The Experts below are selected from a list of 852 Experts worldwide ranked by ideXlab platform
Hyunsoo Kim - One of the best experts on this subject based on the ideXlab platform.
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carrier transport mechanism of mo contact to amorphous hafnium indium zinc oxides
Physica Status Solidi (a), 2014Co-Authors: Seongjun Kim, Kyoungkook Kim, Youngun Gil, Kwangsoon Ahn, Hyunsoo KimAbstract:We investigated the carrier transport mechanism of Mo contacts to amorphous hafnium indium zinc oxides (a-HIZO). As-deposited Mo exhibited nearly ohmic behavior, while the thermal annealing improved the ohmic contact significantly, i.e. the specific contact resistance was 1.9 × 10−1, 4.3 × 10−3, and 1.5 × 10−3 Ω cm2 for the as-deposited, 200 and 400 °C-annealed condition, respectively. The ohmic mechanism of as-deposited Mo contact might be attributed to the barrier inhomogeneity and/or to the trap-assisted tunneling. For the annealed contact, the carrier transport could be explained by thermionic field emission model, yielding a tunneling parameter of 57 meV and a Schottky barrier height of 0.82 eV, i.e. the ohmic behavior is due to the tunneling through thin barrier.
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s parameter and perfect pinning of the fermi level at nonpolar 11 20 a plane p gan surfaces
Applied Physics Letters, 2012Co-Authors: Yun Ju Choi, Keun Man Song, Hyunsoo KimAbstract:We investigated the Schottky barrier height and S-parameter at nonpolar (11-20) a-plane p-GaN surfaces by using Schottky diodes fabricated with various metals, including Ti, Cu, Ni, and Pt. A barrier inhomogeneity model was used to explain anomalous carrier transport behavior at the nonpolar p-GaN surfaces, yielding the mean barrier heights of 2.01, 1.73, 1.82, and 1.92 eV for the Ti, Cu, Ni, and Pt contacts, respectively. The extracted S-parameter was as low as 0.02, indicating perfect pinning of the surface Fermi level at around 1.9 eV above the valence band.
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carrier transport mechanism at metal amorphous gallium indium zinc oxides interfaces
Applied Physics Letters, 2012Co-Authors: Seongjun Kim, Kyoungkook Kim, Hyunsoo KimAbstract:We report the carrier transport mechanism of Ni/Au Ohmic contacts to amorphous gallium indium zinc oxides. Despite the expected large barrier height, Ohmic contact could be achieved due to the trap-assisted tunneling associated with localized tail states. Upon thermal annealing, the specific contact resistance was further reduced to 3.28 × 10−4 Ωcm2, accompanied by a change in the predominant transport mechanism from trap-limited conduction to degenerate conduction. The Ohmic mechanism could be explained in terms of the thermionic field emission model, yielding a tunneling parameter of 49 meV, a Schottky barrier height of 0.63 eV, and a barrier width of 5.2 nm.
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electrical characteristics of pt schottky contacts fabricated on amorphous gallium indium zinc oxides
Japanese Journal of Applied Physics, 2011Co-Authors: Hyunsoo Kim, Seongjun Kim, Kyoungkook Kim, Sungnam Lee, Kwangsoon AhnAbstract:The electrical characteristics of Pt Schottky diodes fabricated on amorphous gallium indium zinc oxide were investigated. On the basis of Schottky theory with the thermionic emission mode, an effective Schottky barrier height (SBH) of 0.55 eV and an ideality factor of 3.38 were obtained. The anomalously high ideality factor could be attributed to the statistical potential variations of conduction band edges, as evidenced from the distinctive carrier transport through percolation hopping conduction. In this respect, the barrier inhomogeneity model was applied to obtain reasonable Schottky parameters, yielding the mean barrier height of 1.23 eV with a large standard deviation of 192 mV.
Yoshiaki Nakano - One of the best experts on this subject based on the ideXlab platform.
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comparison of electron and hole mobilities in multiple quantum well solar cells using a time of flight technique
IEEE Journal of Photovoltaics, 2015Co-Authors: Kasidit Toprasertpong, Kentaroh Watanabe, Masakazu Sugiyama, Hiromasa Fujii, Shigeo Asahi, Tomoyuki Kada, Takashi Kita, Taizo Tanibuchi, Yoshiaki NakanoAbstract:Understanding of transport dynamics of both electrons and holes in quantum-structure solar cells is essential for their structure design and performance enhancement. By applying our proposed carrier time-of-flight technique on p-on-n and n-on-p configurations, we can separately evaluate electron and hole transport across quantum structures inserted in the i-region of solar cells. Electron and hole behaviors in two sets of InGaAs/GaAsP multiple-quantum-well (MQW) solar cells with different potential barrier heights are investigated in this study. Both types of carriers in In0.21Ga0.79As/GaAs0.75P0.25 MQWs show faster averaged velocities by an order of magnitude than those in In0.21Ga0.79As/GaAs0.59P0.41 MQWs, which have higher potential barriers. Within the same MQW structure, the measured values of electron and hole averaged velocities are very close to each other. This results in the same order of effective mobilities of electrons and holes and the similar tendency of cell performance in p-on-n and n-on-p MQW solar cells. Holes in high-barrier InGaAs/GaAsP MQWs show nonlinear mobility, suggesting that a careful design of high-barrier MQWs is required to avoid the hole bottleneck and enhance charge carrier collection.
