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B. Moradi

Bio: B. Moradi is an academic researcher from Iowa State University. The author has contributed to research in topics: Electron cyclotron resonance & Amorphous silicon. The author has an hindex of 4, co-authored 7 publications receiving 42 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the preparation and properties of hydrogenated amorphous silicon (a•Si:H) and polycrystalline Si (poly•Si) films deposited by electron cyclotron resonance (ECR) reactive plasma deposition were described.
Abstract: We describe the preparation and properties of hydrogenated amorphous silicon (a‐Si:H) and polycrystalline Si (poly‐Si) films deposited by electron cyclotron resonance (ECR) reactive plasma deposition. Hydrogen radicals are generated in a physically remote ECR plasma source and are allowed to interact with silane near the growth surface. By controlling the flux of reactive hydrogen species, polycrystalline and amorphous silicon films were systematically grown. Poly‐Si films having large Hall mobilities of 35 cm2/V s were deposited at temperatures as low as 450 °C without subsequent annealing. High‐quality a‐Si:H films were deposited at temperatures as high as 450 °C. Plasma properties near the growth surface were characterized using both optical emission spectroscopy and Langmuir probe techniques.

15 citations

Journal ArticleDOI
TL;DR: In this paper, the authors examine a technique which allows one to determine the Urbach energy of valence band tails and mid-gap defect densities in amorphous silicon (a-Si:H) devices.

12 citations

Journal ArticleDOI
TL;DR: In this article, the growth and properties of high mobility polycrystalline silicon films grown at low temperatures (400-500°C) on amorphous substrates using a controlled reactive plasma beam deposition were reported.
Abstract: We report on the growth and properties of high mobility polycrystalline silicon films grown at low temperatures (400–500 °C) on amorphous substrates using a controlled reactive plasma beam deposition. The technique consists of carefully controlling the H radical flux from an electron cyclotron resonance (ECR) plasma to promote both nucleation and grain boundary passivation during growth. Using electrical and optical spectroscopy of the ECR plasma, we find that the density of H radicals impinging on the surface is one of the most important parameter controlling crystallinity of the film, and that by changing this flux, we can controllably alter the structure of the film from amorphous to polycrystalline. Unlike traditional deposition techniques for polysilicon, which requires either high deposition temperatures (650 °C) or a low temperature deposition followed by a post deposition anneal to achieve good mobilities, our technique produces films with mobilities of the order of 30–40 cm2/V s in as grown films...

8 citations

Proceedings ArticleDOI
29 May 2008
TL;DR: In this paper, the effects of light-induced degradation in material properties of a Si:H p+in+ cell were examined, and it was shown that the increase in defect density upon degradation can lead to a significant decrease in electric field over middle regions of the i layer.
Abstract: We examine the effects of light‐induced degradation in material properties of a‐Si:H upon the device physics of an a‐Si:H p+in+ cell. It is shown that the increase in defect density upon degradation can lead to a significant decrease in electric field over middle regions of the i layer. This decrease is particularly severe under forward bias (near the maximum power point), and can explain the degradation in fill factor of the cell upon light soaking. We show that by using an innovative cell design, with graded gap i layer, we can increase field inthe middle regions, and reduce the degradation in fill factor.

4 citations

Proceedings ArticleDOI
29 May 2008
TL;DR: In this article, the preparation and properties of aSi:H films produced using a remote ECR plasma at low pressures were investigated and compared to glow-discharge produced films.
Abstract: Electron‐cyclotron‐resonance (ECR) plasma offers a potentially better way of controlling the growth chemistry of a‐Si:H. Such control can be expected to improve the microstructure of a‐Si:H, and hence its stability. In this paper, we report on the preparation and properties of a‐Si:H films produced using a remote ECR plasma at low pressures. It is shown that the ECR‐ a‐Si:H films have electronic properties comparable to glow‐discharge produced films. The stability of ECR‐films appears to be superior to glow‐discharge‐films.

3 citations


Cited by
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Journal ArticleDOI
Jatin K. Rath1
TL;DR: In this article, a comprehensive compilation of recent developments in low temperature deposited poly Si films, also known as microcrystalline silicon, is given, where the effect of ions and the frequency of the plasma ignition are discussed in relation to high deposition rate and the desired crystallinity and structure.

