33 results on '"Hirotaka Geka"'
Search Results
2. Relationship between transport properties and band diagrams in InAsxSb1−x/Al0.1In0.9Sb quantum wells
- Author
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Takashi Manago, Shuichi Ishida, Hirotaka Geka, and Ichiro Shibasaki
- Subjects
Physics ,QC1-999 - Abstract
The resistivity of InAs0.1Sb0.9/Al0.1In0.9Sb quantum wells (QWs) is much lower than that of InSb/Al0.1In0.9Sb QWs, staying low resistivity even at low temperature. Fundamental difference in low temperature transport properties between InSb/Al0.1In0.9Sb and InAs0.1Sb0.9/Al0.1In0.9Sb QWs was revealed, based on the band diagram calculations of these QWs. Band diagrams of InAsxSb1−x/Al0.1In0.9Sb QWs showed that the energy band of the InAsxSb1−x layer moves downward with increasing As content x. The QW is type I at x equal to 0, becomes type II at x equal to 0.1. The Fermi level (EF) of the InSb QWs lies in the band gap and below apart from the bottom of the conduction band, while EF of the InAs0.1Sb0.9 QWs is above the bottom of the conduction band of the well. The calculated sheet carrier densities are in good agreement with the experimental results. It well explains that the sheet carrier density difference between InSb and InAs0.1Sb0.9 QWs mainly originates from this band diagram difference and the position of EF.
- Published
- 2015
- Full Text
- View/download PDF
3. Transport properties and observation of quantum Hall effects of InAs0.1Sb0.9 thin layers sandwiched between Al0.1In0.9Sb layers.
- Author
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Ichiro Shibasaki, Hirotaka Geka, Shuichi Ishida, Kenichi Oto, Tomoyuki Ishihara, and Takahide Yoshida
- Published
- 2009
- Full Text
- View/download PDF
4. High-efficiency AlInSb mid-infrared LED with dislocation filter layers for gas sensors
- Author
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D. Yasuda, Y. Shibata, Koichiro Ueno, Osamu Morohara, Y. Sakurai, Hirotaka Geka, H. Fujita, and Naohiro Kuze
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010302 applied physics ,Materials science ,business.industry ,02 engineering and technology ,Luminous intensity ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Emission intensity ,Active layer ,law.invention ,Inorganic Chemistry ,Wavelength ,law ,0103 physical sciences ,Materials Chemistry ,Optoelectronics ,Dislocation ,0210 nano-technology ,Absorption (electromagnetic radiation) ,business ,Luminous efficacy ,Light-emitting diode - Abstract
To fabricate low-consumption and high-resolution gas sensors, especially for methane (CH4) gas (which has absorption around wavelength of 3.3 μm), mid-infrared LEDs are required. Accordingly, to reduce Shockley Read Hall recombination and achieve high luminous intensity at 3.3 μm, an AlxIn1-xSb LED with dislocation filter layers was developed. Dislocation density of the active layer was significantly reduced from 3.5 × 108 to 1.1 × 108/cm2, and luminous efficiency was doubled compared to that of conventionally structured LEDs. To our knowledge, emission intensity at 3.3 μm under injection current of 100 mA is the highest of any commercial LEDs.
- Published
- 2019
5. InAsSb photodiodes grown on GaAs substrates for long-wavelength-infrared gas-sensing applications
- Author
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Y. Shibata, K. Kinoshita, M. Suzuki, Osamu Morohara, D. Yasuda, Hirotaka Geka, Y. Sakurai, H. Fujita, and Naohiro Kuze
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Materials science ,Sensing applications ,Infrared ,business.industry ,Condensed Matter Physics ,Electronic, Optical and Magnetic Materials ,Photodiode ,law.invention ,Long wavelength ,law ,Materials Chemistry ,Optoelectronics ,Electrical and Electronic Engineering ,Dislocation ,business - Published
- 2021
6. High detectivity AlInSb mid-infrared photodiode sensors with dislocation filter layers for gas sensing application
- Author
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Koichiro Ueno, Yoshihiko Shibata, Osamu Morohara, Naohiro Kuze, Mitsuhiro Nakayama, Hiromi Fujita, Hirotaka Geka, Yoshiki Sakurai, and Daiki Yasuda
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Materials science ,business.industry ,law ,Filter (video) ,Product (mathematics) ,Mid infrared ,Optoelectronics ,Substrate (electronics) ,Dislocation ,business ,Omega ,Photodiode ,law.invention - Abstract
High detectivity AlInSb mid-infrared photodiode sensor was fabricated on GaAs substrate. By inserting two pairs of 20 nm dislocation filter layers with high Al composition into n-type buffer layer, threading dislocation density was reduced to 1/3 or less. Resulting photodiode sensor showed high resistivity-area product (RA) of $19\ \mathrm{M}\Omega\mu \mathrm{m}^{2}$ and high normal-incidence detectivity of $1.7\times 10^{9}\ \mathrm{cm}\ \surd \mathrm{Hz}/\mathrm{W}$ at $3.3\ \mu \mathrm{m}$ at room temperature. To the best of our knowledge, this photodiode shows the highest performance in highly mismatched alloy system, i.e. AlInSb on GaAs substrate.
