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Hokkaido University Collection of Scholarly and Academic Papers (135.711 recursos)

HUSCAP (Hokkaido University Collection of Scholarly and Academic Papers) contains peer-reviewed journal articles, proceedings, educational resources and any kind of scholarly works of Hokkaido University.

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Mostrando recursos 1 - 20 de 62

  1. Origin of positive fixed charge at insulator/AlGaN interfaces and its control by AlGaN composition

    Matys, M.; Stoklas, R.; Blaho, M.; Adamowicz, B.
    The key feature for the precise tuning of V-th in GaN-based metal-insulator-semiconductor (MIS) high electron mobility transistors is the control of the positive fixed charge (Q(f)) at the insulator/III-N interfaces, whose amount is often comparable to the negative surface polarization charge (Q(pol)(-)). In order to clarify the origin of Q(f), we carried out a comprehensive capacitance-voltage (C-V) characterization of SiO2/AlxGa1-xN/GaN and SiN/AlxGa1-xN/GaN structures with Al composition (x) varying from 0.15 to 0.4. For both types of structures, we observed a significant V-th shift in C-V curves towards the positive gate voltage with increasing x. On the contrary, the Schottky gate...

  2. Detection of charge dynamics of a tetraphenylporphyrin particle using GaAs-based nanowire enhanced by particle-metal tip capacitive coupling

    Okamoto, Shoma; Sato, Masaki; Sasaki, Kentaro; Kasai, Seiya
    We investigate a detection technique of charge dynamics of a molecular particle using a GaAs-based nanowire where the charge sensitivity is locally enhanced by particle-metal tip capacitive coupling. By equivalent circuit analysis, it was clarified that the nanowire channel potential becomes sensitive to the molecular particle on the nanowire when the particle is capacitively coupled with a metal tip. The concept was demonstrated using a GaAs-based nanowire with tetraphenylporphyrin (TPP) particles on its surface and a measurement system integrating an atomic force microscope (AFM) and a dynamic current measurement monitor/spectrum analyzer. When the metal tip was in contact with a...

  3. Precise thickness control in recess etching of AlGaN/GaN hetero-structure using photocarrier-regulated electrochemical process

    Kumazaki, Yusuke; Uemura, Keisuke; Sato, Taketomo; Hashizume, Tamotsu
    The photocarrier-regulated electrochemical (PREC) process was developed for fabricating recessed-gate AlGaN/GaN high-electron-mobility transistors (HEMTs) for normally off operation. The PREC process is based on photo-assisted electrochemical etching using low-energy chemical reactions. The fundamental photo-electrochemical measurements on AlGaN/GaN heterostructures revealed that the photo-carriers generated in the top AlGaN layer caused homogeneous etching of AlGaN with a smooth surface, but those generated in the GaN layer underneath caused inhomogeneous etching that roughens the surface. The concept of the PREC process is to supply the photo-carriers generated only in the AlGaN layer by selecting proper conditions on light wavelength and voltage. The phenomenon...

  4. Implementation of a noise-coexistence threshold logic architecture on a GaAs-based nanowire FET network

    Kuroda, Ryota; Kasai, Seiya
    Toward reconfigurable and noise-coexistence information processing system utilizing nanostructures, we study a threshold logic circuit and a double threshold function using a GaAs-based nanowire field-effect transistor (FET) network. A noise coexistence capability is based on a noise-assisted state transition in a threshold function in a threshold logic element. We fabricate a circuit reconfigurable between NAND and NOR functions. A hysteresis transfer characteristic with double threshold is realized in the GaAs nanowire by using a silicon nitride (SiN) as the gate insulator. We introduce a unique inverter design using the SiN-gate FET as a load to achieve the transfer characteristic with...

  5. Detection of deep-level defects and reduced carrier concentration in Mg-ion-implanted GaN before high-temperature annealing

    Akazawa, Masamichi; Yokota, Naoshige; Uetake, Kei
    We report experimental results for the detection of deep-level defects in GaN after Mg ion implantation before high-temperature annealing. The n-type GaN samples were grown on GaN free-standing substrates by metalorganic vapor phase epitaxy. Mg ions were implanted at 50 keV with a small dosage of 1.5 x 10(11) cm(-2), which did not change the conduction type of the n-GaN. By depositing Al2O3 and a Ni/Au electrode onto the implanted n-GaN, metal-oxide-semiconductor (MOS) diodes were fabricated and tested. The measured capacitance-voltage (C-V) characteristics showed a particular behavior with a plateau region and a region with an anomalously steep slope. Fitting...

