The Experts below are selected from a list of 8103 Experts worldwide ranked by ideXlab platform

Thomas Ihn - One of the best experts on this subject based on the ideXlab platform.

  • tunable valley splitting and Bipolar Operation in graphene quantum dots
    Nano Letters, 2021
    Co-Authors: Chuyao Tong, Rebekka Garreis, Angelika Knothe, Marius Eich, Agnese Sacchi, Kenji Watanabe, Takashi Taniguchi, Vladimir I Falko, Thomas Ihn
    Abstract:

    Quantum states in graphene are 2-fold degenerate in spins, and 2-fold in valleys. Both degrees of freedom can be utilized for qubit preparations. In our bilayer graphene quantum dots, we demonstrate that the valley g-factor gv, defined analogously to the spin g-factor gs for valley splitting in a perpendicular magnetic field, is tunable by over a factor of 4 from 20 to 90, by gate voltage adjustments only. Larger gv results from larger electronic dot sizes, determined from the charging energy. On our versatile device, Bipolar Operation, charging our quantum dot with charge carriers of the same or the opposite polarity as the leads, can be performed. Dots of both polarities are tunable to the first charge carrier, such that the transition from an electron to a hole dot by the action of the plunger gate can be observed. Addition of gates easily extends the system to host tunable double dots.

Vladimir I Falko - One of the best experts on this subject based on the ideXlab platform.

  • tunable valley splitting and Bipolar Operation in graphene quantum dots
    Nano Letters, 2021
    Co-Authors: Chuyao Tong, Rebekka Garreis, Angelika Knothe, Marius Eich, Agnese Sacchi, Kenji Watanabe, Takashi Taniguchi, Vladimir I Falko, Thomas Ihn
    Abstract:

    Quantum states in graphene are 2-fold degenerate in spins, and 2-fold in valleys. Both degrees of freedom can be utilized for qubit preparations. In our bilayer graphene quantum dots, we demonstrate that the valley g-factor gv, defined analogously to the spin g-factor gs for valley splitting in a perpendicular magnetic field, is tunable by over a factor of 4 from 20 to 90, by gate voltage adjustments only. Larger gv results from larger electronic dot sizes, determined from the charging energy. On our versatile device, Bipolar Operation, charging our quantum dot with charge carriers of the same or the opposite polarity as the leads, can be performed. Dots of both polarities are tunable to the first charge carrier, such that the transition from an electron to a hole dot by the action of the plunger gate can be observed. Addition of gates easily extends the system to host tunable double dots.

Chuyao Tong - One of the best experts on this subject based on the ideXlab platform.

  • tunable valley splitting and Bipolar Operation in graphene quantum dots
    Nano Letters, 2021
    Co-Authors: Chuyao Tong, Rebekka Garreis, Angelika Knothe, Marius Eich, Agnese Sacchi, Kenji Watanabe, Takashi Taniguchi, Vladimir I Falko, Thomas Ihn
    Abstract:

    Quantum states in graphene are 2-fold degenerate in spins, and 2-fold in valleys. Both degrees of freedom can be utilized for qubit preparations. In our bilayer graphene quantum dots, we demonstrate that the valley g-factor gv, defined analogously to the spin g-factor gs for valley splitting in a perpendicular magnetic field, is tunable by over a factor of 4 from 20 to 90, by gate voltage adjustments only. Larger gv results from larger electronic dot sizes, determined from the charging energy. On our versatile device, Bipolar Operation, charging our quantum dot with charge carriers of the same or the opposite polarity as the leads, can be performed. Dots of both polarities are tunable to the first charge carrier, such that the transition from an electron to a hole dot by the action of the plunger gate can be observed. Addition of gates easily extends the system to host tunable double dots.

Tsunenobu Kimoto - One of the best experts on this subject based on the ideXlab platform.

  • observation of carrier recombination in single shockley stacking faults and at partial dislocations in 4h sic
    Journal of Applied Physics, 2018
    Co-Authors: Masashi Kato, Shinya Katahira, Yoshihito Ichikawa, Shunta Harada, Tsunenobu Kimoto
    Abstract:

    Because the expansion of single Shockley stacking faults (1SSFs) is an important problem for the viability of SiC Bipolar devices, there is a need to suppress it during device Operation. The expansion mechanism, however, is still unclear. Therefore, the method to suppress the expansion has never been established. An important factor for the expansion could be carrier recombination in 1SSFs because the expansion has only been observed during Bipolar Operation or light illumination. In this study, we characterized carrier recombination by observing the photoluminescence from 1SSFs and partial dislocations (PDs). The luminescence from 1SSFs and PDs showed a fast decay component compared with that from the band edge. This result indicates that the carrier recombination in 1SSFs and at PDs was faster than that in regions without 1SSFs in 4H-SiC. In addition, because of the slower recombination at Si-core PDs compared with that in 1SSFs and at C-core PDs, the velocity of 1SSF expansion would be limited by the carrier recombination at Si-core PDs. The temperature dependence of the decay time implies that the recombination at the Si-core PD was enhanced on increasing the temperature.Because the expansion of single Shockley stacking faults (1SSFs) is an important problem for the viability of SiC Bipolar devices, there is a need to suppress it during device Operation. The expansion mechanism, however, is still unclear. Therefore, the method to suppress the expansion has never been established. An important factor for the expansion could be carrier recombination in 1SSFs because the expansion has only been observed during Bipolar Operation or light illumination. In this study, we characterized carrier recombination by observing the photoluminescence from 1SSFs and partial dislocations (PDs). The luminescence from 1SSFs and PDs showed a fast decay component compared with that from the band edge. This result indicates that the carrier recombination in 1SSFs and at PDs was faster than that in regions without 1SSFs in 4H-SiC. In addition, because of the slower recombination at Si-core PDs compared with that in 1SSFs and at C-core PDs, the velocity of 1SSF expansion would be limited by the c...

  • ultrahigh voltage sic mps diodes with hybrid unipolar Bipolar Operation
    IEEE Transactions on Electron Devices, 2017
    Co-Authors: Hiroki Niwa, Jun Suda, Tsunenobu Kimoto
    Abstract:

    In this paper, ultrahigh-voltage (UHV) SiC devices with hybrid unipolar/Bipolar Operation are introduced and demonstrated. As the first step of such a device, a merged p-i-n Schottky (MPS) diode with an epitaxial p+-anode layer is proposed to reduce the conduction loss of a Bipolar device in the low current region. A “snapback” phenomenon is intensively investigated by analytical modeling, device simulation, and experiment and a design guideline of snapback-free hybrid operating MPS diodes is presented. Using the design guideline, snapback-free MPS diodes are fabricated and forward characteristics are investigated. By using a proper edge termination structure, a UHV SiC MPS diode with breakdown voltage of 11.3 kV is demonstrated.

K M Smedley - One of the best experts on this subject based on the ideXlab platform.

  • one cycle controlled three phase grid connected inverters and their parallel Operation
    IEEE Transactions on Industry Applications, 2008
    Co-Authors: Yang Chen, K M Smedley
    Abstract:

    Grid-connected inverters are necessary for converting the DC power generated by photovoltaic or fuel cells to the AC power of the utility grid. Parallel Operation of these inverters extends the power range to a much higher level and allows modular design. This paper studies current sharing and circulating current among paralleled inverter modules and proposes a new parallel Operation method based on one-cycle control (OCC) with combined vector Operation and Bipolar Operation. With some minor additions to the original OCC circuit and a simple add-on communication path among the individual modules, the current is properly shared among all the inverters and the circulating current is limited to an acceptable range, while OCC advantages such as constant switching frequency, no multipliers, and simple circuitry are preserved. Two OCC inverters of 1.5 kW each were built and tied together using the proposed parallel Operation. Experiments were conducted to demonstrate the simplicity and effectiveness of this method.

  • parallel Operation of one cycle controlled three phase pfc rectifiers
    IEEE Transactions on Industrial Electronics, 2007
    Co-Authors: Yang Chen, K M Smedley
    Abstract:

    Parallel Operation of three-phase power-factor-corrected (PFC) rectifiers is a critical issue for high-power applications, since it extends the power range to a much higher level and allows modular design. The technical challenges are current sharing and circulating current control among the modules. This paper studies these phenomena within two paralleled rectifiers and proposes a new current-sharing method based on one-cycle control (OCC) with vector Operation and Bipolar Operation. With some minor additions to the original OCC circuit and a simple add-on communication path among the individual modules, the input current is shared and the circulating current is limited, while the OCC advantages, such as constant switching frequency, no multipliers, and simple circuitry, are preserved. Two OCC PFC rectifiers of 2.5 kW each were built and tied together using the proposed parallel Operation method. Experiments have demonstrated the simplicity and the effectiveness of this method.

  • parallel Operation of one cycle controlled three phase pfc rectifiers
    Applied Power Electronics Conference, 2005
    Co-Authors: Yang Chen, K M Smedley
    Abstract:

    Parallel Operation of three-phase power factor corrected (PFC) rectifiers extends the power range to a much higher level and allows modular design. However, circulating current among the modules could be a potential problem. This paper studies the circulating current phenomenon within two paralleled rectifiers and proposes a new current sharing method based on one-cycle control with vector Operation and Bipolar Operation. With some minor addition to the original one-cycle control circuit and a simple add-on communication path among the individual modules, the circulating current is eliminated, while the OCC advantages, such as constant switching frequency, no multipliers, and simple circuitry, are preserved. Two one-cycle controlled rectifiers of 2.5 kW each were built and tied together using the proposed parallel Operation method. Experiments have shown the simplicity and the effectiveness of this method.