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P. Roca i Cabarrocas

Bio: P. Roca i Cabarrocas is an academic researcher from École Polytechnique. The author has contributed to research in topics: Silicon & Amorphous silicon. The author has an hindex of 43, co-authored 374 publications receiving 7211 citations. Previous affiliations of P. Roca i Cabarrocas include Princeton University & Centre national de la recherche scientifique.


Papers
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Journal ArticleDOI
TL;DR: In this paper, a radio frequency glow discharge system for the deposition of amorphous thin-film semiconductors and insulators is presented, which is a multiplasma monochamber system consisting of three separated plasma chambers located inside the same isothermal vacuum vessel.
Abstract: We present a study on the development and the evaluation of a fully automated radio‐frequency glow discharge system devoted to the deposition of amorphous thin film semiconductors and insulators. The following aspects were carefully addressed in the design of the reactor: (1) cross contamination by dopants and unstable gases, (2) capability of a fully automated operation, (3) precise control of the discharge parameters, particularly the substrate temperature, and (4) high chemical purity. The new reactor, named ARCAM, is a multiplasma‐monochamber system consisting of three separated plasma chambers located inside the same isothermal vacuum vessel. Thus, the system benefits from the advantages of multichamber systems but keeps the simplicity and low cost of monochamber systems. The evaluation of the reactor performances showed that the oven‐like structure combined with a differential dynamic pumping provides a high chemical purity in the deposition chamber. Moreover, the studies of the effects associated with the plasma recycling of material from the walls and of the thermal decomposition of diborane showed that the multiplasma‐monochamber design is efficient for the production of abrupt interfaces in hydrogenated amorphous silicon (a‐Si:H) based devices. Also, special attention was paid to the optimization of plasma conditions for the deposition of low density of states a‐Si:H. Hence, we also present the results concerning the effects of the geometry, the substrate temperature, the radio frequency power and the silane pressure on the properties of the a‐Si:H films. In particular, we found that a low density of states a‐Si:H can be deposited at a wide range of substrate temperatures (100 °C≤Ts≤300 °C).

226 citations

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TL;DR: In this article, the tetrahedron model was used to determine the hydrogen content, the crystalline fraction, and the void fraction of amorphous and polymorphous silicon films from UV-visible spectroscopic ellipsometry measurements.
Abstract: The dielectric functions of amorphous and polymorphous silicon films prepared under various plasma conditions have been deduced from UV-visible spectroscopic ellipsometry measurements. The measured spectra have been firstsimulated by the use of the Tauc-Lorentz dispersion model and then the compositions of the films have been obtained by the use of the tetrahedron model combined with the Bruggeman effective medium approximation. This approach allows us to determine the hydrogen content, the crystalline fraction, and the void fraction of the films. This is particularly important in the case of polymorphous films in which the low crystalline fraction (below 10%) can only be detected when an accurate description of the effects of hydrogen on the dielectric function through the tetrahedron model is considered. The hydrogen content and film porosity deduced from the analysis of the spectroscopic ellipsometry measurements are in excellent agreement with the hydrogen content and film density deduced from combined elastic recoil detection analysis and Rutherford backscattering spectroscopy measurements. Moreover, despite their high hydrogen content (∼15%-20%) with respect to hydrogenated amorphous silicon films deposited at the same temperature (8%), polymorphous silicon films have a high density, which is related to their very low void fraction.

181 citations

Journal ArticleDOI
TL;DR: In this article, the growth of microcrystalline silicon films produced by the layer-by-layer and standard hydrogen dilution techniques is studied, and it is shown that subsurface reactions play a key role, particularly during the incubation phase where hydrogen is responsible for the formation of a porous layer in which nucleation takes place.
Abstract: The plasma processes and growth reactions involved in the deposition of amorphous, polymorphous and microcrystalline silicon thin films are reviewed. The reference being a-Si:H deposition through surface reactions of SiH 3 radicals, we study the growth of microcrystalline silicon films produced by the layer-by-layer and standard hydrogen dilution techniques. We show that subsurface reactions play a key role, particularly during the incubation phase where hydrogen is responsible for the formation of a porous layer in which nucleation takes place. The evolution of the film properties is related to the long range effects of hydrogen. Coming back to a-Si:H deposition, we further consider the deposition at low substrate temperature (<200°C) and pressure (<5 Pa) where the role of ions is dominant and at deposition rates where powder formation takes place. We propose that rather than a drawback, nanoparticle formation in silane plasmas might be considered as a potential for obtaining new silicon films. We address in particular the deposition of polymorphous silicon consisting of an a-Si:H matrix with silicon nanocrystallites produced in the gas phase. Despite their heterogeneity polymorphous silicon films have improved transport properties and stability with respect to a-Si:H.

180 citations

Journal ArticleDOI
TL;DR: In this paper, the results of an in situ spectroscopic ellipsometry study concerning the substrate dependence of the evolution of microcrystalline silicon films deposited by alternating amorphous silicon deposition and hydrogen plasma treatment were reported.
Abstract: We report the results of an in situ spectroscopic ellipsometry study concerning the substrate dependence of the evolution of microcrystalline silicon films deposited by alternating amorphous silicon deposition and hydrogen plasma treatment. The evolution of the composition of the films during growth, up to thicknesses of ∼100 nm, indicates that besides etching, the diffusion of atomic hydrogen efficiently promotes the growth (and/or nucleation) of buried crystallites. Moreover, the evolution of the films strongly depends on the nature of the substrate. This substrate selectivity is discussed in terms of initial growth processes. The effect of the hydrogen plasma well below the film surface, which produces the thickness‐dependent film composition, along with the substrate selectivity, may be of prime importance in technological applications of microcrystalline silicon.