- Published
- 2019
7. Realization of high detectivity mid-infrared photodiodes based on highly mismatched AlInSb on GaAs substrates
- Author
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D. Yasuda, Naohiro Kuze, Osamu Morohara, H. Fujita, M. Suzuki, Yoshihiko Shibata, Y. Sakurai, and Hirotaka Geka
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010302 applied physics ,Threading dislocations ,Materials science ,business.industry ,Mid infrared ,General Physics and Astronomy ,Conductance ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Active layer ,Photodiode ,law.invention ,law ,0103 physical sciences ,Optoelectronics ,Dislocation ,0210 nano-technology ,business ,Layer (electronics) ,Realization (systems) - Abstract
We have systematically investigated highly mismatched AlInSb photodiodes grown on GaAs substrates operating in the mid-infrared range. A novel characterization method was introduced to analyze the recombination mechanism within an active layer of the devices, which revealed a high conductance stemming from the leaky behavior of dislocations. The introduction of a dislocation filter layer successfully reduced threading dislocations and improved resistance area product of photodiodes, leading to high detectivity at room temperature.
- Published
- 2021
8. Interfacial trap states and improvement of low-temperature mobility by doping in InSb/AlInSb quantum wells.
- Author
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Takashi Manago, Shuichi Ishida, Hirotaka Geka, and Ichiro Shibasaki
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THERMISTORS ,TEMPERATURE ,THERMAL properties ,THERMODYNAMIC state variables ,HYDRAULIC structures - Abstract
The effect of doping on InSb/Al
0.1 In0.9 Sb quantum wells (QWs) was investigated, and it was found that doping improves the electron mobility at low temperatures and leads to a weaker dependence of the resistivity with temperature. The dependence of the carrier density on the well width revealed trap states at the interfaces of the QW whose sheet density per interface was estimated to be about 4×1010 cm-2 . The low mobility of undoped InSb QWs, in particular, at low temperature seems to have been caused by positively ionized impurity scattering at the interfacial trap states. Doping compensates for the trap states and enhances mobility by suppressing ionized impurity scattering. Thus, intentional doping is necessary for developing high-mobility InSb QW devices. The origin of the trap states is qualitatively discussed. [ABSTRACT FROM AUTHOR]- Published
- 2015
- Full Text
- View/download PDF
9. Low temperature transport property of the InSb and InAsSb quantum wells with Al0.1In0.9Sb barrier layers grown by MBE
- Author
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I. Shibasaki, Takashi Manago, S. Ishida, and Hirotaka Geka
- Subjects
Inorganic Chemistry ,Physics ,symbols.namesake ,Charge-carrier density ,Condensed matter physics ,Electrical resistivity and conductivity ,Fermi level ,Band diagram ,Materials Chemistry ,symbols ,Condensed Matter Physics ,Conduction band ,Quantum well - Abstract
We investigated difference in the transport properties between Al0.1In0.9Sb/InSb and Al0.1In0.9Sb/InAs0.1Sb0.9 quantum wells (QWs). The resistivity of InSb QWs increases exponentially with decreasing temperature, while that of InAs0.1Sb0.9 QWs is much lower than that of InSb QWs, showing low resistivity even at low temperature. Energy band diagram calculations of InAsxSb1−x/Al0.1In0.9Sb quantum wells (QWs) revealed that the bottom of the conduction band of the InAsxSb1−x well moves downward with increasing As content x. The bottom of the InSb QWs lies above the Fermi level (EF), resulting in depletion of the QW, while that in InAs0.1Sb0.9 QWs lies under EF at low temperature. These calculation results support the experimental difference of the resistivity and sheet carrier density between two types of the QWs well.
- Published
- 2015
10. NDIR gas sensing using high performance AlInSb mid-infrared LEDs as light source
- Author
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Hromi Fujita, Osamu Morohara, Edson Gomes Camargo, Koichiro Ueno, Yoshihiko Shibata, Yuji Goda, Hirotaka Geka, and Naohiro Kuze
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010302 applied physics ,Materials science ,business.industry ,Infrared ,Energy conversion efficiency ,Detector ,02 engineering and technology ,engineering.material ,021001 nanoscience & nanotechnology ,01 natural sciences ,law.invention ,Photodiode ,Absorbance ,Coating ,law ,0103 physical sciences ,engineering ,Optoelectronics ,0210 nano-technology ,business ,Optical filter ,Light-emitting diode - Abstract
In this paper, we report the performance of room temperature operated mid-infrared light emitting diode (LED) with an InSb buffer layer and AlInSb active/barrier layers, which showed to be suitable for non-dispersive infrared (NDIR) gas sensing. Characterization of the LED was performed and we found that good carrier confinement and crystalline quality was responsible for its high performance. High efficiency light extraction was obtained by adopting backside emission architecture together with surface roughening treatment and TiO 2 anti-reflection coating. The fabricated AlInSb LED showed 75% higher power conversion efficiency when compared with a commercially available device. The developed LED, together with a commercially available infrared (IR) detector equipped with band-pass optical filter (AK9710, manufactured by Asahi Kasei Microdevices) were coupled into a mirror system forming a light path length of 80 mm, which was tested for CO 2 gas sensing. For a non-absorbing environment, sensor output of 8 nA was obtained by driving the LED with peak current of 100 mA and, by exposing the system at CO 2 concentration of 1000 ppm signal reduction due to absorbance around 12% was obtained.
