Ryoichi Ito

Bio: Ryoichi Ito is an academic researcher from University of Tokyo. The author has contributed to research in topics: Quantum well & Photoluminescence. The author has an hindex of 26, co-authored 172 publications receiving 2436 citations.

Magneto-optical study on excitonic spectra in (C6H13NH3)2PbI4.

Abstract: Magnetoabsorption spectra of the lowest-energy excitons in a layered perovskite-type material (${\mathrm{C}}_{6}$${\mathrm{H}}_{21}$${\mathrm{NH}}_{3}$${)}_{2}$${\mathrm{PbI}}_{4}$ have been measured under pulsed high magnetic fields up to 42 T at 4.2 K in the Faraday configuration (E\ensuremath{\perp}c\ensuremath{\parallel}B) and the Voigt configuration (E\ensuremath{\perp}c\ensuremath{\perp}B). Energy shifts and splittings in the spectra for the Voigt configuration have been observed in this material. For the Faraday configuration, the Zeeman splitting with small diamagnetic shifts has clearly been detected. The diamagnetic coefficients obtained are much smaller than that for ${\mathrm{PbI}}_{2}$, suggesting that the Wannier-exciton model is not a good approximation for the lowest-energy excitons in (${\mathrm{C}}_{6}$${\mathrm{H}}_{13}$${\mathrm{NH}}_{3}$${)}_{2}$${\mathrm{PbI}}_{4}$. Theoretical analysis based on the cationic Frenkel-exciton model yields semiquantitative agreement with the experimental results.

A Nonlinear Optical Organic Crystal for Waveguiding SHG Devices: (−)2-(α-Methylbenzylamino)-5-Nitropyridine (MBANP)

Abstract: A nonlinear optical organic material, (-)2-(α-methylbenzylamino)-5-nitropyridine (MBANP), has been comprehensively investigated with the objective of application to frequency doubling of laser diodes. Its molecular hyperpolarizability is as large as that of p-nitroaniline. MBANP crystallizes with a highly asymmetric molecular arrangement. The largest nonlinear optical coefficient, d22, is measured to be 60 pm/V. The corresponding figure of merit for frequency doubling at 1.064 µm is 3.5 times larger than that for d33 of LiNbO3. Cerenkov-radiation-type, phase-matched second-harmonic generation has been demonstrated utilizing the d22 coefficient by making use of an appropriate waveguiding structure.

Spectral blue shift of photoluminescence in strained‐layer Si1−xGex/Si quantum well structures grown by gas‐source Si molecular beam epitaxy

Abstract: Spectral blue shift of excitonic transition due to quantum confinement in Si0.84Ge0.16/Si strained‐layer quantum wells, grown by gas‐source Si molecular beam epitaxy, is reported. Intense photoluminescence was observed at elevated temperatures though reduced in intensity due to the thermalization of holes to the Si barriers.

Band parameters for III–V compound semiconductors and their alloys

Abstract: We present a comprehensive, up-to-date compilation of band parameters for the technologically important III–V zinc blende and wurtzite compound semiconductors: GaAs, GaSb, GaP, GaN, AlAs, AlSb, AlP, AlN, InAs, InSb, InP, and InN, along with their ternary and quaternary alloys. Based on a review of the existing literature, complete and consistent parameter sets are given for all materials. Emphasizing the quantities required for band structure calculations, we tabulate the direct and indirect energy gaps, spin-orbit, and crystal-field splittings, alloy bowing parameters, effective masses for electrons, heavy, light, and split-off holes, Luttinger parameters, interband momentum matrix elements, and deformation potentials, including temperature and alloy-composition dependences where available. Heterostructure band offsets are also given, on an absolute scale that allows any material to be aligned relative to any other.

