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Jaewu Choi - One of the best experts on this subject based on the ideXlab platform.
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correlated lateral and vertical transport of large scale Majority Carrier graphene insulator silicon photodiodes
Journal of Materials Chemistry C, 2019Co-Authors: Hongki Park, Yeonsoo Cho, Myeongseop Kim, Jaewu ChoiAbstract:As the size of graphene–silicon (GS) or graphene–insulator–silicon (GIS) junction devices increases, both vertical and lateral transport behaviors interplay with each other. This study shows that the lateral transport behaviors of macroscopically large Majority Carrier GIS photodiodes affect the vertical transport properties and the performance of GIS photodiodes. The correlations between the lateral and vertical transport properties and the performance of large area GIS photodiodes are investigated by the electrode configuration dependent transport behavior and by the position dependent photoresponse. Lateral voltage drops occur due to resistive graphene layers. This causes the voltage across the junction of GIS devices along the vertical direction to vary with the distance from electrodes. As a result, the effective Schottky barrier height (SBH) governing the vertical transport behaviors also depends on the position and increases with the distance from electrodes. Due to the lateral potential distribution and the longer laterally transient time of photogenerated Carriers along the graphene layer, the photoresponse becomes weaker as the distance increases from the electrodes. Graphene was doped and dedoped due to the employed functional PMMA overlayer. The PMMA overlayer acts as a promotion layer for a high photoresponse by capturing the tunneled photogenerated hot Carriers from silicon. The correlation between the vertical and the lateral transport behaviors is analyzed based on the dark and photo current–voltage characteristics and the voltage dependent graphene Fermi level shift, which is also identified with Raman spectroscopy.
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overlayer induced air gap acting as a responsivity amplifier for Majority Carrier graphene insulator silicon photodetectors
Journal of Materials Chemistry C, 2018Co-Authors: Hongki Park, Jaewu ChoiAbstract:Majority Carrier graphene–insulator–silicon (GIS) photodetectors act as photocurrent amplifiers and thus have high potential for various future electro-optic applications requiring their high responsivity, low dark current, high on–off ratio and high detectivity. Further, this study shows that the poly(methyl methacrylate) (PMMA) overlayer on graphene of the Majority Carrier GIS photodiodes causes more than tenfold enhancement of the known photo-responsivities from the previously reported Majority Carrier GIS photodiodes. The PMMA overlayer on graphene is acting as not only a graphene protection layer, but also a hole dopant for graphene and a mechanically stiffer layer allowing an air gap formation between graphene and silicon. These collectively provide another route for the photocurrent amplification of the Majority Carrier GIS photodetectors. As a result, the GIS diode with PMMA shows a responsivity of 95 A W−1 and a detectivity of 2.1 × 1012 cm Hz1/2 W−1 at an optical power density of 35 μW cm−2.
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High Responsivity and Detectivity Graphene-Silicon Majority Carrier Tunneling Photodiodes with a Thin Native Oxide Layer
ACS Photonics, 2018Co-Authors: Hongki Park, Jaewu ChoiAbstract:A photocurrent amplifier operable at low bias voltages with high responsivity and detectivity is highly demanding for various optoelectronic applications. This study shows Majority Carrier graphene-native oxide-silicon (GOS) photocurrent amplifiers complying with the demands. The photocurrent amplification is primarily attributed to the photoinduced Schottky barrier height (SBH) lowering for Majority Carriers. The unavoidably formed thin native oxide layer between graphene and silicon during the wet graphene transfer process plays significant roles in lowering of the dark leakage current as well as photoinduced SBH lowering. As a result, the photocurrent to dark current ratio is as high as ∼12.7 at the optical power density of 1.45 mW cm–2. These GOS devices show a high responsivity of 5.5 AW–1 at an optical power (458 nm in wavelength) of 15 μWcm–2, which corresponds to ∼1400% quantum efficiency. Further the response speed is as fast as a few ten-microseconds. Thus, these GOS Majority Carrier photodiodes...
Olga S. Volkova - One of the best experts on this subject based on the ideXlab platform.
