Since the discovery of graphene, the emerging system of atomically thin materials with a thickness of only a few atomic layers is causing a drastic paradigm-shift in the research fields of material and optical science. The optically generated, bound electron-hole pair (exciton and charged exciton) contributes to the novel optical properties in semiconducting monolayer transition metal dichalcogenides called “beyond graphene”. In this review, we describe our recent studies in novel optical science and applications in atomically thin semiconducting transition metal dichalcogenides.

Recently, SiC power devices have been utilized in various next generation power applications. GaN-HEMTs on silicon are also going to be adopted for new power applications owing to their high-speed switching behavior. On the other hand, GaN bulk wafers have emerged due to the needs of blue LED and laser applications. So far, conventional GaN electron devices utilize 2DEG (two dimensional electron gas) formed on foreign substrates such as silicon, SiC or sapphire. The bulk GaN wafer has the potential to realize high power vertical power devices similar to silicon or SiC. For the realization of GaN vertical devices, there are several key technologies that need to be developed. In this paper, MOS (metal-oxide-semiconductor) technology, as one of the most important key issues to control the transistor characteristics, will be discussed.

The 2016 Nobel Prize in Physics was awarded for the pioneering theoretical work on “topology in materials” that began in the 1980’s. Then, early in this century, by adding relativistic effects (i.e. spin-orbit couplings) as well as expanding the platform from 1D/2D systems to 3D bulk materials, a new “game-changing” paradigm arrived for both the basic and applied sciences of condensed matter physics and materials science. In this article, the materials, properties, and functionality within a novel class of “topological electronic states” (especially 3D topological Insulators and topological superconductors) are reviewed.

The radiation tolerance of triple junction space solar cells has the potential to be improved by embedding InAs quantum dot (QD) layers into the GaAs middle subcell, although the impact of radiation induced defects on devices with QDs is still unclear. Electrically active defects in GaAs p+n diodes with ten embedded layers of InAs QDs are investigated using Deep Level Transient Spectroscopy. Devices are irradiated with high energy protons in order to characterize radiation induced defect levels. Two unique native defect levels are found in a device with QDs, whereas no unique radiation induced defect is observed. The obtained results indicate the radiation tolerance of devices with QDs is expected to be equivalent to a device without QDs.

Silicon carbide (SiC) has received increasing attention as a wide bandgap semiconductor that is promising for high-voltage and low-loss power devices. In this study, impact ionization coefficients in SiC were extracted in the temperature range from room temperature to 150℃, based on photomultiplication experiments for various fabricated pn diodes. By using the impact ionization coefficients obtained in this study, the breakdown voltage of SiC devices and its temperature dependence can be predicted within an error of 2.5%. The breakdown electric field strength of SiC <0001> for non-punch-through structures was also determined as a function of the doping density.

The current status of the study of in vivo molecular delivery systems based on nanosecond pulsed laser-induced photomechanical waves (PMWs) is described. The method for generation of and the characteristics of PMWs and their application to gene delivery and gene therapy, as well as the development for endoscopic application, are reported. We also found that a PMW could enhance the permeability of blood vessels in tissues including the brain, indicating that the blood-brain barrier, which seriously limits molecular delivery to the brain, can be opened by the effect of PMWs. This effect can be applied to selective transvascular molecular delivery.

Imaging mass spectrometry (IMS) is an analytical technique to simultaneously obtain the spatial distributions of multiple atoms and molecules. Molecules such as lipids, proteins, and administered drugs in a biological tissue can comprehensively be observed without labeling. Higher spatial resolution and shorter measuring times compared to conventional scanning IMS are possible with stigmatic IMS, and its present status and future prospects are described. A spatial resolution of 1 μm for an artificial pattern has been shown with a stigmatic IMS device developed by the author and coworkers. Ion images of dyes obtained from a mouse cornea tissue stained with the dyes were matched to its optical photomicrograph. A semiconductor pixel ion detector MALPIX under development for stigmatic IMS is also introduced.

The finite-difference time-domain (FDTD) method and the beam-propagation method (BPM) have widely been used to analyze and design optical waveguide-based devices. In this article, the practical applications of the FDTD method are presented, in which an optical waveguide with high reflection coatings and a band-pass filter using a metal-insulator-metal waveguide are analyzed and discussed. The BPM is also applied to the calculation of eigenmodes with the imaginary-distance procedure. Full-vectorial BPM calculations are given in the application of a polarization rotator with attention to power conservation. Finally, some tips for electromagnetic simulations are also mentioned.