- Published
- 2017
11. Highdetectivity AlInSb Midinfrared Photodiode Sensors with Dislocation Filter Layers for Gas Sensing
- Author
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Hiromi Fujita, Hirotaka Geka, Naohiro Kuze, Osamu Morohara, Yoshiki Sakurai, Mitsuhiro Nakayama, Yoshihiko Shibata, Daiki Yasuda, and Masaru Suzuki
- Subjects
Materials science ,business.industry ,Graphene ,Surfaces and Interfaces ,Condensed Matter Physics ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,Photodiode ,law ,Filter (video) ,Materials Chemistry ,Optoelectronics ,Electrical and Electronic Engineering ,Dislocation ,business ,Molecular beam epitaxy - Published
- 2019
12. Dislocation reduction in AlInSb mid-infrared photodiodes grown on GaAs substrates
- Author
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T. Yamauchi, T. Nakao, Y. Sakurai, M. Nakayama, Hirotaka Geka, M. Suzuki, H. Fujita, Osamu Morohara, Naohiro Kuze, and Yoshihiko Shibata
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010302 applied physics ,Imagination ,Range (particle radiation) ,Chemical substance ,Materials science ,business.industry ,media_common.quotation_subject ,General Physics and Astronomy ,Strain energy density function ,02 engineering and technology ,021001 nanoscience & nanotechnology ,01 natural sciences ,Photodiode ,law.invention ,Magazine ,law ,0103 physical sciences ,Optoelectronics ,Dislocation ,0210 nano-technology ,business ,Science, technology and society ,media_common - Abstract
We investigated the electrical and optical properties of a highly mismatched AlInSb/GaAs photodiode sensor working in the mid-infrared range at room temperature. A substantial increase in the device performance was achieved by controlling the strain energy density in the dislocation filter layers and barrier layers to reduce the density of threading and interfacial dislocations, respectively. The resulting photodiode showed a high resistance-area product of 0.24 Ω cm2 and a peak detectivity of 2.2 × 109 cm Hz1/2 W–1 at 3.3 μm.We investigated the electrical and optical properties of a highly mismatched AlInSb/GaAs photodiode sensor working in the mid-infrared range at room temperature. A substantial increase in the device performance was achieved by controlling the strain energy density in the dislocation filter layers and barrier layers to reduce the density of threading and interfacial dislocations, respectively. The resulting photodiode showed a high resistance-area product of 0.24 Ω cm2 and a peak detectivity of 2.2 × 109 cm Hz1/2 W–1 at 3.3 μm.
- Published
- 2019
13. Sb irradiation effect on growth of GaAs thin film on Si (111) substrate
- Author
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Yoshitaka Moriyasu, Hirotaka Geka, Osamu Morohara, and Naohiro Kuze
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Diffraction ,congenital, hereditary, and neonatal diseases and abnormalities ,Materials science ,02 engineering and technology ,Substrate (electronics) ,01 natural sciences ,Inorganic Chemistry ,Crystallinity ,0103 physical sciences ,Materials Chemistry ,Surface roughness ,Irradiation ,Thin film ,010302 applied physics ,business.industry ,nutritional and metabolic diseases ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,eye diseases ,Crystallography ,Transmission electron microscopy ,Optoelectronics ,sense organs ,0210 nano-technology ,business ,Molecular beam epitaxy - Abstract
We studied the effect of Sb4 irradiation on the growth of GaAs thin films on Si (111) substrates. GaAs thin films were grown by molecular beam epitaxy (MBE) system with As2 as a source. Sb4 was also supplied during the GaAs growth. We evaluated surface roughness with an atomic force microscope and crystallinity with an X-ray diffraction system. When GaAs is grown without Sb4 irradiation, crystallinity can be improved by subjecting it to high temperatures, although the surface becomes very rough. In contrast, GaAs grown with Sb4 irradiation showed both good crystallinity and a very flat surface. As the growth temperature increased, both crystallinity and surface flatness were improved, probably due to the enhanced migration with two-dimensional growth modes. Furthermore, plan-view observation with a transmission electron microscope (TEM) showed that Sb4 irradiation was very effective for reducing stacking faults.
