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Hideyo Okushi

Bio: Hideyo Okushi is an academic researcher from Japanese Ministry of International Trade and Industry. The author has contributed to research in topics: Schottky barrier & Amorphous solid. The author has an hindex of 9, co-authored 20 publications receiving 479 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the forward current of all the junctions studied shows voltage and temperature dependence expressed as exp(−ΔEa f/kT) exp(AV), where ΔEa is the diffusion voltage and A is a constant.
Abstract: We have measured C‐V characteristics and temperature dependence of J‐V characteristics of undoped hydrogenated amorphous silicon (a‐Si:H) heterojunctions formed on p‐type crystalline silicon ( p c‐Si) substrates with different resistivities. It has been found that an abrupt heterojunction model is valid for a‐Si:H/p c‐Si heterojunctions, and the electron affinity of a‐Si:H has been estimated as 3.93±0.07 eV from C‐V characteristics. The forward current of all the junctions studied shows voltage and temperature dependence expressed as exp(−ΔEa f/kT) exp(AV), where ΔEa f and A are constants independent of voltage and temperature, being successfully explained by a multitunneling capture‐emission model. The reverse current is proportional to exp(−ΔEar/kT)(VD−V)1/2, where VD is the diffusion voltage and ΔEar is a constant. This current is probably limited by generation‐recombination process.

281 citations

Journal ArticleDOI
TL;DR: In this article, the dark currentvoltage characteristics of p−i−n hydrogenated amorphous silicon diodes with various thicknesses of the intrinsic layer (i−layer) (770-9300 A) were systematically investigated.
Abstract: The dark current‐voltage characteristics of p‐i‐n hydrogenated amorphous silicon diodes with various thicknesses of the intrinsic layer (i‐layer) (770–9300 A) are systematically investigated. The magnitude of the forward current is found to be independent of thickness of the i layer, which is obviously against the simple conventional junction theory. It has been demonstrated through various experiments that the forward current of amorphous p‐i‐n diodes is limited by a layer thinner than 770 A, possibly being the p/i interface or a narrow zone of the i layer.

41 citations

Journal ArticleDOI
TL;DR: The Schottky junction properties become worse with an increase in the density of unepitaxial crystallites (UC) and pyramidal hillocks (PH).
Abstract: Homoepitaxial diamond films with atomically flat surface were reproducibly grown by step–flow mode under the condition of less than 0.1% CH4/H2. Using these diamond films, high-quality Schottky junctions between Al and high-conductivity layer near the surface of the films have been successfully made. At 400 K, the ideality factor and the barrier height of the Schottky junctions, which are defined by the conventional junction theory, estimated from the current–voltage (I–V) characteristics are about 1.1 and 1.5–1.6 eV, respectively. Under the condition of more than 0.1% CH4/H2, however, many unepitaxial crystallites (UC) and pyramidal hillocks (PH) are often formed on the surface of the films which are even mainly grown by the step–flow mode. The Schottky junction properties become worse with an increase in the density of UC and PH. In particular, the increase in the saturation current, which was obtained by extrapolating the straight line to V=0 in a plot of ln I against V, correlated with Schottky barrie...

32 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the current transport mechanisms of amorphous Schottky barrier junctions using both undoped and phosphorus-doped hydrogenated amorphously silicon-germanium alloys (a−Si1−xGex: H) fabricated by rf glow discharges in diode and triode-reactor systems with and without the dilution of hydrogens.
Abstract: The current‐transport mechanisms of amorphous Schottky barrier junctions are investigated using both undoped and phosphorus‐doped hydrogenated amorphous silicon‐germanium alloys (a‐Si1−xGex: H) fabricated by rf glow discharges in diode‐ and triode‐reactor systems with and without the dilution of hydrogens. From the experimental results, the forward‐current mechanisms for amorphous Schottky barrier junctions are generally discussed and classified into three categories: (1) field emission, (2) diffusion‐field emission, and (3) diffusion. The diffusion‐field‐emission model (multistep tunneling through a part of the Schottky barrier) used for the first time in this work can interpret the current‐voltage characteristics and their temperature dependence on amorphous Schottky barrier junctions to a high degree. Moreover, the flow chart proposed here classifies the material quality of amorphous semiconductors according to their junction properties. We concluded that one of the better methods to fabricate high‐qua...

26 citations

Patent
14 Mar 1984
TL;DR: In this paper, an amorphous photovoltaic energy conversion element for use in a solar cell is composed of a first layer formed of a p-type material, a second layer formed by an intrinsic amorphized semiconductor having a potential gradient formed therein and a third layer formed from a metal capable of coming into ohmic contact with the aforementioned intrinsic layer of amorphus semiconductor and exhibiting a lower work function than the intrinsic layer.
Abstract: An amorphous photovoltaic energy conversion element for use in a solar cell is composed of a first layer formed of a p-type material, a second layer formed of an intrinsic amorphous semiconductor having a potential gradient formed therein and a third layer formed of a metal capable of coming into ohmic contact with the aforementioned intrinsic layer of amorphous semiconductor and exhibiting a lower work function than the work function of the intrinsic layer of amorphous semiconductor.