  6. State of the art on gate insulation and surface passivation for GaN-based power HEMTs

    Hashizume, Tamotsu; Nishiguchi, Kenya; Kaneki, Shota; Kuzmik, Jan; Yatabe, Zenji
    In this article, we review recent progress on AlGaN/GaN and InAlN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) using Al-based oxides, nitride dielectrics, SiO2 and high-k dielectrics. Although GaN MIS-HEMTs have been suffering from the instability of threshold voltage (V-TH), recent interface technologies using in-situ SiNx and surface oxidation of (Al)GaN achieved excellent DC and dynamic performances of GaN MIS-HEMTs with stable V-TH. Furthermore, a new design of the gate dielectric such as a nanolaminate structure has been applied to GaN HEMTs. GaN-based MIS-HEMTs sometimes showed sudden current saturation at forward gate bias, and we discuss effects of electronic states at insulator-semiconductor interfaces...

  7. Mechanism of yellow luminescence in GaN at room temperature

    Matys, M.; Adamowicz, B.
    We investigated the excitation intensity (U) dependent photoluminescence (PL), at room temperature (RT), from GaN-based metal-insulator-semiconductor structures under gate bias (VG) fromaccumulation to deep depletion resulting in variations of the space charge region width. We found that depending on VG, different U-dependencies of the YL band energy position (blueshift or redshift), shape (band enlargement or narrowing) and intensity (signal saturation) can be obtained. In order to explain such an unusual YL behavior, we developed a phenomenological PL model, which is based on the solution of the three-dimensional Poisson's equation, current continuity equations and rate equations, and which takes into account...

  8. On the origin of interface states at oxide/III-nitride heterojunction interfaces

    Matys, M.; Adamowicz, B.; Domanowska, A.; Michalewicz, A.; Stoklas, R.; Akazawa, M.; Yatabe, Z.; Hashizume, T.
    The energy spectrum of interface state density, D-it(E), was determined at oxide/III-N heterojunction interfaces in the entire band gap, using two complementary photo-electric methods: (i) photo-assisted capacitance-voltage technique for the states distributed near the midgap and the conduction band (CB) and (ii) light intensity dependent photo-capacitance method for the states close to the valence band (VB). In addition, the Auger electron spectroscopy profiling was applied for the characterization of chemical composition of the interface region with the emphasis on carbon impurities, which can be responsible for the interface state creation. The studies were performed for the AlGaN/GaN metal-insulator-semiconductor heterostructures (MISH)...

  9. On the origin of interface states at oxide/III-nitride heterojunction interfaces

    Matys, M.; Adamowicz, B.; Domanowska, A.; Michalewicz, A.; Stoklas, R.; Akazawa, M.; Yatabe, Z.; Hashizume, T.
    The energy spectrum of interface state density, D-it(E), was determined at oxide/III-N heterojunction interfaces in the entire band gap, using two complementary photo-electric methods: (i) photo-assisted capacitance-voltage technique for the states distributed near the midgap and the conduction band (CB) and (ii) light intensity dependent photo-capacitance method for the states close to the valence band (VB). In addition, the Auger electron spectroscopy profiling was applied for the characterization of chemical composition of the interface region with the emphasis on carbon impurities, which can be responsible for the interface state creation. The studies were performed for the AlGaN/GaN metal-insulator-semiconductor heterostructures (MISH)...

  10. Highly-stable and low-state-density Al2O3/GaN interfaces using epitaxial n-GaN layers grown on free-standing GaN substrates

    Kaneki, Shota; Ohira, Joji; Toiya, Shota; Yatabe, Zenji; Asubar, Joel T.; Hashizume, Tamotsu
    Interface characterization was carried out on Al2O3/GaN structures using epitaxial n-GaN layers grown on free-standing GaN substrates with relatively low dislocation density (<3 x 10(6) cm(-2)). The Al2O3 layer was prepared by atomic layer deposition. The as-deposited metal-oxide-semiconductor (MOS) sample showed a significant frequency dispersion and a bump-like feature in capacitance-voltage (C-V) curves at reverse bias, showing high-density interface states in the range of 10(12) cm(-1) eV(-1). On the other hand, excellent C-V characteristics with negligible frequency dispersion were observed from the MOS sample after annealing under a reverse bias at 300 degrees C in air for 3 h. The...