- Published
- 2013
14. AlInSb Mid-Infrared LEDs of High Luminous Efficiency for Gas Sensors
- Author
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Koichiro Ueno, Hiromi Fujita, Osamu Morohara, Hirotaka Geka, Yoshihiko Shibata, Edson Gomes Camargo, and Naohiro Kuze
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010302 applied physics ,Materials science ,business.industry ,Mid infrared ,02 engineering and technology ,Surfaces and Interfaces ,021001 nanoscience & nanotechnology ,Condensed Matter Physics ,01 natural sciences ,Surfaces, Coatings and Films ,Electronic, Optical and Magnetic Materials ,law.invention ,law ,0103 physical sciences ,Materials Chemistry ,Optoelectronics ,Electrical and Electronic Engineering ,0210 nano-technology ,Luminous efficacy ,business ,Light-emitting diode - Published
- 2018
15. Carrier density dependence of spin–orbit interaction in InAsSb quantum wells
- Author
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Ichiro Shibasaki, N. Nishizako, Hirotaka Geka, S. Ishida, and Takashi Manago
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Physics ,Condensed matter physics ,Magnetoresistance ,Condensed Matter::Other ,Scattering ,Spin–orbit interaction ,Inelastic scattering ,Zero field splitting ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Electronic, Optical and Magnetic Materials ,Condensed Matter::Materials Science ,Electronic band structure ,Rashba effect ,Quantum well - Abstract
We investigated the spin–orbit interaction (SOI) in Al 0.1 In 0.9 Sb/Sn-doped InAs 0.1 Sb 0.9 quantum wells (QWs) with different doping levels using the weak anti-localization effect in the magneto-resistance. The inelastic scattering time is close to the T −1 law predicted theoretically for electron–electron interaction, and the spin–orbit scattering time is temperature independent as expected for the D'yakonov–Perel mechanism. The carrier-density dependence of zero-field spin-splitting energy extracted from the fits of magneto-resistance was examined by the theoretical calculation. The result confirms that the Dresselhaus SOI is much larger than the Rashba SOI in our QWs. The dominance of the Dresselhaus term in SOI originates in the large weight factor of InSb-based alloy.
- Published
- 2010
16. Accumulation of Localized Electrons in Sn Doped InSb/AlxIn1−xSb Quantum Wells
- Author
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Takashi Manago, S. Ishida, N. Nishizako, Ichiro Shibasaki, and Hirotaka Geka
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Physics ,Condensed matter physics ,Magnetoresistance ,Doping ,InSb quntum well ,Spin–orbit interaction ,Electron ,Physics and Astronomy(all) ,Variable-range hopping ,Weak localization ,Weak anti-localization ,Spin-orbit interaction ,Quantum well ,Sheet resistance - Abstract
We examined the role of localized electrons in the accumulation layer of Sn-doped InSb quantum wells (QWs) with various wellwidths ( L w = 15 ∼ 150 nm ) . At liquid He temperatures, the samples with the sheet resistance ρ > ρ c = h / e 2 for L w 30 nm exhibit the variable-range hopping (VRH), while those with ρ ρ c f o r L w > 50 nm exhibit weak localization (WL), where ρ c is the quantum resistance. In particular, a part of the electrons (with density of N str = 8 × 1 0 10 cm − 2 ) from Sn donors are trapped at the interface states at low temperatures below 77 K. In the WL regime, we observed the small positive magnetoresistance (MR) peak arising from the weak anti-localization (WAL) in the presence of spin-orbit interaction (SOI). In contrast to the WAL in WL regime, the low-field MR in the VRH regime remains entirely negative surviving the SOI, indicating that the hopping MR due to the quantum interference (QI) is completely negative regardless of the SOI. This result supports the predictions based on the directed-path approach for forward-scattering paths ignoring the back-scattering return loops for the QI in the VRH.
- Published
- 2010
17. SPIN RESOLVED SUBBAND-LANDAU-LEVEL COUPLING AND ELECTRON-HOLE COUPLING IN <font>InAs</font>/<font>AlGaSbAs</font> QUANTUM WELL
- Author
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Takahide Yoshida, Shuichi Ishida, Kenichi Oto, Hirotaka Geka, and Ichiro Shibasaki
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Physics ,Condensed matter physics ,Quantum spin Hall effect ,Hall effect ,Statistical and Nonlinear Physics ,Electron hole ,Landau quantization ,Quantum Hall effect ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Condensed Matter Physics ,Quantum well ,Spin-½ ,Magnetic field - Abstract
We have investigated the magneto-transport properties in InAs / AlGaSbAs quantum well (QW), where the lattice mismatch is less than 0.5%. In tilted magnetic fields, the spin-resolved subband-Landau-level coupling has been clearly observed in the magneto-resistance due to the large g -factor of this QW. An anomaly in the Hall effect has been observed at high magnetic fields of the filling factor being less than unity, which is caused by the coexistence of electrons and holes in the system.
