Browsing by Author "Samukawa, Seiji"

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50% Efficiency Intermediate Band Solar Cell Design Using Highly Periodical Silicon Nanodisk Array
(2012)
Hu, Weiguo
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Igarashi, Makoto
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Lee, Ming-Yi
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Li, Yiming
;
Samukawa, Seiji
A high-quality Si nanodisk superlattice is fabricated by our top-down process. For the first time, a 3D finite element method (FEM) is developed to calculate energy band structure, optical and electrical properties, as well as the intermediate band solar cell (IBSC) operation for the realistic structure. Both the experiments and simulations reveal that miniband formation enhances the optical and electrical collections. Consequently, detailed electronic structure and conversion efficiency are examined to guide optimal design of minibands. A theoretically predicted maximal efficiency of the explored Si nanodisk superlattice is 50.3%, which is promising, compared with well-known complicated Si tandem solar cells.
AlGaN/GaN HEMTs With Damage-Free Neutral Beam Etched Gate Recess for High-Performance Millimeter-Wave Applications
(2016-11)
Lin, Yen-Ku
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Noda, Shuichi
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Lo, Hsiao-Chieh
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Liu, Shih-Chien
;
Wu, Chia-Hsun
The electrical performances of gate-recessed AlGaN/GaN high-electron mobility transistors (HEMTs) fabricated using the damage-free neutral beam etching (NBE) method are demonstrated. The NBE method could eliminate the plasma-induced defects generated by irradiating ultraviolet/VUV photons in the conventional inductively coupled plasma reactive ion etching method. The AlGaN/GaN HEMT device fabricated using the new gate recess process exhibited superior electrical performances, including a maximum drain current density (I-DS,I-max) of 1.54 A/mm, low 1/f noise, a current-gain cutoff frequency (f(T)) of 153 GHz, a maximum frequency of oscillation (f(MAX)) of 167 GHz, and a minimum noise figure (NFmin) of 3.28 dB with an associated gain (G(AS)) of 5.06 dB at 54 GHz. Such superior characteristics confirm the inherent advantages of adopting the damage-free NBE process in fabricating GaN devices for millimeter-wave applications.
AlGaN/GaN HEMTs With Damage-Free Neutral Beam Etched Gate Recess for High-Performance Millimeter-Wave Applications (vol 37, pg 1395, 2016)
(2017-01)
Lin, Yen-Ku
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Noda, Shuichi
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Lo, Hsiao-Chieh
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Liu, Shih-Chien
;
Wu, Chia-Hsun
AlGaN/GaN HEMTs With Damage-Free Neutral Beam Etched Gate Recess for High-Performance Millimeter-Wave Applications (vol 37, pg 1395, 2016)
(2017-01)
Lin, Yen-Ku
;
Noda, Shuichi
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Lo, Hsiao-Chieh
;
Liu, Shih-Chien
;
Wu, Chia-Hsun
Atomic layer defect-free etching for germanium using HBr neutral beam
(2019-09-01)
Fujii, Takuya
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Ohori, Daisuke
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Noda, Shuichi
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Tanimoto, Yosuke
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Sato, Daisuke
The authors developed extremely selective etching for making an atomically flat, defect-free germanium fin (Ge Fin) structure. The etching uses a hydrogen bromide (HBr) neutral beam (NB), and they investigated the etching reaction differences between the HBr NB and a Cl-2 NB. No sidewall etching by HBr NB occurred at 90 degrees C, although that by Cl-2 NB occurred at more than 90 degrees C. This was due to the different boiling points of GeBr4 and GeCl4 as the reacted layer was formed by NB irradiation on the Ge surface. As a result, the Ge sidewall etching by Cl-2 NB occurred above 90 degrees C, whereas that by HBr NB did not occur at 90 degrees C. Additionally, nonvolatile bromide protected layers, such as GeBr4 and SiBrxOy, were deposited on the Ge sidewall and the SiO2 top surface in case of using HBr, respectively. Then, the authors succeeded in fabricating the atomically flat, defect-free Ge Fin structure with the extremely selective HBr NB etching. This result shows that HBr NB can more precisely achieve sub-10-nm scale atomic layer Ge etching for 3D Fin-type MOSFETs.