  11. Highly-stable and low-state-density Al2O3/GaN interfaces using epitaxial n-GaN layers grown on free-standing GaN substrates

    Kaneki, Shota; Ohira, Joji; Toiya, Shota; Yatabe, Zenji; Asubar, Joel T.; Hashizume, Tamotsu
    Interface characterization was carried out on Al2O3/GaN structures using epitaxial n-GaN layers grown on free-standing GaN substrates with relatively low dislocation density (<3 x 10(6) cm(-2)). The Al2O3 layer was prepared by atomic layer deposition. The as-deposited metal-oxide-semiconductor (MOS) sample showed a significant frequency dispersion and a bump-like feature in capacitance-voltage (C-V) curves at reverse bias, showing high-density interface states in the range of 10(12) cm(-1) eV(-1). On the other hand, excellent C-V characteristics with negligible frequency dispersion were observed from the MOS sample after annealing under a reverse bias at 300 degrees C in air for 3 h. The...

  12. Insulated gate and surface passivation structures for GaN-based power transistors

    Yatabe, Zenji; Asubar, Joel T; Hashizume, Tamotsu
    Recent years have witnessed GaN-based devices delivering their promise of unprecedented power and frequency levels and demonstrating their capability as an able replacement for Si-based devices. High-electron-mobility transistors (HEMTs), a key representative architecture of GaN-based devices, are well-suited for high-power and high frequency device applications, owing to highly desirable III-nitride physical properties. However, these devices are still hounded by issues not previously encountered in their more established Si- and GaAs-based devices counterparts. Metal–insulator–semiconductor (MIS) structures are usually employed with varying degrees of success in sidestepping the major problematic issues such as excessive leakage current and current instability. While different insulator...

  13. Current linearity and operation stability in Al2O3-gate AlGaN/GaN MOS high electron mobility transistors

    Nishiguchi, Kenya; Kaneki, Syota; Ozaki, Shiro; Hashizume, Tamotsu
    To investigate current linearity and operation stability of metal-oxide-semiconductor (MOS) AlGaN/GaN high electron mobility transistors (HEMTs), we have fabricated and characterized the Al2O3-gate MOS-HEMTs without and with a bias annealing in air at 300 degrees C. Compared with the as-fabricated (unannealed) MOS HEMTs, the bias-annealed devices showed improved linearity of I-D-V-G curves even in the forward bias regime, resulting in increased maximum drain current. Lower subthreshold slope was also observed after bias annealing. From the precise capacitance-voltage analysis on a MOS diode fabricated on the AlGaN/GaN heterostructure, it was found that the bias annealing effectively reduced the state density at...

  14. Current linearity and operation stability in Al2O3-gate AlGaN/GaN MOS high electron mobility transistors

    Nishiguchi, Kenya; Kaneki, Syota; Ozaki, Shiro; Hashizume, Tamotsu
    To investigate current linearity and operation stability of metal-oxide-semiconductor (MOS) AlGaN/GaN high electron mobility transistors (HEMTs), we have fabricated and characterized the Al2O3-gate MOS-HEMTs without and with a bias annealing in air at 300 degrees C. Compared with the as-fabricated (unannealed) MOS HEMTs, the bias-annealed devices showed improved linearity of I-D-V-G curves even in the forward bias regime, resulting in increased maximum drain current. Lower subthreshold slope was also observed after bias annealing. From the precise capacitance-voltage analysis on a MOS diode fabricated on the AlGaN/GaN heterostructure, it was found that the bias annealing effectively reduced the state density at...