- Published
- 2009
18. Transport properties of InSb and InAs0.1Sb0.9 thin films sandwiched between Al0.1In0.9Sb layers grown by molecular beam epitaxy
- Author
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Atsushi Okamoto, Ichiro Shibasaki, and Hirotaka Geka
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Electron mobility ,Materials science ,business.industry ,Mineralogy ,Condensed Matter Physics ,Layer thickness ,Lattice mismatch ,Active layer ,Inorganic Chemistry ,Materials Chemistry ,Optoelectronics ,Thin film ,business ,Quantum well ,Molecular beam epitaxy ,Electronic properties - Abstract
InAs 0.1 Sb 0.9 active layers sandwiched between Al 0.1 In 0.9 Sb insulating layers were grown on GaAs(100) substrates by molecular beam epitaxy (MBE) where the InAs 0.1 Sb 0.9 active layers had no lattice mismatch with the Al 0,1 In 0.9 Sb layers. Basic transport properties and electronic properties of the InAs 0.1 Sb 0.9 were studied as functions of InAs 0.1 Sb 0.9 thickness. Very large electron mobility of InAs 0.1 Sb 0.9 active layers and very small thickness dependence at
- Published
- 2009
19. Hall effect and magnetoresistance analysis by electron–hole coexisting model in AlInSb/InAsSb quantum wells
- Author
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Ichiro Shibasaki, Takashi Manago, N. Nisizako, S. Ishida, and Hirotaka Geka
- Subjects
Inorganic Chemistry ,Electron mobility ,Condensed matter physics ,Magnetoresistance ,Hall effect ,Chemistry ,Materials Chemistry ,Electronic structure ,Electron hole ,Electron ,Condensed Matter Physics ,Quantum well ,Molecular beam epitaxy - Abstract
Transport properties were investigated for undoped Al 0.1 In 0.9 Sb/ InAs 0.1 Sb 0.9 quantum wells (QWs), and two-carrier analyses were applied to the magnetic-field variations of the Hall coefficient and magnetoresistance at 77 K. The Hall coefficient increases with magnetic field, which shows coexistence of electrons and holes. This behaviour is similar to AlGaAsSb/ InAs QWs, which have a type-II band structure. Additionally, the Hall coefficient turns to decrease in more than 1 T, and the behaviour was not observed in the deep InAs QWs. This indicated that there are other electrons with different mobility. These are thought to be electrons extended over the QW, accumulated near the hetero-interface, and thermally excited in the barrier layer.
- Published
- 2009
20. Properties of InSb single-crystal thin films sandwiched by Al0.1In0.9Sb layers with 0.5% lattice mismatch grown on GaAs
- Author
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Ichiro Shibasaki, Hiromasa Goto, Kazuo Yoshida, Atsushi Okamoto, Hirotaka Geka, and Satoshi Yamada
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Inorganic Chemistry ,Electron mobility ,Electron density ,Materials science ,Condensed matter physics ,Doping ,Materials Chemistry ,Electron temperature ,Substrate (electronics) ,Thin film ,Condensed Matter Physics ,Single crystal ,Molecular beam epitaxy - Abstract
We studied the properties of InSb single-crystal thin films sandwiched by Al 0.1 In 0.9 Sb layers (with 0.5% lattice mismatch between InSb and Al 0.1 In 0.9 Sb) grown by molecular beam epitaxy on a GaAs substrate. The electron mobility of these InSb thin films was significantly higher and the electron density was very small in thin regions of less than 0.5 μm compared to InSb thin films directly grown on the GaAs substrate. These results mean that the Al 0.1 In 0.9 Sb layers almost eliminated the large lattice mismatch effect observed at the InSb/GaAs hetero-interface. The dependence of electron mobility and electron density on temperature is also discussed with respect to the InSb thickness and Sn doping.
- Published
- 2007
21. Electrical properties of InAs thin films grown directly on GaAs(100) substrates by MBE
- Author
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Ichiro Shibasaki, Atsushi Okamoto, and Hirotaka Geka
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Range (particle radiation) ,Electron mobility ,Electron density ,Materials science ,business.industry ,Doping ,Mineralogy ,Condensed Matter Physics ,Inorganic Chemistry ,Crystal ,Materials Chemistry ,Optoelectronics ,Thin film ,business ,Sheet resistance ,Molecular beam epitaxy - Abstract
It was found that the crystal quality, electron mobility and electron density of InAs single-crystal thin films grown directly on GaAs (1 0 0) substrates have a strong dependence on the film thickness. Moreover, tin doping increased the electron mobility compared to that of undoped InAs thin films. In addition, the tin doping reduced the temperature dependence of electron mobility and electron density of the InAs thin films. It is concluded from these results that tin doping during MBE growth of InAs can produce InAs single-crystal thin films suitable for magnetic sensors with a wide range of operation temperatures.
- Published
- 2005
22. Transport properties of InSb and InAs thin films on GaAs substrates
- Author
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Atsushi Okamoto, Hirotaka Geka, Ichiro Shibasaki, and Kazuo Yoshida
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Electron mobility ,Electron density ,Materials science ,business.industry ,Doping ,Mineralogy ,Condensed Matter Physics ,Inorganic Chemistry ,Charge-carrier density ,Electrical resistivity and conductivity ,Materials Chemistry ,Optoelectronics ,Lamellar structure ,Thin film ,business ,Molecular beam epitaxy - Abstract
The heterointerfaces in InAs and InSb thin films grown on GaAs were found to affect the temperature dependence of the film's electrical properties such as electron mobility, electron density, and resistivity. The InAs and InSb surfaces of the films, which act as heterointerfaces with air, were found to similarly affect the electrical properties. It was found that the electron mobility of both InAs and InSb films grown on GaAs substrates has a three-layer structure.
