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Brent P. Nelson

Bio: Brent P. Nelson is an academic researcher from National Renewable Energy Laboratory. The author has contributed to research in topics: Chemical vapor deposition & Amorphous silicon. The author has an hindex of 18, co-authored 73 publications receiving 1981 citations.


Papers
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Journal ArticleDOI
TL;DR: The absorption strength of the stretching modes does not depend on the details of sample preparation, contrary to hypotheses previously invoked to explain experimental data, and previously published data for both the wagging and stretching modes are consistent with the proportionality factors determined.
Abstract: We have used infrared transmission and nuclear-reaction analysis to determine the ir absorption strength of the Si-H wagging and stretching modes in hydrogenated amorphous silicon (a-Si:H). The films were deposited by plasma-assisted chemical vapor deposition and reactive magnetron sputtering. We show that the widely used ir-data-analysis method of Brodsky, Cardona, and Cuomo can lead to significant errors in determining the absorption coefficients, particularly for films less than \ensuremath{\sim}1 \ensuremath{\mu}m thick. To eliminate these errors we explicitly take into account the effects of optical interference to analyze our data. We show that the hydrogen content can be determined from the stretching modes at \ensuremath{\omega}=2000 and 2100 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ as well as the wagging mode at \ensuremath{\omega}=640 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$. By assigning different oscillator strengths to the 2000- and 2100-${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ modes, we show that the absorption strength of the stretching modes does not depend on the details of sample preparation, contrary to hypotheses previously invoked to explain experimental data. We obtain ${\mathit{A}}_{640}$=(2.1\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$, ${\mathit{A}}_{2000}$=(9.0\ifmmode\pm\else\textpm\fi{}1.0)\ifmmode\times\else\texttimes\fi{}${10}^{19}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$, and ${\mathit{A}}_{2100}$=(2.2\ifmmode\pm\else\textpm\fi{}0.2)\ifmmode\times\else\texttimes\fi{}${10}^{20}$ ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}2}$ for the proportionality constants between the hydrogen concentration and the integrated absorbance of the wagging and stretching modes. The value of ${\mathit{A}}_{640}$ is \ensuremath{\sim}30% larger than the generally used value. We show that previously published data for both the wagging and stretching modes are consistent with the proportionality factors determined in the present study.

564 citations

Journal ArticleDOI
TL;DR: In this paper, it was shown that hydrogenated amorphous silicon containing as little as 1/10 the bonded H observed in device-quality glow discharge films have been deposited by thermal decomposition of silane on a heated filament.
Abstract: Device‐quality hydrogenated amorphous silicon containing as little as 1/10 the bonded H observed in device‐quality glow discharge films have been deposited by thermal decomposition of silane on a heated filament. These low H content films show an Urbach edge width of 50 mV and a spin density of ∼1/100 as large as that of glow discharge films containing comparable amounts of H. High substrate temperatures, deposition in a high flux of atomic H, and lack of energetic particle bombardment are suggested as reasons for this behavior.

464 citations

Journal ArticleDOI
TL;DR: In this article, a transition from amorphous (a-) to microcrystalline (μc-) silicon was prepared by hot-wire chemical vapor deposition using silane decomposition with either varied hydrogen-to-silane ratio, R, or with fixed R=3 but a varied substrate temperature, Ts. Raman results indicate that there is a threshold for the structural transition from a- to μc-Si:H in both cases.
Abstract: Transition films from amorphous (a-) to microcrystalline (μc-) silicon were prepared by hot-wire chemical vapor deposition using silane decomposition with either varied hydrogen-to-silane ratio, R, or with fixed R=3 but a varied substrate temperature, Ts. Raman results indicate that there is a threshold for the structural transition from a- to μc-Si:H in both cases. The onset of the structural transition is found to be R≈2 at Ts=250 °C and Ts≈200 °C at R=3. The properties of the material were studied by infrared absorption, optical absorption, photoluminescence (PL), and conductivity temperature dependence. We observed that the peak frequency of the SiH wag mode remains at 630−640 cm−1 for all the films, but the hydrogen content shows two regimes of fast and slow decreases separated by the onset of microcrystallinity. When microcrystallinity increased, we observed that (a) the SiO vibration absorption at 750 cm−1 and 1050−1200 cm−1 appeared, (b) the relative intensity of the 2090 cm−1 absorption increased...