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Majority Carrier type inversion in the fese family and a doped semimetal scheme in iron based superconductors
Superconductor Science and Technology, 2019Co-Authors: Y. A. Ovchenkov, D. A. Chareev, V.a. Kulbachinskii, Vladimir G. Kytin, S.v. Mishkov, Denis E. Presnov, Olga S. VolkovaAbstract:The field and temperature dependencies of the longitudinal and Hall components of resistivity have been studied for high-quality FeSe1–x S x (x up to 0.14) single crystals. A quasiclassical analysis of the experimental data indicates a strong variation of electron and hole concentrations under the studied isovalent substitution and a clear trend towards the Majority Carrier type inversion. On this basis, we propose a 'doped semimetal' scheme for the superconducting phase diagram of the FeSe family, which can probably be applied to other iron-based superconductors. In this scheme, the two local maxima of the superconducting temperature can be associated with the Van Hove singularities of a simplified semi-metallic electronic structure. A multiCarrier analysis of the experimental data also reveals the presence of a tiny and highly mobile electron band for all the samples studied. Substitution for sulfur in the studied range leads to one order decreasing in the density of highly mobile electrons, from 3% to 0.2% of the total Carrier concentration. The mobility of these Carriers does not depend on impurities, which may indicate an enhanced electron–phonon interaction and allows us to consider the highly mobile Carriers as a possible source of unusual acoustic properties of FeSe.
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Majority Carrier type inversion in FeSe family and "doped semimetal" scheme in iron-based superconductors.
arXiv: Superconductivity, 2018Co-Authors: Y. A. Ovchenkov, D. A. Chareev, V.a. Kulbachinskii, Vladimir G. Kytin, S.v. Mishkov, Denis E. Presnov, Olga S. Volkova, A. N. VasilievAbstract:The field and temperature dependencies of the longitudinal and Hall resistivity have been studied for high-quality FeSe${}_{1-x}$S${}_{x}$ (x up to 0.14) single crystals. Quasiclassical analysis of the obtained data indicates a strong variation of the electron and hole concentrations under the studied isovalent substitution and proximity of FeSe to the point of the Majority Carrier-type inversion. On this basis, we propose a `doped semimetal' scheme for the superconducting phase diagram of the FeSe family, which can be applied to other iron-based superconductors. In this scheme, the two local maxima of the superconducting temperature can be associated with the Van Hove singularities of a simplified semi-metallic electronic structure. The multiCarrier analysis of the experimental data also reveals the presence of a tiny and highly mobile electron band for all the samples studied. Sulfur substitution in the studied range leads to a decrease in the number of mobile electrons by more than ten times, from about 3\% to about 0.2\%. This behavior may indicate a successive change of the Fermi level position relative to singular points of the electronic structure which is consistent with the `doped semimetal' scheme. The scattering time for mobile Carriers does not depend on impurities, which allows us to consider this group as a possible source of unusual acoustic properties of FeSe.
Dan Chen - One of the best experts on this subject based on the ideXlab platform.
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applied trace alkali metal elements for semiconductor property modulation of perovskite thin films
Molecules, 2019Co-Authors: Chuangchuang Chang, Jin Cheng, Tao Ling, Dan ChenAbstract:With the rapid consumption of energy, clean solar energy has become a key study and development subject, especially the when new renewable energy perovskite solar cells (PSCs) are involved. The doping method is a common means to modulate the properties of perovskite film. The main work of this paper is to incorporate trace amounts of alkali metal elements into the perovskite layer and observe the effects on the properties of the perovskite device and the Majority Carrier type of the perovskite film. Comparative analysis was performed by doping with Na+, K+, and Rb+ or using undoped devices in the perovskite layer. The results show that the incorporation of alkali metal ions into the perovskite layer has an important effect on the Majority Carrier type of the perovskite film. The Majority Carrier type of the undoped perovskite layer is N-type, and the Majority Carrier type of the perovskite layer doped with the alkali metal element is P-type. The Carrier concentration of perovskite films is increased by at least two orders of magnitude after doping. That is to say, we can control the Majority of the Carrier type of the perovskite layer by controlling the doping subjectively. This will provide strong support for the development of future homojunction perovskite solar cells. This is of great help to improve the performance of PSC devices.