202 citations

Journal ArticleDOI
TL;DR: In this paper, the properties of hydrogenated amorphous silicon (a-Si:H) deposited at very high growth rates (6-80 nm/s) by means of a remote H2-SiH4 plasma have been investigated as a function of the H2 flow in the Ar-H2 operated plasma source.
Abstract: The properties of hydrogenated amorphous silicon (a-Si:H) deposited at very high growth rates (6–80 nm/s) by means of a remote Ar–H2–SiH4 plasma have been investigated as a function of the H2 flow in the Ar–H2 operated plasma source. Both the structural and optoelectronic properties of the films improve with increasing H2 flow, and a-Si:H suitable for the application in solar cells has been obtained at deposition rates of 10 nm/s for high H2 flows and a substrate temperature of 400 °C. The “optimized” material has a hole drift mobility which is about a factor of 10 higher than for standard a-Si:H. The electron drift mobility, however, is slightly lower than for standard a-Si:H. Furthermore, preliminary results on solar cells with intrinsic a-Si:H deposited at 7 nm/s are presented. Relating the film properties to the SiH4 dissociation reactions reveals that optimum film quality is obtained for conditions where H from the plasma source governs SiH4 dissociation and where SiH3 contributes dominantly to film ...

106 citations

Journal ArticleDOI
05 Jul 2005
TL;DR: The factors controlling the deposition of a-Si : H by this technique are investigated, and it is shown that control of gas phase reactions between silane and hydrogen species is essential.
Abstract: Electron cyclotron resonance plasma-enhanced chemical vapor deposition (ECR-PECVD) is investigated as a technique for depositing hydrogenated amorphous silicon (a-Si : H) at a temperature of 80/spl deg/C, which is compatible with the use of transparent, plastic substrates. The ECR-PECVD reactor is described and the principles underlying its operation explained. In particular, the factors controlling the deposition of a-Si : H by this technique are investigated, and it is shown that control of gas phase reactions between silane and hydrogen species is essential. High-quality a-Si : H is deposited in a narrow processing window with a photosensitivity greater than 10/sup 6/. Thin-film transistors (TFTs) fabricated at 125/spl deg/C incorporating low-temperature a-Si : H as the channel layer have a switching ratio of almost 10/sup 5/. With further optimization of the other material layers, such TFTs could be used for the active matrix transistors in flexible liquid crystal displays on plastic substrates.

47 citations

Journal ArticleDOI
TL;DR: Amorphous and polycrystalline silicon (poly-Si) films, deposited by an electron cyclotron resonance plasmaenhanced chemical vapor deposition system at 120°C, have been investigated as discussed by the authors.
Abstract: Amorphous and polycrystalline silicon (poly-Si) films, deposited by an electron cyclotron resonance plasma-enhanced chemical vapor deposition system at 120 °C, have been investigated. All films have been grown with either hydrogen or argon dilution. Using the films with the hydrogen dilution, the effect of rf (13.56 MHz) substrate bias has also been studied. Analysis with x-ray diffraction shows that films grown with Ar dilution and no rf bias do not show any crystallinity while the corresponding films deposited with H2 dilution and no rf bias contain a significant amount of the crystalline phase. With only a 3:1 H2 to silane ratio, highly crystallized films can be grown at 120 °C. In the presence of rf (13.56 MHz) substrate bias, there is a decrease of crystallinity in films. It has been found from cross-sectional transmission electron microscopy that films deposited without rf bias develop a very uniform columnar structure whereas films made with rf bias develop a closely packed, continuous but more amo...

45 citations

Book ChapterDOI
17 Jan 2014
TL;DR: In this paper, the basic operation of a basic thin-film silicon solar cell is discussed, and the structure and technology of single-junction cells in the laboratory are discussed.
Abstract: Thin-film silicon exists in different phases, ranging from amorphous via microcrystalline to single crystalline In contrast to the periodic lattice that characterises the crystalline form, there is only very short-range order in amorphous silicon (a-Si:H) The first amorphous silicon layers were deposited in an rf-driven glow discharge using silane This deposition technique is now usually called plasma-enhanced chemical vapour deposition (PECVD) The hot-wire CVD (HWCVD) technique is based on the decomposition of silicon-containing gases at a catalytic hot surface Today many groups study HWCVD thin-film silicon and its alloys for various applications such as solar cells, passivation layers, and thin-film transistors This chapter discusses the basic operation of a basic thin-film silicon solar cell and then presents the thin-film structure and technology It also talks about the status of the technology of single-junction cells in the laboratory

44 citations