Atomic layer germanium etching for 3D Fin-FET using chlorine neutral beam
(2019-03-01)
Ohori, Daisuke
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Fujii, Takuya
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Noda, Shuichi
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Mizubayashi, Wataru
;
Endo, Kazuhiko
In case of using pure chlorine chemistry, Ge etching reactivity is three times higher than Si etching reactivity because of the larger lattice spacing in Ge. As a result, during the chlorine plasma etching of a Ge Fin structure, there are serious problems such as a large side-etching and large surface roughness on the Ge sidewall. Conversely, the authors found that several-ten nanometer-width Ge Fin structures with defect-free, vertical, and smooth sidewalls were successively delineated by chlorine neutral beam etching. Based on these results, the problems caused by chlorine plasma etching are considered to be due to the enhancement of chemical reactivity caused by defect on the sidewall with the irradiation of ultraviolet/vacuum ultra violet (UV/VUV) photons. Namely, it is clarified that the neutral beam etching could achieve real atomic layer etching by controlling the defect without any UV/VUV photons on the sidewall surface for future nanoscale Ge Fin structures. Published by the AVS.
Contact Engineering of Trilayer Black Phosphorus With Scandium and Gold
(2019-01-01)
Tsai, Yi-Chia
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Magyari-Kope, Blanka
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Li, Yiming
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Samukawa, Seiji
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Nishi, Yoshio
High contact resistance keeps black phosphorus (BP) from fully wielding its excellent material property. Using first-principles calculations, we analyze the interfacial binding behavior and the impact of binding on the other layers of a trilayer BP. We found that the interfacial charge density and charge transfer of Scandium (Sc)-contacted trilayer BP are 2.67 and 3.29 times greater than Au-contacted trilayer BP, respectively. Moreover, the interfacial tunneling barrier height and width of Sc-contacted trilayer BP are 0 eV and 1.851 angstrom, which are significantly smaller than that of 5.1 eV and 2.447 angstrom observed in Au-contacted trilayer BP. All these facts suggest a strong bonding and efficient carrier transmission between Sc contact and trilayer BP substrate. Therefore, we conclude that the Sc electrode can lead to a superior performance that is consistent with the experiment.
Design and Simulation of High Performance Lattice Matched Double Barrier Normally Off AlInGaN/GaN HEMTs
(2020-01-01)
Shrestha, Niraj Man
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Li, Yiming
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Chen, Chao-Hsuan
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Sanyal, Indraneel
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Tarng, Jenn-Hawn
A novel lattice matched double barrier Al0.72In0.16Ga0.12N/Al0.18In0.04Ga0.78N/GaN normally-off high electron mobility transistor (HEMT) is designed and simulated by solving a set of thermodynamic transport equations. Using the experimentally calibrated physical models with bearing mobility degradation by surface roughness in account, the recess gate and double barrier of the proposed device achieves a maximum drain current density (I-D,I-max) of 1149 mA/mm and a maximum transconductance (g(m,max)) of 358 mS/mm with a positive threshold voltage (Vth) of 0.2 V. The small polarization charge of first barrier is responsible for positive Vth. I-DS,I-max in the double barrier HEMT at high gate bias condition is due to injection of electrons from upper 2DEG which is almost impossible at lower gate voltage because of insufficient energy to cross the barrier. The injection of electrons is further supported by the second peak in the g(m) curve at low gate bias V-G = 1V. The outcome of this study suggests that the proposed device will be beneficial for high-frequency and high-power electronic applications.
Design and Simulation of Intermediate Band Solar Cell With Ultradense Type-II Multilayer Ge/Si Quantum Dot Superlattice
(2017-11-01)
Tsai, Yi-Chia
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Lee, Ming-Yi
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Li, Yiming
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Samukawa, Seiji
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資訊工程學系
We studied the miniband dependence on the structural parameters and shape in type-II multilayer germanium (Ge)/silicon (Si) quantum dot superlattice (QDSL) solar cell. A maximum tunable range of ground-state energy is 19% by tuning layer distance down to 0.5 nm, whereas 24.5% is achieved by adjusting the horizontal dot-to-dot spacing down to 0.3 nm. The reduction of effective bandgap is severe for cylindrical QDs than ellipsoidal and conical QDs in the ultradense QDSL, thus leading to a relatively lower conversion efficiency. On average, the thickness of QD shows a negative correlation to conversion efficiency. We observed a high conversion efficiency of 27.22% in a bilayer conical QDSL under an AM1.5 spectral irradiance and one sun illumination.