101 citations

Journal ArticleDOI
TL;DR: The microstructure of hydrogenated amorphous silicon carbon alloys has been analyzed by smallangle x-ray scattering, infrared absorption, and density measurements as discussed by the authors, and the microvoid number density increases from about 5×1019/cm3 for a •Si:H to about 4×1020/ cm3 for •Si 0.7 C 0.3 :H.
Abstract: The microstructure of hydrogenated amorphous silicon‐carbon alloys has been analyzed by small‐angle x‐ray scattering, infrared absorption, and density measurements. Decreasing density with C incorporation is due to microvoids about 0.6 nm in average radius, which are either approximately spherical in shape or randomly oriented nonspheres. The microvoid number density increases from about 5×1019/cm3 for a‐Si:H to about 4×1020/cm3 for a‐Si0.7 C0.3 :H. The CH3 species probably causes the enhanced microvoid formation in these alloys. A large fraction of the microvoid surfaces is not hydrogenated.

97 citations

Journal ArticleDOI
TL;DR: In this paper, the authors examined the structure of a-Si:H, deposited at rates in excess of 100 A/s by the hot wire chemical vapor deposition technique, has been examined by X-ray diffraction (XRD), Raman spectroscopy, H evolution, and small-angle x-ray scattering (SAXS).
Abstract: The structure of a-Si:H, deposited at rates in excess of 100 A/s by the hot wire chemical vapor deposition technique, has been examined by x-ray diffraction (XRD), Raman spectroscopy, H evolution, and small-angle x-ray scattering (SAXS). The films examined in this study were chosen to have roughly the same bonded H content CH as probed by infrared spectroscopy. As the film deposition rate Rd is increased from 5 to >140 A/s, we find that the short range order (from Raman), the medium range order (from XRD), and the peak position of the H evolution peak are invariant with respect to deposition rate, and exhibit structure consistent with a state-of-the-art, compact a-Si:H material deposited at low deposition rates. The only exception to this behavior is the SAXS signal, which increases by a factor of ∼100 over that for our best, low H content films deposited at ∼5 A/s. We discuss the invariance of the short and medium range order in terms of growth models available in the literature, and relate changes in th...

78 citations


Cited by
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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 paper, the photo-induced properties of amorphous semiconductors, including chalcogenide glasses, are reviewed and the features exhibited in common by all types of these materials, whether in the experimentally observed photoinduced metastability or the theoretical models used to account for such behaviour are stressed.
Abstract: Amorphous semiconductors, being intrinsically metastable in nature, exhibit a wide variety of changes in their physical properties, particularly when photoinduced using bandgap illumination. This article reviews the photoinduced phenomena exhibited by amorphous semiconductors such as amorphous hydrogenated silicon (and other tetrahedrally coordinated materials) and chalcogenide glasses. Features exhibited in common by all types of amorphous semiconductors, whether in the experimentally observed photoinduced metastability or the theoretical models used to account for such behaviour, are stressed.

524 citations

Patent
29 Sep 2000
TL;DR: In this paper, the authors propose a device integration method and integrated device, which involves the steps of directly bonding a semiconductor device having a substrate to an element; and removing a portion of the substrate to expose a remaining part of the semiconductor devices after bonding.
Abstract: A device integration method and integrated device. The method may include the steps of directly bonding a semiconductor device having a substrate to an element; and removing a portion of the substrate to expose a remaining portion of the semiconductor device after bonding. The element may include one of a substrate used for thermal spreading, impedance matching or for RF isolation, an antenna, and a matching network comprised of passive elements. A second thermal spreading substrate may be bonded to the remaining portion of the semiconductor device. Interconnections may be made through the first or second substrates. The method may also include bonding a plurality of semiconductor devices to an element, and the element may have recesses in which the semiconductor devices are disposed. A conductor array having a plurality of contact structures may be formed on an exposed surface of the semiconductor device, vias may be formed through the semiconductor device to device regions, and interconnection may be formed between said device regions and said contact structures.

354 citations

Journal ArticleDOI
TL;DR: The status of current and coming solar photovoltaic technologies and their future development are presented in this paper, where the emphasis is on R&D advances and cell and module performances, with indications of the limitations and strengths of crystalline (Si and GaAs) and thin film (a-Si:H, Si, Cu(In,Ga)(Se,S)2, CdTe).

300 citations