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impact of k doping on modulating Majority charge Carrier type and quality of perovskite thin films by two step solution method for solar cells
THE Coatings, 2019Co-Authors: Yujun Yao, Jin Cheng, Chuangchuang Chang, Tao Ling, Xiaoping Zou, Dan ChenAbstract:Traditional hetero-junction perovskite solar cells are composed of light-absorbing layers, charge Carrier-transporting layers, and electrodes. Recently, a few papers on homo-junction perovskite solar cells have been studied. Here, we studied the effect of K+ doping on TiO2/PbI2 interface quality, perovskite film morphology, photo-physical properties, and Majority Carrier type. In particular, the K+ extrinsic doping can modulate the Majority Carrier type of the perovskite thin film. The study indicated that the interface between the perovskite layer and the TiO2 layer deteriorates with the increase of K+ doping concentration, affecting the electron transport ability from the perovskite film to the TiO2 layer and the photo-physical properties of the perovskite layer by K+ doping. In addition, the Majority charge Carrier type of perovskite thin films can be changed from n-type to p-type after K+ extrinsic doping, and the corresponding hole concentration increased to 1012 cm−3. This approach of modulating the Majority charge Carrier type of perovskite thin film will pave the way for the investigation of perovskite homo-junction by extrinsic doping for solar cells.
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influence of solution deposition process on modulating Majority charge Carrier type and quality of perovskite thin films for solar cells
Materials, 2019Co-Authors: Chuangchuang Chang, Jin Cheng, Tao Ling, Xiaoping Zou, Yujun Yao, Dan ChenAbstract:In the past ten years, extensive research has witnessed the rapid development of perovskite solar cells (PSCs) and diversified preparation processing craft. At present, the most widely used methods of preparing perovskite solar cells are the one-step method and the two-step method. The main work of this paper is to study the effect of the solution deposition process on the quality of perovskite thin films, as well as modulating Majority charge Carrier types. Perovskite film was prepared in air by designing different processes, which were then adequately analyzed with corresponding methods. It was demonstrated that the preparation process plays a crucial role in modulating the type of Majority Carrier and in achieving high-quality perovskite thin film. The one-step prepared perovskite layer is enriched in MA+, leading to a P type Majority Carrier type thin film. The two-step prepared perovskite layer is enriched in Pb2+, leading to a N type Majority Carrier type thin film. In addition, we found that the one-step method caused PbI2 residue due to component segregation, which seriously affects the interface and film quality of the perovskite layer. This work aims to modulate the Majority Carrier type of perovskite film through different preparation processes, which can lay the foundation for the study of homojunction perovskite solar cells to improve the device performance of PSCs.
Hongki Park - One of the best experts on this subject based on the ideXlab platform.
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correlated lateral and vertical transport of large scale Majority Carrier graphene insulator silicon photodiodes
Journal of Materials Chemistry C, 2019Co-Authors: Hongki Park, Yeonsoo Cho, Myeongseop Kim, Jaewu ChoiAbstract:As the size of graphene–silicon (GS) or graphene–insulator–silicon (GIS) junction devices increases, both vertical and lateral transport behaviors interplay with each other. This study shows that the lateral transport behaviors of macroscopically large Majority Carrier GIS photodiodes affect the vertical transport properties and the performance of GIS photodiodes. The correlations between the lateral and vertical transport properties and the performance of large area GIS photodiodes are investigated by the electrode configuration dependent transport behavior and by the position dependent photoresponse. Lateral voltage drops occur due to resistive graphene layers. This causes the voltage across the junction of GIS devices along the vertical direction to vary with the distance from electrodes. As a result, the effective Schottky barrier height (SBH) governing the vertical transport behaviors also depends on the position and increases with the distance from electrodes. Due to the lateral potential distribution and the longer laterally transient time of photogenerated Carriers along the graphene layer, the photoresponse becomes weaker as the distance increases from the electrodes. Graphene was doped and dedoped due to the employed functional PMMA overlayer. The PMMA overlayer acts as a promotion layer for a high photoresponse by capturing the tunneled photogenerated hot Carriers from silicon. The correlation between the vertical and the lateral transport behaviors is analyzed based on the dark and photo current–voltage characteristics and the voltage dependent graphene Fermi level shift, which is also identified with Raman spectroscopy.