Design and Simulation of Si/SiC Quantum Dot Superlattice Solar Cells with Al2O3 Passivation Layer
(2017-01-01)
Tsai, Yi-Chia
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Lee, Ming-Yi
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Li, Yiming
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Samukawa, Seiji
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電信工程研究所
By simultaneously considering the enhancement of quantum confinement on the effective bandgap and minimum transition energy, the silicon (Si)! silicon carbide (SiC) quantum dot superlattice (SiC-QDSL) with aluminum oxide (A1203-QDSL) passivation layer shows the high short-circuit current (J,) of 4.77 mA/cm(2) in theoretical, which agrees with the J, of 4.75 mA/cm(2) obtained in the experiment under an AM1.5 and one sun illumination. Moreover, the reduction of efficiency in an ultra-dense QD configuration can be ameliorated by exploiting the Al2O3 passivation layer. As the result, a high conversion efficiency of 16.3% is optimized by using the QD geometry from experiment and an inter-dot spacing of 0.3 nm.
Diamond-shaped Ge and Ge0.9Si0.1 Gate-All-Around Nanowire FETs with Four {111} Facets by Dry Etch Technology
(2015)
Lee, Yao-Jen
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Hou, Fu-Ju
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Chuang, Shang-Shiun
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Hsueh, Fu-Kuo
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Kao, Kuo-Hsing
We propose a feasible pathway to scale the Ge MOSFET technology by using a novel diamond-shaped Ge and Ge0.9Si0.1 gate-all-around (GAA) nanowire (NW) FETs with four {111} facets. The device fabrication requires only simple top-down dry etching and blanket Ge epitaxy techniques readily available in mass production. The proposed dry etching process involves three isotropic/anisotropic etching steps with different Cl-2/HBr ratios for forming the suspended diamond-shaped channel. Taking advantages of the GAA configuration, favorable carrier mobility of the {111} surface, nearly defect-free suspended channel, and improved dopant activation by incorporating Si, nFET and pFET with excellent performance have been demonstrated, including an I-on/I-off ratio exceeding 10(8), the highest ever reported for Ge-based pFETs.
Effect of ALD-Al2O3 Passivated Silicon Quantum Dot Superlattices on p/i/n(+) Solar Cells
(2017-07-01)
Rahman, Mohammad Maksudur
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Tsai, Yi-Chia
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Lee, Ming-Yi
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Higo, Akio
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Li, Yiming
The photovoltaic (PV) nature of the silicon (Si) quantum dot super lattice (QDSL) is studied with an atomic-layer-deposited aluminum oxide film (ALD-Al2O3) and a conventional sputtered-grown amorphous silicon carbide film (a-SiC). The QDSL structures act as an intermediate layer in a p/i/n(+) Si solar cell. The QDSL consists of 4-nm Si on 2-nm SiC nanodisks (NDs) arrayed in an ALD-Al2O3 and a-SiC passivation matrix. Formation of Si-NDs was confirmed by bright field scanning transmission electron microscope. A significant PV response in generating a high photocurrent density J(sc) of 30.15mA/cm(2), open circuit voltage V-oc of 0.50 V, fill factor FF of 0.61, and efficiency. of 9.12% was observed in ALD-Al2O3/QDSL solar cell with respect to a-SiC/QDSL solar cell with J(sc) of 26.94 mA/cm(2), V-oc of 0.50 V, FF of 0.47, and eta of 6.42%. A wide range of photo-carrier transports by the ALD-Al2O3/QDSL structure is possible in the external quantum efficiency spectra with respect to a-SiC/QDSL solar cell. The enhanced PV performance of the QD solar cells was clarified in terms of simulating the absorption contributions for all possible transitions in the nanostructure with different passivation films.
Electrical Characteristic of AlGaN/GaN High-Electron-Mobility Transistors With Recess Gate Structure
(2019-04-01)
Shrestha, Niraj Man
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Li, Yiming
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Suemitsu, Tetsuya
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Samukawa, Seiji
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交大名義發表
AlGaN/GaN high-electron-mobility transistors (HEMTs) with nonrecess and recess gates are simulated by solving a set of drift-diffusion equations for electrostatic potential and electron-hole concentrations with self-heating model. The approach is first calibrated for both HEMT devices with experimentally measured data, to provide the best accuracy of the simulation. Recess gate device suffers from high potential to the channel, increased parasitic resistances, and deep level traps in barrier due to surface roughness. In addition, selective thinning of the barrier and increase parasitic resistance results in 17% reduction on the carrier concentration. The carrier mobility degradation due to surface roughness and electron velocity lessen due to high electric field result shrinkage of current density with considerable shift of the threshold voltage toward positive value. Even though transconductance does not seems to be remarkably changed for 3-nm recess gate, its value increases on deeper recess. This paper reveals that surface roughness is crucial issue that has dominant role behind the low current density in the recess gate structure. The detail physical understanding of the recess technology will be helpful to minimize the performance deterioration of the explored devices.
