Masahiro Ikeda

Bio: Masahiro Ikeda is an academic researcher from Keio University. The author has contributed to research in topics: Initial value problem & Mathematics. The author has an hindex of 21, co-authored 143 publications receiving 1763 citations. Previous affiliations of Masahiro Ikeda include Osaka University & Tohoku University.

Site effect on the impurity levels in 4 H , 6 H , and 1 5 R SiC

Abstract: The existence of site-dependent impurity levels caused by inequivalent sites in $4H$, $6H$, and $15R$ SiC has been verified from a study of configuration coordinate phonons. From analyses of donor-acceptor pair and free-to-acceptor luminescence, two kinds of impurity levels of A1, Ga, and B acceptors and N donors substituted cubic-like and hexagonal-like sites are determined. All the impurities in cubic-like sites take deeper levels than those in hexagonal-like sites. Ratios of the ionization energies are approximately constant independent of polytypes and the kind of impurities, 1.0-1.08 for acceptors and 1.55-1.88 for donors, in spite of a wide range of the ionization energies. The origin of the site effect on the impurity level is explained by assuming the existence of a local dielectric constant and a local effective mass. Haynes' rule is found to apply relatively well to N donors in different sites in various polytypes SiC.

Life-span of solutions to semilinear wave equation with time-dependent critical damping for specially localized initial data

Abstract: This paper is concerned with the blowup phenomena for initial value problem of semilinear wave equation with critical time-dependent damping term DW $$\begin{aligned} {\left\{ \begin{array}{ll} \partial _t^2 u(x,t) -\Delta u(x,t) + \dfrac{\mu }{1+t}\partial _t u(x,t)=|u(x,t)|^p, &{} (x,t)\in \mathbb {R}^N \times (0,T),\\ u(x,0)=\varepsilon f(x),&{} x\in \mathbb {R}^N,\\ \partial _t u(x,0)=\varepsilon g(x),&{} x\in \mathbb {R}^N, \end{array}\right. } \end{aligned}$$ where $$N\in \mathbb {N},$$ $$\mu \in [0,\frac{N^2+N+2}{N+2})$$ and $$\varepsilon >0$$ is a parameter describing the smallness of initial data. Given data f, g are compactly supported in a small area inside of the unit ball. The result is the upper bound of lifespan of solution u with respects to the small parameter $$\varepsilon $$ when $$p_F(N)\le p\le p_0(N+\mu ),$$ where $$p_F(N)$$ denotes the Fujita exponent for the nonlinear heat equations and $$p_0(n)$$ denotes the Strauss exponent for nonlinear wave equation (DW) in n-dimension with $$\mu =0.$$ Consequently, by connecting the result of D’Abbicco–Lucente–Reissig (J Differ Equ 259:5040–5073, 2015), our result clarifies the threshold exponent $$p_0(N+\mu )$$ for dividing blowup phenomena and global existence of small solutions when $$N=3.$$ The crucial idea is to construct suitable test functions satisfying the conjugate linear equation $$\partial _t^2\Phi -\Delta \Phi -\partial _t(\frac{\mu }{1+t}\Phi )=0$$ of (DW) including the Gauss hypergeometric functions; note that the construction of test functions is different from Zhou–Han (Commun Partial Differ Equ 39:439–451, 2014).

Repeated temperature modulation epitaxy for p-type doping and light-emitting diode based on ZnO

Abstract: Since the successful demonstration of a blue light-emitting diode (LED)1, potential materials for making short-wavelength LEDs and diode lasers have been attracting increasing interest as the demands for display, illumination and information storage grow2,3,4. Zinc oxide has substantial advantages including large exciton binding energy, as demonstrated by efficient excitonic lasing on optical excitation5,6. Several groups have postulated the use of p-type ZnO doped with nitrogen, arsenic or phosphorus7,8,9,10, and even p–n junctions11,12,13. However, the choice of dopant and growth technique remains controversial and the reliability of p-type ZnO is still under debate14. If ZnO is ever to produce long-lasting and robust devices, the quality of epitaxial layers has to be improved as has been the protocol in other compound semiconductors15. Here we report high-quality undoped films with electron mobility exceeding that in the bulk. We have used a new technique to fabricate p-type ZnO reproducibly. Violet electroluminescence from homostructural p–i–n junctions is demonstrated at room-temperature.

Luminescence properties of defects in GaN

Abstract: Gallium nitride (GaN) and its allied binaries InN and AIN as well as their ternary compounds have gained an unprecedented attention due to their wide-ranging applications encompassing green, blue, violet, and ultraviolet (UV) emitters and detectors (in photon ranges inaccessible by other semiconductors) and high-power amplifiers. However, even the best of the three binaries, GaN, contains many structural and point defects caused to a large extent by lattice and stacking mismatch with substrates. These defects notably affect the electrical and optical properties of the host material and can seriously degrade the performance and reliability of devices made based on these nitride semiconductors. Even though GaN broke the long-standing paradigm that high density of dislocations precludes acceptable device performance, point defects have taken the center stage as they exacerbate efforts to increase the efficiency of emitters, increase laser operation lifetime, and lead to anomalies in electronic devices. The p...

Methods Of Modern Mathematical Physics

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