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effect of barrier thickness on carrier transport inside multiple quantum well solar cells under high concentration illumination
IEEE Journal of Photovoltaics, 2015Co-Authors: Warakorn Yanwachirakul, Kentaroh Watanabe, Masakazu Sugiyama, Hiromasa Fujii, Kasidit Toprasertpong, Yoshiaki NakanoAbstract:Carrier transport inside InGaAs/GaAs/GaAsP multiple quantum well (MQW) solar cells was discussed under high-concentrated sunlight illumination up to 338 suns. Current–voltage (I–V) characteristic curves for a GaAs reference cell and MQW cells with GaAsP barrier thickness of 2, 4, and 6 nm were investigated under dark and high-concentration illumination. Carrier collection efficiency (CCE) was estimated by net photocurrent, which is the difference between illuminated current and dark current density at each bias voltage normalized by the value at the saturated point. For the 2-nm barrier, CCE exhibited almost no degradation compared with the GaAs reference cell. On the other hand, CCE for the 6-nm barrier degraded with forward biases as the sunlight concentration ratio increased. The degradation in CCE under a high-concentration ratio is shown to be the result of carrier accumulation in quantum wells. Thin barriers seemed to eliminate such accumulation with the help of the carrier tunneling effect through the barriers.
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strain effect for different phosphorus content of ingaas gaasp super lattice in gaas p i n single junction solar cell
Journal of Crystal Growth, 2014Co-Authors: Kentaroh Watanabe, Yunpeng Wang, Hassanet Sodabanlu, Masakazu Sugiyama, Yoshiaki NakanoAbstract:Abstract The GaAs p–i–n single junction solar cell with InGaAs/GaAsP super-lattice (SL) in the i-region was fabricated by metal organic vapor phase epitaxy (MOVPE). Using the in situ wafer curvature monitoring, a series of SL solar cell samples with different phosphorus composition in the barrier GaAsP layer was evaluated the accumulated strain during MOVPE growth. The sample with larger phosphorus content in GaAsP barrier layer reduced total strain accumulation, resulted in improved solar cell performance regardless to the higher potential barrier. This result indicated the about 3-nm thick barrier is sufficiently thin for carrier extraction by assisting the tunneling effect. Furthermore, the accumulated strain during MOVPE growth of SL deteriorate solar cell.
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strain effect for different phosphorus content of ingaas gaasp super lattice in gaas p i n single junction solar cell
Journal of Crystal Growth, 2014Co-Authors: Kentaroh Watanabe, Yunpeng Wang, Hassanet Sodabanlu, Masakazu Sugiyama, Yoshiaki NakanoAbstract:Abstract The GaAs p–i–n single junction solar cell with InGaAs/GaAsP super-lattice (SL) in the i-region was fabricated by metal organic vapor phase epitaxy (MOVPE). Using the in situ wafer curvature monitoring, a series of SL solar cell samples with different phosphorus composition in the barrier GaAsP layer was evaluated the accumulated strain during MOVPE growth. The sample with larger phosphorus content in GaAsP barrier layer reduced total strain accumulation, resulted in improved solar cell performance regardless to the higher potential barrier. This result indicated the about 3-nm thick barrier is sufficiently thin for carrier extraction by assisting the tunneling effect. Furthermore, the accumulated strain during MOVPE growth of SL deteriorate solar cell.
De Vries H. W. - One of the best experts on this subject based on the ideXlab platform.