Enhancement-mode AlGaN/GaN MIS-HEMTs with Low Threshold Voltage Hysteresis Using Damage-free Neutral Beam Etched Gate Recess
(2016)
Lin, Yen-Ku
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Noda, Shuichi
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Lee, Ruey-Bor
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Huang, Chia-Ching
;
Quang Ho Luc
An enhancement- mode AlGaN/GaN MIS-HEMTs with low threshold voltage hysteresis using damage-free neutral beam etched (NBE) gate recess is reported. The NBE can eliminate the plasma-induced defects that generated by irradiating UV/VUV photons as encounted in the conventional inductively coupled plasma-reactive-ion etching (ICP-RIE). Combining the new gate recess process and PEALD-AlN interfacial passivation layer, the Al2O3/AlGaN/GaN enhancement- mode HEMT device shows a threshold voltage of 1.5 V and a current density of 449 mA/mm, and the three-terminal breakdown voltage was 432 V. The device also shows small hysteresis in threshold voltage at stable I-V curve.
Fabrication of InGaN/GaN Nanodisk Structure by using Bio-template and Neutral Beam Etching Process
(2015)
Lai, Yi-Chun
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Higo, Akio
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Lee, Chang Yong
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Thomas, Cedric
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Tanikawa, Tomoyuki
Quantum dot optoelectronic devices are very attractive for their low power consumption, temperature stability, and high-speed modulation. We developed a defect-less, top-down fabrication process for sub-12-nm diameter InGaN quantum nanodisks (NDs) embedded in GaN barrier by using a combination of a bio-template and neutral beam etching. We have achieved high density of 2.6 x 10(11) cm(-2) with 6-nm in diameter and 15-nm-high nanopillars.
High Performance Poly Si Junctionless Transistors with Sub-5nm Conformally Doped Layers by Molecular Monolayer Doping and Microwave Incorporating CO2 Laser Annealing for 3D Stacked ICs Applications
(2015)
Lee, Yao-Jen
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Cho, Ta-Chun
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Sung, Po-Jung
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Kao, Kuo-Hsing
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Hsueh, Fu-Kuo
A junctionless (JL) fin thin film transistor (FinTFT) with a novel shell doping profile (SDP) formed by a damage-free conformal molecular monolayer doping (MLD) method and a combination of microwave annealing (MWA) and CO2 laser spike annealing (COLSA) is demonstrated and studied. MWA drives in and partially activates the MLD dopants; the resultant SDP features an ultra-shallow depth (< 5nm) and an abrupt steepness (< 0.8 nm/dec). The dopant activation of the devices experienced MLD and MWA is further enhanced by the nonmelting COLSA without dopant diffusion, and which can also avoid fin deformation and recover surface defects left by fin patterning. Thanks to the enhanced dopant activation by COLSA, the SDP-FinTFTs overall exhibit better performance than the SDP-FinTFTs without COLSA and the conventional implanted (imp) FinTFTs in terms of subthreshold swing (S.S.), on-currents (I-on by 160% compared to the SDP-FinTFTs without COLSA) and on/off current ratio (I-on/I-off > 10(7)) for 3D stacked ICs applications. Our results reveal the potential of the proposed SDP formed by MLD, MWA and COLSA enabling a JLFinTFT showing excellent performance.
High-Performance GaN MOSHEMTs Fabricated With ALD Al2O3 Dielectric and NBE Gate Recess Technology for High Frequency Power Applications
(2017-06-01)
Lin, Yen-Ku
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Noda, Shuichi
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Huang, Chia-Ching
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Lo, Hsiao-Chieh
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Wu, Chia-Hsun
High-performance GaN metal-oxidesemi-conductor high-electron-mobility transistors (MOSHEMTs) using Al2O3 gate dielectric deposited by atomic layer deposition (ALD) and damage-free neutral beam etch (NBE) gate recess process for millimeter-wave power applications are demonstrated. The high-quality ALD Al2O3 reduces the gate leakage current of the device and the NBE method eliminates the plasma-induced defects in the nitride materials. The MOSHEMT device fabricated exhibits a high maximum drain current density (I-DS,I-max ) of 1.65 A/mm and a high peak extrinsic transconductance (g(m.ext) ) of 653 mS/mm. The MOSHEMT device also demonstrates excellent RF performances, including f(T)/f(MAX) = 183/191 GHz, NFmin = 2.56 dB with G(AS) = 5.61 dB at 54 GHz, and an output power density of 2.7 W/mm associated with a power-added efficiency of 20.9% and a linear power gain of 9.4 dB at 38 GHz. To the best of our knowledge, the noise performance at 54 GHz is the best reported so far for the AlGaN/GaN HEMTs.