  15. Robust myoelectric signal detection based on stochastic resonance using multiple-surface-electrode array made of carbon nanotube composite paper

    Shirata, Kento; Inden, Yuki; Kasai, Seiya; Oya, Takahide; Hagiwara, Yosuke; Kaeriyama, Shunichi; Nakamura, Hideyuki
    We investigated the robust detection of surface electromyogram (EMG) signals based on the stochastic resonance (SR) phenomenon, in which the response to weak signals is optimized by adding noise, combined with multiple surface electrodes. Flexible carbon nanotube composite paper (CNT-cp) was applied to the surface electrode, which showed good performance that is comparable to that of conventional Ag/AgCl electrodes. The SR-based EMG signal system integrating an 8-Schmitt-trigger network and the multiple-CNT-cp-electrode array successfully detected weak EMG signals even when the subject's body is in the motion, which was difficult to achieve using the conventional technique. The feasibility of the SR-based...

  16. Detection of discrete surface charge dynamics in GaAs-based nanowire through metal-tip-induced current fluctuation

    Sato, Masaki; Yin, Xiang; Kuroda, Ryota; Kasai, Seiya
    We investigated the detection of discrete charge dynamics of an electron trap in a GaAs-based nanowire surface through current fluctuation induced by a metallic scanning probe tip. An equivalent circuit model indicated that the charge state in the surface strongly reflects the channel potential when the local surface potential is fixed by the metal tip, which suggests that random charging and discharging dynamics of the trap appears as random telegraph signal (RTS) noise in the nanowire current. Experimental demonstration of the concept was carried out using a GaAs-based nanowire and an atomic force microscope (AFM) system with a conductive tip....

  17. Detection of molecular charge dynamics through current noise in a GaAs-based nanowire FET

    Inoue, Shinya; Kuroda, Ryota; Yin, Xiang; Sato, Masaki; Kasai, Seiya
    The detection of static and dynamic molecular charge states using a GaAs-based nanowire field-effect transistor (FET) was investigated. Tetraphenylporphyrin (TPP) was put on the device as target molecules. After coating TPP on the FET, the drain current clearly decreased. On the other hand, the current largely increased by 405-nm light irradiation, indicating that TPP worked as a photo-excited donor. The light irradiation on the FET also induced a Lorentzian noise component, which was superimposed onto conventional 1/f noise. These behaviors were not seen in the gateless nanowire even with TPP. The obtained results indicated that electrical interaction between TPP and...

  18. Structural parameter dependence of directed current generation in GaAs nanowire-based electron Brownian ratchet devices

    Abe, Yushi; Kuroda, Ryota; Ying, Xiang; Sato, Masaki; Tanaka, Takayuki; Kasai, Seiya
    We investigated the structural parameter dependence of the directed current in GaAs-nanowire-based Brownian ratchet devices. The directed current was generated by flashing a ratchet potential array repeatedly using multiple asymmetric gates with a periodic signal. The amount of current in the fabricated device increased as the nanowire width W decreased, which contradicted the theoretical model. The current also depended on the number of the gates N, when N was smaller than 6. We discussed the obtained results in terms of the structural parameter dependence of carrier transfer efficiency and the effect of electron reservoirs on current generation in flashing ratchet...

  19. Characterization of GaAs-Based Three-Branch Nanowire Junction Devices by Light-Induced Local Conductance Modulation Method

    Sato, Masaki; Kasai, Seiya
    Nonlinear voltage transfer characteristics in GaAs-based three-branch nanowire junction (TBJ) devices were investigated by a light-induced local conductance modulation method. In this measurement system, the conductance in the device was locally increased by focused laser light irradiation. The nonlinear transfer curve was greatly changed when the laser light was irradiated on the positively biased branch. The conductance domain was found to exist at the end of the positively biased branch of the TBJ by scanning the light position. When a SiNx thin layer was deposited on the nanowire surface, the surface potential was increased and the nonlinearity in the transfer...

  20. GaAs-Based Nanowire Devices with Multiple Asymmetric Gates for Electrical Brownian Ratchets

    Tanaka, Takayuki; Nakano, Yuki; Kasai, Seiya
    GaAs-based nanowire devices having multiple asymmetric gates for electrical Brownian ratchets were fabricated and characterized. From three-dimensional potential simulation results and current–voltage characteristics, we confirmed the formation of the asymmetric potential in our device design. Direct current was generated at room temperature by repeatedly switching the potential in a multiple-asymmetric-gate device on and off. Such current was not observed in either a single-asymmetric-gate device or a multiple-symmetric-gate device. The current direction and input frequency dependences of the net current indicated that the observed current was generated by the flashing-ratchet mechanism.

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