10% and are usually incorporated in tandem micromorph devices. When cells are grown on rough substrates, ''cracks'' can appear in the mc-Si:H layers. Previous works have demonstrated that these cracks have mainly detrimental effects on the fill factor and open-circuit voltage, and act as bad diodes with a high reverse saturation current. In this paper, we clarify the nature of the cracks, their role in postoxidation processes, and indicate how their density can be reduced. Regular secondary ion mass spectrometry (SIMS) and local nano-SIMS measurements show that these cracks are prone to local post-oxidation and lead to apparent high oxygen content in the layer. Usually the number of cracks can be decreased with an appropriate modification of the substrate surface morphology, but then, the required light scattering effect is reduced due to a lower roughness. This study presents an alternative/complementary way to decrease the crack density by increasing the substrate temperature during deposition. These results, also obtained when performing numerical simulation of the growth process, are attributed to the enhanced surface diffusion of the adatoms at higher deposition temperature. We evaluate the cracks density by introducing a fast method to count cracks with good statistics over approximately 4000 mm of sample cross-section. This method is proven to be useful to quickly visualize the impact of substrate morphology on the density of cracks in microcrystalline and in micromorph devices, which is an important issue in the manufacturing process of modules.

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“…The possibility of reaching high growth rates at moderate temperatures has made PECVD particularly appealing for generating amorphous (a), microcrystalline ( c), and nanocrystalline (nc) films, of particular importance, e.g., in the production of solar cells [1]. By reducing the growth rate [2] or by raising the substrate temperature [3] also epitaxial silicon films of good quality can be obtained. This versatility surely makes PECVD of extreme scientific interest.…”

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confidence: 99%

Thermal-Hydrogen Promoted Selective Desorption and Enhanced Mobility of Adsorbed Radicals in Silicon Film Growth

et al. 2008

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Car-Parrinello simulations and static density-functional theory calculations reveal how hydrogen promotes growth of epitaxial, ordered Si films in plasma-enhanced chemical vapor deposition at lowtemperature conditions where the exposed Si 001 -2 1 surface is fully hydrogenated. Thermal H atoms, indeed, are shown to selectively etch adsorbed silyl back to the gas phase or to form adsorbed species which can be easily incorporated into the crystal down to T 200 C and start diffusing around T 300 C. Our results are well consistent with earlier experiments. DOI: 10.1103/PhysRevLett.100.046105 PACS numbers: 81.15.Gh, 68.43.Bc, 68.47.Fg Plasma-enhanced chemical vapor deposition (PECVD) is a very popular technique for growing silicon films. The possibility of reaching high growth rates at moderate temperatures has made PECVD particularly appealing for generating amorphous (a), microcrystalline ( c), and nanocrystalline (nc) films, of particular importance, e.g., in the production of solar cells [1]. By reducing the growth rate [2] or by raising the substrate temperature [3] also epitaxial silicon films of good quality can be obtained. This versatility surely makes PECVD of extreme scientific interest. Among the large amount of information coming out of decades of experiments and production, one phenomenon has captured particular attention, leading to several, sometimes controversial, interpretations. Increasing amounts of hydrogen impinging the surface were indeed shown to enhance crystallinity both during growth, and/or in post-growth treatments [2,4,5]. The observation of a simultaneous decrease in the growth rate, and/or of the thinning of the samples during hydrogen exposure, strongly suggested hydrogen to be able to preferentially etch noncrystalline regions [2,6]. A further, possibly complementary channel for H-induced crystallinity in postgrowth exposure was also proposed [5]. While very many indications for possible competing mechanisms were given based on experimental observations, the complexity of the problem, in terms of geometry, chemistry, and the multitude of species involved, has prevented so far the development of a parameter-free quantitative modeling of the process at the atomic scale able to shed full light on the phenomenon.In this Letter we shall focus on the role played by hydrogen during silicon-film growth starting from a fully hydrogenated Si 001 -2 1 representative of the initial stages of low-temperature deposition, where thermal H desorption is not activated [7]. Our study has been motivated by the wide interest in hydrogen-induced crystallization, and, more specifically, by the seminal paper of Tsai et al. [2] in which it is demonstrated the possibility of growing epitaxial Si films with PECVD at a very low temperature T 200 C, provided that silane is introduced in the reactor strongly diluted with H 2 . In their paper, Tsai et al. suggested preferential etching of nonepitaxial adsorbed species to cause the improved quality of the grown sample. Hydrogen etching is proposed to be selecti...

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Control of silicon network structure in plasma deposition

Cited by 250 publications

References 6 publications

Microcrystalline silicon solar cells deposited at high rates

Microcrystalline silicon solar cells deposited at high rates

Microcrystalline silicon solar cells: effect of substrate temperature on cracks and their role in post‐oxidation

Thermal-Hydrogen Promoted Selective Desorption and Enhanced Mobility of Adsorbed Radicals in Silicon Film Growth

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