Impact of silicon quantum dot super lattice and quantum well structure as intermediate layer on p-i-n silicon solar cells
(2016-06)
Rahman, Mohammad Maksudur
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Lee, Ming-Yi
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Tsai, Yi-Chia
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Higo, Akio
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Sekhar, Halubai
The photovoltaic effect of the silicon (Si)/silicon carbide (SiC) quantum dot super lattice (QDSL) and multi-quantum well (QW) strucutres is presented based on numerical simulation and experimental studies. The QDSL and QW structures act as an intermediate layer in a p-i-n Si solar cell. The QDSL consists of a stack of four 4-nm Si nano disks and 2-nm SiC barrier layers embedded in a SiC matrix fabricated with a top-down etching process. The Si nano disks were observed with bright field-scanning transmission electron microscopy. The simulation results based on the 3D finite element method confirmed that the quantum effect on the band structure for the QDSL and QW structures was different and had different effects on solar cell operation. The effect of vertical wave-function coupling to form a miniband in the QDSL was observed based on the solar-cell performance, showing a dramatic photovoltaic response in generating a high photocurrent density J(sc) of 29.24mA/cm(2), open circuit voltage V-oc of 0.51V, fill factor FF of 0.74, and efficiency eta of 11.07% with respect to a i-QW solar cell with J(sc) of 25.27mA/cm(2), V-oc of 0.49V, FF of 0.69, and eta of 8.61% and an i-Si solar cell with J(sc) of 27.63mA/cm(2), V-oc of 0.55V, FF of 0.61, and eta of 10.00%. A wide range of photo-carrier transports by the QD arrays in the QDSL solar cell is possible in the internal quantum efficiency spectra with respect to the internal quantum efficiency of the i-QW solar cell. Copyright (C) 2015 John Wiley & Sons, Ltd.
Impacts of plasma-induced damage due to UV light irradiation during etching on Ge fin fabrication and device performance of Ge fin field-effect transistors
(2017-02-01)
Mizubayashi, Wataru
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Noda, Shuichi
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Ishikawa, Yuki
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Nishi, Takashi
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Kikuchi, Akio
We investigated the impacts of plasma-induced damage due to UV light irradiation during etching on Ge fin fabrication and the device performance of Ge fin field-effect transistors (Ge FinFETs). UV light irradiation during etching affected the shape of the Ge fin and the surface roughness of the Ge fin sidewall. A vertical and smooth Ge fin could be fabricated by neutral beam etching without UV light irradiation. The performances of Ge FinFETs fabricated by neutral beam etching were markedly improved as compared to those of Ge FinFETs fabricated by inductively coupled plasma etching, in which the UV light has an impact. (C) 2017 The Japan Society of Applied Physics
Low resistive InGaN film grown by metalorganic chemical vapor deposition
(2020-01-01)
Shrestha, Niraj Man
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Chauhan, Prerna
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Wong, Yuen-Yee
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Li, Yiming
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Samukawa, Seiji
Indium gallium nitride (InGaN) samples were grown on sapphire substrate with low temperature GaN buffer by metalorganic chemical vapor deposition (MOCVD) under varying growth conditions, such as temperature, pressure and ammonia flow. Although high indium composition is considered as indispensable parameter for sheet carrier concentration (n(s)) and low sheet resistance (R-s), our outcomes disclose that higher indium composition in InGaN film doesn't always have high n(s) and low R-s. Acceptor nature of carbon related defects, a major trapping sites for electrons, plays a crucial role to limit the carrier concentrations in the InGaN specially grown at low pressure, low temperature and low ammonia flow. Furthermore, study of metal contacts deposited on the grown samples by transmission line method (TLM) shows that carrier concentration is the most important factor to obtain low contact resistance. The measured contact resistance for the sample with 4.5x 10(16) cm(2) carrier concentration is 0.13 Omm which is among the lowest contact resistance for GaN based materials grown by MOCVD. This proves that the use of InGaN in source and drain contact region can surpassingly reduce contact resistance and significantly improve device performance of AlGaN/GaN device.