GaAs, AlAs, and AlxGa1−xAs: Material parameters for use in research and device applications

Abstract: The Al x Ga1−x As/GaAs heterostructure system is potentially useful material for high‐speed digital, high‐frequency microwave, and electro‐optic device applications Even though the basic Al x Ga1−x As/GaAs heterostructure concepts are understood at this time, some practical device parameters in this system have been hampered by a lack of definite knowledge of many material parameters Recently, Blakemore has presented numerical and graphical information about many of the physical and electronic properties of GaAs [J S Blakemore, J Appl Phys 5 3, R123 (1982)] The purpose of this review is (i) to obtain and clarify all the various material parameters of Al x Ga1−x As alloy from a systematic point of view, and (ii) to present key properties of the material parameters for a variety of research works and device applications A complete set of material parameters are considered in this review for GaAs, AlAs, and Al x Ga1−x As alloys The model used is based on an interpolation scheme and, therefore, necessitates known values of the parameters for the related binaries (GaAs and AlAs) The material parameters and properties considered in the present review can be classified into sixteen groups: (1) lattice constant and crystal density, (2) melting point, (3) thermal expansion coefficient, (4) lattice dynamic properties, (5) lattice thermal properties, (6) electronic‐band structure, (7) external perturbation effects on the band‐gap energy, (8) effective mass, (9) deformation potential, (10) static and high‐frequency dielectric constants, (11) magnetic susceptibility, (12) piezoelectric constant, (13) Frohlich coupling parameter, (14) electron transport properties, (15) optical properties, and (16) photoelastic properties Of particular interest is the deviation of material parameters from linearity with respect to the AlAs mole fraction x Some material parameters, such as lattice constant, crystal density, thermal expansion coefficient, dielectric constant, and elastic constant, obey Vegard’s rule well Other parameters, eg, electronic‐band energy, lattice vibration (phonon) energy, Debye temperature, and impurity ionization energy, exhibit quadratic dependence upon the AlAs mole fraction However, some kinds of the material parameters, eg, lattice thermal conductivity, exhibit very strong nonlinearity with respect to x, which arises from the effects of alloy disorder It is found that the present model provides generally acceptable parameters in good agreement with the existing experimental data A detailed discussion is also given of the acceptability of such interpolated parameters from an aspect of solid‐state physics Key properties of the material parameters for use in research work and a variety of Al x Ga1−x As/GaAs device applications are also discussed in detail

Band parameters for nitrogen-containing semiconductors

Abstract: We present a comprehensive and up-to-date compilation of band parameters for all of the nitrogen-containing III–V semiconductors that have been investigated to date. The two main classes are: (1) “conventional” nitrides (wurtzite and zinc-blende GaN, InN, and AlN, along with their alloys) and (2) “dilute” nitrides (zinc-blende ternaries and quaternaries in which a relatively small fraction of N is added to a host III–V material, e.g., GaAsN and GaInAsN). As in our more general review of III–V semiconductor band parameters [I. Vurgaftman et al., J. Appl. Phys. 89, 5815 (2001)], complete and consistent parameter sets are recommended on the basis of a thorough and critical review of the existing literature. We tabulate the direct and indirect energy gaps, spin-orbit and crystal-field splittings, alloy bowing parameters, electron and hole effective masses, deformation potentials, elastic constants, piezoelectric and spontaneous polarization coefficients, as well as heterostructure band offsets. Temperature an...

External optical feedback effects on semiconductor injection laser properties

Abstract: Influences on the semiconductor laser properties of external optical feedback, i.e., return of a portion of the laser output from a reflector external to the laser cavity, have been examined. Experimental observations with a single mode laser is presented with analysis based on a compound cavity laser model, which has been found to explain essential features of the experimental results. In particular, it has been demonstrated that a laser with external feedback can be multistable and show hysteresis phenomena, analogous to those of non-linear Fabry-Perot resonator. It has also been shown that the dynamic properties of injection lasers are significantly affected by external feedback, depending on interference conditions between returned light and the field inside the laser diode.

Organic–Inorganic Perovskites: Structural Versatility for Functional Materials Design

Abstract: Although known since the late 19th century, organic–inorganic perovskites have recently received extraordinary research community attention because of their unique physical properties, which make them promising candidates for application in photovoltaic (PV) and related optoelectronic devices. This review will explore beyond the current focus on three-dimensional (3-D) lead(II) halide perovskites, to highlight the great chemical flexibility and outstanding potential of the broader class of 3-D and lower dimensional organic-based perovskite family for electronic, optical, and energy-based applications as well as fundamental research. The concept of a multifunctional organic–inorganic hybrid, in which the organic and inorganic structural components provide intentional, unique, and hopefully synergistic features to the compound, represents an important contemporary target.