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Journal ArticleDOI

Deposition of device quality, low H content amorphous silicon

01 May 1991-Journal of Applied Physics (American Institute of Physics)-Vol. 69, Iss: 9, pp 6728-6730
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.
Citations
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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

Journal ArticleDOI
TL;DR: In this paper, the status, and future directions of the cell and module technologies, with emphasis on the research and development aspects, are discussed, including issues that are considered important for the development of specific materials, cell, and module approaches.
Abstract: This review centers on the status, and future directions of the cell and module technologies, with emphasis on the research and development aspects. The framework is established with a consideration of the historical parameters of photovoltaics and each particular technology approach. The problems and strengths of the single-crystal, polycrystalline, and amorphous technologies are discussed, compared, and assessed. Single- and multiple junction or tandem cell configurations are evaluated for performance, processing, and engineering criteria. Thin-film technologies are highlighted as emerging, low-cost options for terrestrial applications and markets. Discussions focus on the fundamental building block for the photovoltaic system, the solar cell, but important module developments and issues are cited. Future research and technology directions are examined, including issues that are considered important for the development of the specific materials, cell, and module approaches. Novel technologies and new research areas are surveyed as potential photovoltaic options of the future.

175 citations

Journal ArticleDOI
TL;DR: In this paper, the absolute densities of H atoms produced in catalytic chemical vapor deposition (Cat-CVD or hot-wire CVD) processes were determined by employing two-photon laser-induced fluorescence and vacuum ultraviolet absorption techniques.
Abstract: The absolute densities of H atoms produced in catalytic chemical vapor deposition (Cat-CVD or hot-wire CVD) processes were determined by employing two-photon laser-induced fluorescence and vacuum ultraviolet absorption techniques. The H-atom density in the gas phase increases exponentially with increases in the catalyzer temperature in the presence of pure H2. When the catalyzer temperature was 2200 K, the absolute density in the presence of 5.6 Pa of H2 (150 sccm in flow rate) was as high as 1.5×1014 cm−3 at a point 10 cm from the catalyzer. This density is one or two orders of magnitude higher than those observed in typical plasma-enhanced chemical vapor-deposition processes. The H-atom density decreases sharply with the addition of SiH4. When 0.1 Pa of SiH4 was added, the steady-state density decreased to 7×1012 cm−3. This sharp decrease can primarily be ascribed to the loss processes on chamber walls.

144 citations

Journal ArticleDOI
TL;DR: In this paper, the Staebler-Wronski effect is associated with the relatively high diffusion coefficient of hydrogen and the changes in local bonding coordination promoted by hydrogen, and the fundamental aspects of the interplay between hydrogen and electronic energy states that form the basis of competing microscopic models for explaining the degradation effect.
Abstract: ▪ Abstract Hydrogenated amorphous silicon (a-Si:H) exhibits a metastable light-induced degradation of its optoelectronic properties that is called the Staebler-Wronski effect, after its discoverers. This degradation effect is associated with the relatively high diffusion coefficient of hydrogen and the changes in local bonding coordination promoted by hydrogen. Reviewed are the fundamental aspects of the interplay between hydrogen and electronic energy states that form the basis of competing microscopic models for explaining the degradation effect. These models are tested against the latest experimental observations, and material and preparation parameters that reduce the Staebler-Wronski effect are discussed.

136 citations

Journal ArticleDOI
TL;DR: In this article, the authors discuss the progress, outstanding problems, and environmental issues associated with bulk Si, thin-film, and high-efficiency multi-junction solar cells, which form the basis of the so-called third generation photovoltaics technologies.