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The role of carrier gas flow in roll-to-roll AP-PECVD synthesized silica moisture barrier films
Surface and Coatings Technology 339 20-26, 2018Co-Authors: Meshkova A. S., Elam F. M., Starostin S. A., M. C. M. Van De Sanden, De Vries H. W.Abstract:Moisture barrier films are deposited on a polymer foil by roll-to-roll Atmospheric Pressure Plasma Enhanced CVD reactor using a N2, O2, TEOS gas mixture. The film microstructure and permeation properties are studied as a function of the carrier gas flow rate with both static and dynamic film transport. The microstructure is analyzed by spatially resolved attenuated total reflectance (ATR)-FTIR and correlated with the vertical density gradient obtained in the dynamic films and the moisture barrier performance. It is shown that by varying the carrier gas flow rate the vertical density gradient, or the network porosity, can be tuned by governing the convective transport inside the reactor consequently densifying the inorganic film at fixed energy cost (i.e. Yasuda parameter) of the process. Moreover, adopting the bilayer architecture allows to achieve the same moisture barrier properties of 2 · 10−3 g·m−2·day−1 (40 °C, 90% RH) at only half the film thickness of a single layer barrier films, which consequently leads to a throughput increase of almost two times.
Yonghang Zhang - One of the best experts on this subject based on the ideXlab platform.
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ultralow interface recombination velocity 1 cm s at cdte mgxcd _ 1 hbox xte heterointerface
IEEE Journal of Photovoltaics, 2017Co-Authors: Xinhao Zhao, Shi Liu, Calli M Campbell, Maxwell B Lassise, Zhao Yuan, Yonghang ZhangAbstract:The interface recombination velocity (IRV) at the interfaces in CdTe/Mg x Cd ${}_{1\hbox{-}}$ x Te double heterostructures (DHs) is studied using time-resolved photoluminescence. It is found that both thermionic emission and tunneling effects can cause photogenerated carrier loss over or through the Mg x Cd ${}_{1\hbox{-}}$ x Te barriers, either due to the low barrier potential or the thin barrier thickness. Thus, carrier lifetime measurements reveal only an effective IRV. The thermionic emission induced interface recombination can be distinguished by conducting temperature-dependent carrier lifetime measurements, and the tunneling induced IRV can be quantified by comparing samples with different barrier thicknesses. When both thermionic emission and tunneling effects are suppressed or even eliminated, the actual IRV (due to the recombination at the DH interface trap states) is measured to be ∼1 cm/s, with a very long carrier lifetime of 3.6 μ s achieved in the DHs.
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ultralow interface recombination velocity 1 cm s in cdte mg x cd 1 x te double heterostructures
Photovoltaic Specialists Conference, 2016Co-Authors: Xinhao Zhao, Shi Liu, Calli M Campbell, Yuan Zhao, Maxwell B Lassise, Yonghang ZhangAbstract:CdTe/Mg x Cd 1−x Te double heterostructures (DHs) grown on InSb (001) substrates using molecular beam epitaxy have demonstrated very long carrier lifetime and low interface recombination velocity (IRV) due to the effective carrier confinement and surface passivation provided by Mg x Cd 1−x Te. However, both thermionic emission and tunneling effects can cause carrier loss over or through the Mg x Cd 1−x Te barriers when the barrier potential is low or when the barrier is thin. Thus carrier lifetime measurement can only give an effective IRV, which consists of the actual IRV that is purely due to recombination through interface trap states, and carrier loss due to thermionic emission and tunneling. By conducting temperature dependent carrier lifetime measurements, the thermionic emission induced interface recombination can be distinguished. Also by comparing samples with different barrier layer thicknesses, the contribution to effective IRV from tunneling effect can be quantified. When both thermionic emission and tunneling effects are eliminated, the actual IRV is measured to be ∼1 cm/s and a very long carrier lifetime of 3.6 μs is observed.
Meshkova A. S. - One of the best experts on this subject based on the ideXlab platform.
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The role of carrier gas flow in roll-to-roll AP-PECVD synthesized silica moisture barrier films
Surface and Coatings Technology 339 20-26, 2018Co-Authors: Meshkova A. S., Elam F. M., Starostin S. A., M. C. M. Van De Sanden, De Vries H. W.Abstract:Moisture barrier films are deposited on a polymer foil by roll-to-roll Atmospheric Pressure Plasma Enhanced CVD reactor using a N2, O2, TEOS gas mixture. The film microstructure and permeation properties are studied as a function of the carrier gas flow rate with both static and dynamic film transport. The microstructure is analyzed by spatially resolved attenuated total reflectance (ATR)-FTIR and correlated with the vertical density gradient obtained in the dynamic films and the moisture barrier performance. It is shown that by varying the carrier gas flow rate the vertical density gradient, or the network porosity, can be tuned by governing the convective transport inside the reactor consequently densifying the inorganic film at fixed energy cost (i.e. Yasuda parameter) of the process. Moreover, adopting the bilayer architecture allows to achieve the same moisture barrier properties of 2 · 10−3 g·m−2·day−1 (40 °C, 90% RH) at only half the film thickness of a single layer barrier films, which consequently leads to a throughput increase of almost two times.