- Published
- 2005
23. Effects of AlGaAsSb electron supply layer for InGaAs/InAlAs metamorphic HEMTs on GaAs substrate
- Author
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Kazuhiro Nagase, Hirotaka Geka, Satoshi Yamada, Naohiro Kuze, and Masato Toita
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Electron mobility ,Materials science ,business.industry ,Doping ,Heterojunction ,Substrate (electronics) ,High-electron-mobility transistor ,Condensed Matter Physics ,Inorganic Chemistry ,Materials Chemistry ,Optoelectronics ,business ,Layer (electronics) ,Quantum well ,Molecular beam epitaxy - Abstract
We studied the effects of an AlGaAsSb electron supply layer for InGaAs/InAlAs metamorphic high electron mobility transistors (mHEMTs) on GaAs substrate. By implementing an AlGaAsSb electron supply layer, we drastically improved the electron mobility of InGaAs/InAlAs heterostructures for mHEMTs. An AlGaAsSb electron supply layer for InGaAs/InAlAs heterostructures on GaAs substrates promises high-performance mHEMTs with low production cost.
- Published
- 2011
24. Spin–orbit interaction and negative magnetoresistance for localized electrons in InSb quantum wells
- Author
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S. Ishida, Takashi Manago, Hirotaka Geka, Ichiro Shibasaki, and N. Nishizako
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Physics ,Condensed matter physics ,Magnetoresistance ,Silicon on insulator ,Electron ,Spin–orbit interaction ,Condensed Matter Physics ,Variable-range hopping ,Quantum ,Atomic and Molecular Physics, and Optics ,Quantum well ,Sheet resistance ,Electronic, Optical and Magnetic Materials - Abstract
Weak-field magnetoresistance (MR) in the variable-range hopping (VRH) in the presence of spin–orbit interaction (SOI) for 2DEGs at the hetero-interface of InSb quantum wells was examined in view of the quantum interference (QI) effect. Samples with the sheet resistance, ρ > ρ c = h / e 2 , exhibit VRH, while those with ρ ρ c exhibit weak localiz a tion (WL) at low temperatures, where h / e 2 is the quantum resistance. In the WL regime, a positive magnetoresistance (MR) peak due to the weak anti-localization (WAL) with SOI is clearly observed in low magnetic field. In contrast, the low-field hopping MR remains entirely negative surviving the SOI, indicating that the hopping MR due to the QI is completely negative regardless of the SOI. This result supports the predictions based on the directed-path approach for forward-scattering paths ignoring the back-scattering return loops for the QI in the VRH.
- Published
- 2010
25. Transport properties and observation of quantum Hall effects of InAs0.1Sb0.9 thin layers sandwiched between Al0.1In0.9Sb layers
- Author
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S. Ishida, Tomoyuki Ishihara, Takahide Yoshida, Ichiro Shibasaki, Hirotaka Geka, and Kenichi Oto
- Subjects
Electron mobility ,Materials science ,Thin layers ,Condensed matter physics ,Hall effect ,General Engineering ,Quantum Hall effect ,Thin film ,Quantum well ,Molecular beam epitaxy ,Active layer - Abstract
InAs0.1Sb0.9 active layers sandwiched between Al0.1In0.9Sb insulating buffer layers were grown on GaAs (100) substrates by molecular beam epitaxy. The basic transport properties at room temperature and quantum Hall effects at low temperature of the InAs0.1Sb0.9 were studied as a function of InAs0.1Sb0.9 thickness. The electron mobility of the InAs0.1Sb0.9 active layers had a very high value and very small thickness dependence at less than 500nm. The quantum Hall effects of the InAs0.1Sb0.9 were observed at thicknesses 15, 20, 30, 50, 70, and 100nm. The observation of the quantum Hall effect at thickness more than 50nm strongly suggests the existence of two-dimensional electron gas in the InAs0.1Sb0.9 layer sandwiched between Al0.1In0.9Sb layers.
- Published
- 2009
26. [Untitled]
- Author
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Tetsuo Fukase, Kaichiro Chiba, Takayuki Goto, Hirotaka Geka, and Takao Suzuki
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Superconductivity ,Tetragonal crystal system ,Materials science ,Sign reversal ,Condensed matter physics ,Hall effect ,Phase (matter) ,Transition temperature ,Magnetic phase transition ,General Materials Science ,Condensed Matter Physics ,Atomic and Molecular Physics, and Optics ,Structural transformation - Abstract
La-NMR, Hall coefficient and sound velocity have been measured in order to investigate the correlation between the magnetic ordering, the prominent change of transport properties, the suppression of T c and the structural transformation around x∼1/8 in La 1.96−x Y 0.04 Sr x CuO 4. By the substitution of 0.04/2 Y for La-sites, the structural transformation to the low temperature tetragonal phase (LTT) is caused at 57±14 K for samples around x∼0.115. The. prominent decrease of the Hall coefficient followed by the sign reversal and the magnetic ordering are observed around x∼0.115 below temperatures T s and T N, respectively. T s vs x shows a bell shaped curve with the maximum value of 65 K at x∼00115 where most prominent suppression of T c appears. T N shows similar x dependence to T s with the maximum value of 40 K at x∼0.115. The change of the electronic state below T s and the suppression of T c become more prominent and the magnetic ordering is observed more wide range of x under the LTT phase.