19 citations


Cited by
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Journal ArticleDOI
TL;DR: In this paper, the current losses due to parasitic absorption in the indium tin oxide (ITO) and amorphous silicon (a-Si:H) layers at the front of silicon heterojunction solar cells are isolated and quantified.
Abstract: The current losses due to parasitic absorption in the indium tin oxide (ITO) and amorphous silicon (a-Si:H) layers at the front of silicon heterojunction solar cells are isolated and quantified. Quantum efficiency spectra of cells in which select layers are omitted reveal that the collection efficiency of carriers generated in the ITO and doped a-Si:H layers is zero, and only 30% of light absorbed in the intrinsic a-Si:H layer contributes to the short-circuit current. Using the optical constants of each layer acquired from ellipsometry as inputs in a model, the quantum efficiency and short-wavelength current loss of a heterojunction cell with arbitrary a-Si:H layer thicknesses and arbitrary ITO doping can be correctly predicted. A 4 cm2 solar cell in which these parameters have been optimized exhibits a short-circuit current density of 38.1 mA/cm2 and an efficiency of 20.8%.

486 citations

Journal ArticleDOI
TL;DR: In this article, the surface passivation at the a-Si/c-Si heterointerface realized by Sanyo's successful technologies for fabricating high-quality aSi films and solar cells with low plasma damage processes is investigated.
Abstract: We have achieved a very high conversion efficiency of 21·5% in HIT cells with a size of 100·3 cm2. One of the most striking features of the HIT cell is its high open-circuit voltage Voc, in excess of 710 mV. This is due to the excellent surface passivation at the a-Si/c-Si heterointerface realized by Sanyo's successful technologies for fabricating high-quality a-Si films and solar cells with low plasma damage processes. We have studied ways to treat the surface to produce a good interface throughout our fabrication processes. We have also investigated the deposition conditions of a-Si layers for optimizing the barrier height for the minority carriers in the heterojunction. Our approach for obtaining HIT cells with a high Voc is reviewed here. Copyright © 2005 John Wiley & Sons, Ltd.

269 citations

Patent
29 Apr 2008
TL;DR: In this paper, a front electrode/contact for use in an electronic device such as a photovoltaic device is described, which includes a multilayer coating including at least one transparent conductive oxide (TCO) layer (e.g., of or including a material such as tin oxide, ITO, zinc oxide, or the like).
Abstract: This invention relates to a front electrode/contact for use in an electronic device such as a photovoltaic device. In certain example embodiments, the front electrode of a photovoltaic device or the like includes a multilayer coating including at least one transparent conductive oxide (TCO) layer (e.g., of or including a material such as tin oxide, ITO, zinc oxide, or the like) and/or at least one conductive substantially metallic IR reflecting layer (e.g., based on silver, gold, or the like). In certain example instances, the multilayer front electrode coating may include one or more conductive metal(s) oxide layer(s) and one or more conductive substantially metallic IR reflecting layer(s) in order to provide for reduced visible light reflection, increased conductivity, cheaper manufacturability, and/or increased infrared (IR) reflection capability.

264 citations

Journal ArticleDOI
TL;DR: In this article, the authors confirm that the abruptness of the interface is strongly determined by the annealing process, and that the passivation quality of completely amorphous silicon films can be improved by annaling at temperatures up to 260°C.
Abstract: Intrinsic hydrogenated amorphous silicon films can yield outstanding electronic surface passivation of crystalline silicon wafers. In this letter the authors confirm that this is strongly determined by the abruptness of the interface. For completely amorphous films the passivation quality improves by annealing at temperatures up to 260°C, most likely by film relaxation. This is different when an epitaxial layer has been grown at the interface during film deposition. Annealing is in such a case detrimental for the passivation. Consequently, the authors argue that annealing followed by carrier lifetime measurements allows determining whether the interface is abrupt.

224 citations

Journal ArticleDOI
TL;DR: A review of the dielectric passivation coatings developed in the past two decades using a standardised methodology to characterise the metrics of surface recombination across all techniques and materials is provided in this article.
Abstract: Silicon wafer solar cells continue to be the leading photovoltaic technology, and in many places are now providing a substantial portion of electricity generation. Further adoption of this technology will require processing that minimises losses in device performance. A fundamental mechanism for efficiency loss is the recombination of photo-generated charge carriers at the unavoidable cell surfaces. Dielectric coatings have been shown to largely prevent these losses through a combination of different passivation mechanisms. This review aims to provide an overview of the dielectric passivation coatings developed in the past two decades using a standardised methodology to characterise the metrics of surface recombination across all techniques and materials. The efficacy of a large set of materials and methods has been evaluated using such metrics and a discussion on the current state and prospects for further surface passivation improvements is provided.

213 citations