130 citations

References
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Journal ArticleDOI
TL;DR: In this article, the authors investigated the influence of the Staebler-Wronski effect on undoped hydrogenated amorphous silicon with electron spin resonance and photoconductivity measurements.
Abstract: We study the magnitude of metastable light-induced changes in undoped hydrogenated amorphous silicon (the Staebler-Wronski effect) with electron-spin-resonance and photoconductivity measurements. The influence of the following parameters is investigated in a systematic way: sample thickness, impurity content, illumination time, light intensity, photon energy, and illumination and annealing temperatures. The experimental results can be explained quantitatively by a model based on the nonradiative recombination of photoexcited carriers as the defect-creating step. In the framework of this model, the Staebler-Wronski effect is an intrinsic, self-limiting bulk process, characterized by a strongly sublinear dependence on the total light exposure of a sample. The experimental results suggest that the metastable changes are caused by recombination-induced breaking of weak Si--Si bonds, rather than by trapping of excess carriers in already existing defects. Hydrogen could be involved in the microscopic mechanism as a stabilizing element. The main metastable defect created by prolonged illumination is the silicon dangling bond. An analysis of the annealing behavior shows that a broad distribution of metastable dangling bonds exists, characterized by a variation of the energy barrier separating the metastable state from the stable ground state between 0.9 and 1.3 eV.

990 citations

Journal ArticleDOI
George Dewey Cody1, Thomas Tiedje1, B. Abeles1, B.G. Brooks1, Y. Goldstein1 
TL;DR: The effect of thermal and structural disorder on the electronic structure of hydrogenated amorphous silicon is investigated by measurement of the shape of the optical absorption edge as a function of temperature and thermal evolution of hydrogen as discussed by the authors.
Abstract: The effect of thermal and structural disorder on the electronic structure of hydrogenated amorphous silicon is investigated by measurement of the shape of the optical absorption edge as a function of temperature and thermal evolution of hydrogen. The data are consistent with the idea that the thermal and structural disorder are additive, and suggest that the disorder, rather than the hydrogen content, is the fundamental determining factor in the optical band gap.

974 citations

Journal ArticleDOI
TL;DR: The correlation between dangling-bond defect density and the slope of the Urbach tail in hydrogenated amorphous silicon is examined in this article, and it is shown that this correlation can be explained quantitatively by a spontaneous decay of the weakest bonding orbitals into non-bonding defects during deposition or annealing of a sample and that the same correlation holds for all types of disorder affecting the edge of the urbach edge.
Abstract: The correlation between the density of dangling-bond defects and the slope of the Urbach tail in hydrogenated amorphous silicon is examined. It is shown that this correlation can be explained quantitatively by a spontaneous decay of the weakest bonding orbitals into non-bonding defects during deposition or annealing of a sample and that the same correlation holds for all types of disorder affecting the slope of the Urbach edge. The temperature dependence of the defect density as well as the creation of metastable defects are discussed, and quantitative expressions are derived which can be used to estimate the quality and the stability of a given sample on the basis of the slope of its Urbach tail alone. Possible ways for future improvement of the material are indicated.

295 citations

Journal ArticleDOI
TL;DR: In this paper, a simplified model for the deposition process is suggested based on this data and other information, and a novel substrate holder is used to control the growth of a•Si:H growth on nearby substrates.
Abstract: High‐quality hydrogenated amorphous silicon films (a‐Si:H) have been produced by decomposition of low‐pressure silane gas on a very hot surface with deposition on a nearby, typically 210 °C substrate. A high‐temperature tungsten filament provides the surface for heterogeneous thermal decomposition of the low‐pressure silane and subsequent evaporation of atomic silicon and hydrogen. These evaporated species (primarily) induce a‐Si:H growth on nearby substrates which are temperature controlled using a novel substrate holder. The light and dark conductivities, optical band gap, deposition rates, and light‐soaking effects of preliminary films are reported. The decomposition‐evaporation process has been examined using a mass spectrometer to directly detect the decomposition rate and the evaporated radical species. Based on this data and other information, a simplified model for the deposition process is suggested. The excellent film quality and the attributes of the deposition process make this technique, which was originally suggested by Wiessman, viable for the fast rate, large‐area deposition of a‐Si:H for solar cells and other applications.

195 citations