- Published
- 1999
27. Real-time observation of rotational twin formation during molecular-beam epitaxial growth of GaAs on Si (111) by x-ray diffraction
- Author
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Yuka Nakata, Kazuma Ikeda, Hirotaka Geka, Yoshitaka Moriyasu, Masamitu Takahasi, Osamu Morohara, Yoshio Ohshita, and Hidetoshi Suzuki
- Subjects
010302 applied physics ,Diffraction ,Materials science ,Silicon ,Nucleation ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,02 engineering and technology ,021001 nanoscience & nanotechnology ,Epitaxy ,01 natural sciences ,lcsh:QC1-999 ,Gallium arsenide ,chemistry.chemical_compound ,Crystallography ,chemistry ,0103 physical sciences ,X-ray crystallography ,0210 nano-technology ,Crystal twinning ,lcsh:Physics ,Stacking fault - Abstract
The formation and evolution of rotational twin (TW) domains introduced by a stacking fault during molecular-beam epitaxial growth of GaAs on Si (111) substrates were studied by in situ x-ray diffraction. To modify the volume ratio of TW to total GaAs domains, GaAs was deposited under high and low group V/group III (V/III) flux ratios. For low V/III, there was less nucleation of TW than normal growth (NG) domains, although the NG and TW growth rates were similar. For high V/III, the NG and TW growth rates varied until a few GaAs monolayers were deposited; the mean TW domain size was smaller for all film thicknesses.
- Published
- 2016
28. Quantum Hall Effect and Spin Resolved Anti-crossing of Landau Levels in AlGaSbAs∕InAs and AlInSb∕InAsSb Quantum Wells
- Author
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Takahide Yoshida, Tomoyuki Ishihara, Kenichi Oto, Shuichi Ishida, Hirotaka Geka, Ichiro Shibasaki, Marília Caldas, and Nelson Studart
- Subjects
Physics ,Condensed Matter::Materials Science ,Condensed matter physics ,Quantum spin Hall effect ,Condensed Matter::Other ,Quantum point contact ,Quantum oscillations ,Landau quantization ,Quantum Hall effect ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Quantum well ,Spin-½ ,Magnetic field - Abstract
We have investigated transport properties in InAs/AlGaSbAs and InAsSb/AlInSb quantum wells (QW) in the quantum Hall regime. The carrier density in InAs QW is tuned by using a front gate bias, and the contour plot of resistance as a function of perpendicular magnetic field and gate voltage reveals the spin‐resolved subband‐Landau‐level coupling in tilted magnetic fields. An anomalous transport occurred by the coexistence of electrons and holes in the system has been observed both in InAs and InAsSb QWs.
- Published
- 2010
29. Transport Properties of InAs0.1Sb0.9 Thin Films Sandwiched by Al0.1In0.9Sb Layers Grown on GaAs(100) Substrates by Molecular Beam Epitaxy
- Author
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Hirotaka Geka, Atsusi Okamoto, and Ichiro Shibasaki
- Subjects
Electron mobility ,Materials science ,business.industry ,Doping ,Optoelectronics ,Electron ,Thin film ,business ,Layer thickness ,Sheet resistance ,Active layer ,Molecular beam epitaxy - Abstract
Electron mobilities of InSb, InSb/AlInSb and InAsSb/AlInSb grown on GaAs(100) were compared as a function of layer thickness and temperature. InAs0.1Sb0.9 thin active layers sandwiched by Al0.1In0.9Sb layers showed the smallest thickness dependence and very large electron mobility at less than 500nm thickness. Basic transport properties and Sn doping effects of the InAs0.1Sb0.9 were studied.