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overlayer induced air gap acting as a responsivity amplifier for Majority Carrier graphene insulator silicon photodetectors
Journal of Materials Chemistry C, 2018Co-Authors: Hongki Park, Jaewu ChoiAbstract:Majority Carrier graphene–insulator–silicon (GIS) photodetectors act as photocurrent amplifiers and thus have high potential for various future electro-optic applications requiring their high responsivity, low dark current, high on–off ratio and high detectivity. Further, this study shows that the poly(methyl methacrylate) (PMMA) overlayer on graphene of the Majority Carrier GIS photodiodes causes more than tenfold enhancement of the known photo-responsivities from the previously reported Majority Carrier GIS photodiodes. The PMMA overlayer on graphene is acting as not only a graphene protection layer, but also a hole dopant for graphene and a mechanically stiffer layer allowing an air gap formation between graphene and silicon. These collectively provide another route for the photocurrent amplification of the Majority Carrier GIS photodetectors. As a result, the GIS diode with PMMA shows a responsivity of 95 A W−1 and a detectivity of 2.1 × 1012 cm Hz1/2 W−1 at an optical power density of 35 μW cm−2.
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High Responsivity and Detectivity Graphene-Silicon Majority Carrier Tunneling Photodiodes with a Thin Native Oxide Layer
ACS Photonics, 2018Co-Authors: Hongki Park, Jaewu ChoiAbstract:A photocurrent amplifier operable at low bias voltages with high responsivity and detectivity is highly demanding for various optoelectronic applications. This study shows Majority Carrier graphene-native oxide-silicon (GOS) photocurrent amplifiers complying with the demands. The photocurrent amplification is primarily attributed to the photoinduced Schottky barrier height (SBH) lowering for Majority Carriers. The unavoidably formed thin native oxide layer between graphene and silicon during the wet graphene transfer process plays significant roles in lowering of the dark leakage current as well as photoinduced SBH lowering. As a result, the photocurrent to dark current ratio is as high as ∼12.7 at the optical power density of 1.45 mW cm–2. These GOS devices show a high responsivity of 5.5 AW–1 at an optical power (458 nm in wavelength) of 15 μWcm–2, which corresponds to ∼1400% quantum efficiency. Further the response speed is as fast as a few ten-microseconds. Thus, these GOS Majority Carrier photodiodes...
Todd C. Roggenbauer - One of the best experts on this subject based on the ideXlab platform.
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Substrate Majority Carrier-Induced NLDMOSFET Failure and Its Prevention in Advanced Smart Power IC Technologies
IEEE Transactions on Device and Materials Reliability, 2006Co-Authors: Vishnu K. Khemka, Amitava Bose, Todd C. RoggenbauerAbstract:This paper discusses substrate Majority Carrier conduction and prevention for an n-type lateral double diffused MOSFET (NLDMOSFET) device in Smart Power IC technologies. Substrate Majority Carrier current poses severe electrical and thermal stress for NLDMOSFET devices and causes many system integration issues for advanced Smart Power IC technologies. A single- and multi-iso isolated NLDMOSFET is proposed and experimentally verified to eliminate the problem. Tradeoff between device size, safe operating area (SOA), substrate current, and NLDMOSFET-device power dissipation has been studied. Detailed analysis of device SOA for conventional and isolated devices and techniques to improve the device SOA has also been provided
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Substrate Majority Carrier Induced NLDMOS Failure and Its Prevention in Advanced Smart Power Technologies
2006 IEEE International Reliability Physics Symposium Proceedings, 2006Co-Authors: Vishnu K. Khemka, Amitava Bose, Todd C. RoggenbauerAbstract:This paper discusses substrate Majority Carrier conduction and prevention for a NLDMOS device in smart power technologies. A multi-iso isolated NLDMOS is proposed and experimentally verified to eliminate the problem. Trade-off between device size, Safe Operating Area, substrate current and NLDMOS device power dissipation has been studied.