146 citations

Journal ArticleDOI
TL;DR: The results show that it is possible to increase the volume fraction of the crystalline phase by reducing the deposition time within one cycle or by increasing the hydrogen plasma treatment time.
Abstract: The growth of amorphous and microcrystalline silicon (\ensuremath{\mu}c-Si) films prepared by alternating the deposition of hydrogenated amorphous silicon (a-Si:H) and hydrogen plasma exposure is studied by in situ spectroscopic ellipsometry. The deposition and etching sequences are clearly identified in the real-time ellipsometric trajectories. Insights into the growth of amorphous and microcrystalline silicon materials are obtained from a detailed study of the effects of varying the deposition and hydrogen plasma treatment times as well as the thickness dependence of the film composition. Indeed, we have found that the composition of amorphous and microcrystalline films slowly changes with the increasing film thickness. However, while a-Si:H films becomes porous and rough with the increasing number of cycles, \ensuremath{\mu}c-Si films become denser and their crystalline volume fraction increases. During growth, the transition from a-Si:H to \ensuremath{\mu}c-Si deposition occurs through an intermediate highly porous a-Si:H phase. We suggest that this porous phase is a key element in \ensuremath{\mu}c-Si nucleation, while both selective etching and chemical annealing have to be considered in the growth of the crystallites. Our results show that it is possible to increase the volume fraction of the crystalline phase by reducing the deposition time within one cycle or by increasing the hydrogen plasma treatment time.

129 citations


Cited by
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Journal ArticleDOI
01 Apr 1988-Nature
TL;DR: In this paper, a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) is presented.
Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

9,929 citations

Journal ArticleDOI
TL;DR: The theoretical concepts, experimental tools, and applications of surface photovoltage (SPV) techniques are reviewed in detail in detail as discussed by the authors, where the theoretical discussion is divided into two sections: electrical properties of semiconductor surfaces and the second discusses SPV phenomena.

1,499 citations

Journal ArticleDOI
TL;DR: An overview of gas discharge plasmas can be found in this paper, where the most important applications of these and related plasmmas are discussed, as well as their working principles.

928 citations

Journal ArticleDOI
TL;DR: In this article, the authors describe the use of hydrogenated amorphous silicon (a-Si:H) and hydrogenated micro-crystalline silicon (μc-Si-H) thin films (layers), both deposited at low temperatures (200°C) by plasma-assisted chemical vapour deposition (PECVD), from a mixture of silane and hydrogen.
Abstract: This paper describes the use, within p–i–n- and n–i–p-type solar cells, of hydrogenated amorphous silicon (a-Si:H) and hydrogenated microcrystalline silicon (μc-Si:H) thin films (layers), both deposited at low temperatures (200°C) by plasma-assisted chemical vapour deposition (PECVD), from a mixture of silane and hydrogen. Optical and electrical properties of the i-layers are described. These properties are linked to the microstructure and hence to the i-layer deposition rate, that in turn, affects throughput in production. The importance of contact and reflection layers in achieving low electrical and optical losses is explained, particularly for the superstrate case. Especially the required properties for the transparent conductive oxide (TCO) need to be well balanced in order to provide, at the same time, for high electrical conductivity (preferably by high electron mobility), low optical absorption and surface texture (for low optical losses and pronounced light trapping). Single-junction amorphous and microcrystalline p–i–n-type solar cells, as fabricated so far, are compared in their key parameters (Jsc, FF, Voc) with the [theoretical] limiting values. Tandem and multijunction cells are introduced; the μc-Si: H/a-Si: H or [micromorph] tandem solar cell concept is explained in detail, and recent results obtained here are listed and commented. Factors governing the mass-production of thin-film silicon modules are determined both by inherent technical reasons, described in detail, and by economic considerations. The cumulative effect of these factors results in distinct efficiency reductions from values of record laboratory cells to statistical averages of production modules. Finally, applications of thin-film silicon PV modules, especially in building-integrated PV (BIPV) are shown. In this context, the energy yields of thin-film silicon modules emerge as a valuable gauge for module performance, and compare very favourably with those of other PV technologies. Copyright © 2004 John Wiley & Sons, Ltd.

718 citations

Journal ArticleDOI
TL;DR: In this article, the benefits and challenges of using plasma-based systems in nanofabrication of nanostructured silicon films, low-dimensional semiconducting quantum structures, ordered carbon nanotip arrays, highly crystalline ${\mathrm{TiO}}_{2}$ coatings, and nano-structured hydroxyapatite bioceramics are discussed.
Abstract: The underlying physics of the application of low-temperature, low-pressure reactive plasmas in various nanoassembly processes is described. From the viewpoint of the ``cause and effect'' approach, this Colloquium focuses on the benefits and challenges of using plasma-based systems in nanofabrication of nanostructured silicon films, low-dimensional semiconducting quantum structures, ordered carbon nanotip arrays, highly crystalline ${\mathrm{TiO}}_{2}$ coatings, and nanostructured hydroxyapatite bioceramics. Other examples and future prospects of plasma-aided nanofabrication are also discussed.

675 citations