- Published
- 2008
30. Relationship between transport properties and band diagrams in InAsxSb1−x/Al0.1In0.9Sb quantum wells
- Author
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S. Ishida, Takashi Manago, Hirotaka Geka, and Ichiro Shibasaki
- Subjects
Materials science ,Condensed matter physics ,Band gap ,Fermi level ,General Physics and Astronomy ,Electronic structure ,lcsh:QC1-999 ,symbols.namesake ,Electrical resistivity and conductivity ,Band diagram ,symbols ,Charge carrier ,Electronic band structure ,Quantum well ,lcsh:Physics - Abstract
The resistivity of InAs0.1Sb0.9/Al0.1In0.9Sb quantum wells (QWs) is much lower than that of InSb/Al0.1In0.9Sb QWs, staying low resistivity even at low temperature. Fundamental difference in low temperature transport properties between InSb/Al0.1In0.9Sb and InAs0.1Sb0.9/Al0.1In0.9Sb QWs was revealed, based on the band diagram calculations of these QWs. Band diagrams of InAsxSb1−x/Al0.1In0.9Sb QWs showed that the energy band of the InAsxSb1−x layer moves downward with increasing As content x. The QW is type I at x equal to 0, becomes type II at x equal to 0.1. The Fermi level (EF) of the InSb QWs lies in the band gap and below apart from the bottom of the conduction band, while EF of the InAs0.1Sb0.9 QWs is above the bottom of the conduction band of the well. The calculated sheet carrier densities are in good agreement with the experimental results. It well explains that the sheet carrier density difference between InSb and InAs0.1Sb0.9 QWs mainly originates from this band diagram difference and the position of EF.
- Published
- 2015
31. Interfacial trap states and improvement of low-temperature mobility by doping in InSb/AlInSb quantum wells
- Author
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S. Ishida, Takashi Manago, Hirotaka Geka, and Ichiro Shibasaki
- Subjects
Electron mobility ,Electron density ,Materials science ,Condensed matter physics ,Condensed Matter::Other ,Scattering ,Doping ,General Physics and Astronomy ,Heterojunction ,Ionized impurity scattering ,Condensed Matter::Materials Science ,Electrical resistivity and conductivity ,Condensed Matter::Superconductivity ,Condensed Matter::Strongly Correlated Electrons ,Quantum well - Abstract
The effect of doping on InSb/Al0.1In0.9Sb quantum wells (QWs) was investigated, and it was found that doping improves the electron mobility at low temperatures and leads to a weaker dependence of the resistivity with temperature. The dependence of the carrier density on the well width revealed trap states at the interfaces of the QW whose sheet density per interface was estimated to be about 4 × 1010 cm−2. The low mobility of undoped InSb QWs, in particular, at low temperature seems to have been caused by positively ionized impurity scattering at the interfacial trap states. Doping compensates for the trap states and enhances mobility by suppressing ionized impurity scattering. Thus, intentional doping is necessary for developing high-mobility InSb QW devices. The origin of the trap states is qualitatively discussed.
- Published
- 2015
32. Relationship between transport properties and band diagrams in InAsxSb1-x/Al0.1In0.9Sb quantum wells.
- Author
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Takashi Manago, Shuichi Ishida, Hirotaka Geka, and Ichiro Shibasaki
- Subjects
QUANTUM wells ,QUANTUM dots ,CONDUCTION bands ,ELECTRIC conductivity ,ENERGY bands - Abstract
The resistivity of InAs
0.1 Sb0.9 /Al0.1 In0.9 Sb quantum wells (QWs) is much lower than that of InSb/Al0.1 In0.9 Sb QWs, staying low resistivity even at low temperature. Fundamental difference in low temperature transport properties between InSb/Al0.1 In0.9 Sb and InAs0.1 Sb0.9 /Al0.1 In0.9 Sb QWs was revealed, based on the band diagram calculations of these QWs. Band diagrams of InAsxSb1-x/Al0.1 In0.9 Sb QWs showed that the energy band of the InAsxSb1-x layer moves downward with increasing As content x. The QW is type I at x equal to 0, becomes type II at x equal to0.1 . The Fermi level (EF ) of the InSb QWs lies in the band gap and below apart from the bottom of the conduction band, while EF of the InAs0.1 Sb0.9 QWs is above the bottom of the conduction band of the well. The calculated sheet carrier densities are in good agreement with the experimental results. It well explains that the sheet carrier density difference between InSb and InAs0.1 Sb0.9 QWs mainly originates from this band diagram difference and the position of EF. [ABSTRACT FROM AUTHOR]- Published
- 2015
- Full Text
- View/download PDF
33. Doping Level Dependence of Transport Properties in InAsSb Quantum Wells
- Author
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Hirotaka Geka, Ichiro Shibasaki, Takashi Manago, S. Ishida, Kazumasa Makise, N. Nishizako, and Kazutaka Mitsuishi
- Subjects
Materials science ,Condensed matter physics ,business.industry ,Doping ,General Medicine ,Electron ,Physics and Astronomy(all) ,Low mobility ,Charge-carrier density ,Quntum wells ,Optoelectronics ,InAsSb ,business ,Quantum well ,Sheet resistance - Abstract
We investigated the transport properties of the Al 0.1 In 0.9 Sb/InAs 0.1 Sb 0.9 quantum wells (QWs). Intentional doping of donors to the QW is effective to decrease the sheet resistance and suppress its temperature dependence because the carrier density is maintained to be relatively high in low temperature. Additionally, although there exists a low mobility region near the heterointerface of the QW and a high mobility region far from the interface in this system, the doped electrons contribute to keep high mobility in low temperature because the increase of electrons prevents the accumulation of all electrons in the low mobility region.
- Full Text
- View/download PDF
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