DSpace コミュニティ:http://hdl.handle.net/10098/5402015-03-02T14:56:03Z2015-03-02T14:56:03ZLow-Loss and High-Voltage III-Nitride Transistors for Power Switching ApplicationsKuzuhara, MasaakiTokuda, Hirokunihttp://hdl.handle.net/10098/87222015-02-19T18:00:21Z2015-02-01T00:00:00Zタイトル: Low-Loss and High-Voltage III-Nitride Transistors for Power Switching Applications
著者: Kuzuhara, Masaaki; Tokuda, Hirokuni
抄録: This paper describes recent technological advances on III-nitride-based transistors for power switching applications.
Focuses are placed on the progress toward enhancing the breakdown voltage, lowering the ON -resistance, suppressing current collapse, and reducing the leakage current in AlGaN/GaN
high-electron mobility transistors (HEMTs). Recent publications revealed that the tradeoff relation between ON -resistance and
breakdown voltage in AlGaN/GaN HEMTs exceeded the SiC limit and was getting close to the GaN limit; however, the breakdown voltage achieved was still lower than the theoretical
impact ionization limit. A novel process featuring strain-controlled annealing with a metal stack, including Al gave rise to significant reduction in the sheet resistance in AlGaN/GaN heterostructures, suggesting the possibility of dramatic reduction in ON -resistance of GaN-based power devices. Some of the interesting approaches to suppress current collapse indicated that surface trapping effects must be controlled by the
optimization of surface processing as well as by the reduction of bulk traps in the epitaxial layers. Close correlation between
the local gate leakage current and point defects exposed on the free-standing GaN substrate demonstrated that further reduction
of defects on bulk GaN substrates is truly required as future challenges.2015-02-01T00:00:00ZThick (~1 mm) p-type In x Ga 1–x N(x ~ 0.36) grown by MOVPE at a low temperature (~570 8C)Yamamoto, A.Hasan, T. Md.Kodama, K.Shigekawa, N.Kuzuhara, M.http://hdl.handle.net/10098/87212015-02-19T18:00:19Z2015-02-17T00:00:00Zタイトル: Thick (~1 mm) p-type In x Ga 1–x N(x ~ 0.36) grown by MOVPE at a low temperature (~570 8C)
著者: Yamamoto, A.; Hasan, T. Md.; Kodama, K.; Shigekawa, N.; Kuzuhara, M.
抄録: This paper reports the post-growth annealing effects of low-
temperature grown Mg-doped InGaN. By using MOVPE,
1 mm-thick Mg-doped In x Ga 1–x N (x ~ 0.36) flms are grown at
570 8C. In order to activate the Mg acceptors, grown samples
are treated by the conventional furnace annealing (FA) or the
rapid thermal annealing (RTA). In the case of the FA at 650 8C
for 20 min, the InGaN flm is phase-separated. On the other
hand, the RTA at a temperature higher than 700 8C enables us
to get p-type samples. By using the RTA at 850 for 20 s, p-type
samples with a hole concentration 10 18 –10 19 cm -3 are
successfully obtained without phase separation.2015-02-17T00:00:00ZPower law for frequency-dependence of double layer capacitance of graphene flakesWang, HongxinAoki, Koichi JeremiahChen, JingyuanNishiumi, ToyohikoZeng, XiangdongMa, Xiuyuanhttp://hdl.handle.net/10098/87202015-02-19T18:00:18Z2015-02-01T00:00:00Zタイトル: Power law for frequency-dependence of double layer capacitance of graphene flakes
著者: Wang, Hongxin; Aoki, Koichi Jeremiah; Chen, Jingyuan; Nishiumi, Toyohiko; Zeng, Xiangdong; Ma, Xiuyuan
抄録: The double layer capacitance per weight of graphene (GN) flakes in aqueous solution at the polarized potential increases with a decrease in the ac-frequency, obeying the inverse of the power law of the frequency.
The power law is demonstrated to be equivalent to the constant phase element. The frequency-dependence increases with the thickness of the GN films. Thus, the lower the frequency and the thinner the film is, the larger is the capacitance density per weight. This is confirmed by cyclic voltammetry for several thickness of GN films and several scan rates. Resistance-like voltammograms at thick films are caused by frequencydispersioIEEE TRANSACTIONS ON ELECTRON DEVICESn. The overall capacitive properties of the GN films are as follows: the thickness of one GN flake is estimated to be 2 nm in average from the comparison of the thickness with the capacitances at the HOPG, which is consistent with values by the STM and AFM images.2015-02-01T00:00:00ZAnalytical formula for numerical evaluations of the Wigner rotation matrices at high spinsTajima, Naokihttp://hdl.handle.net/10098/86992015-01-28T18:00:17Z2015-01-01T00:00:00Zタイトル: Analytical formula for numerical evaluations of the Wigner rotation matrices at high spins
著者: Tajima, Naoki
抄録: The Wigner d function, which is the essential part of an irreducible representation of SU(2) and SO(3)
parameterized with Euler angles, has been know to suffer from a serious numerical errors at high spins, if it is
calculated by means of the Wigner formula as a polynomial of cos and sin of half of the second Euler angle. This
paper shows a way to avoid this problem by expressing the d functions as the Fourier series of the half angle. A
precise numerical table of the coefficients of the series is provided as Supplemental Material.2015-01-01T00:00:00Z