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The p-Al0.35Ga0.65As/n-InGaP heterojunction solar cells are promising competitors compared with conventional InGaP or AlGaAs solar cells as the heterogeneous combination can overcome the demerits of each material. However, InGaP has an optimized growth temperature much lower than that of AlGaAs in metal-organic vapor phase epitaxy (MOVPE) growth. Therefore, a challenge arises from oxygen contamination at the hetero-interface during temperature adjustment for obtaining MOVPE-grown high-quality p-AlGaAs/n-InGaP heterojunction. Here we report that a temperature-graded layer (TGL) of AlGaAs can solve the issue of growth temperature mismatch, and significantly improve the voltage performance of AlGaAs/InGaP solar cells. Absolute electroluminescence (EL) measurement and atomic force microscopy (AFM) confirmed a smooth interface with less non-radiative recombination after TGL was applied. The temperature-graded growth is verified able to improve the AlGaAs/InGaP interface quality and provides a scalable method for AlGaAs-based heterogeneous growth.

A transparent, optically observable microfluidic device for microwave-induced chemical reactions using 24.125 GHz ISM band incorporating was developed. The microfluidic channels can pass through gaps in the post-wall waveguide. The post-wall waveguide allows microwave irradiation to be applied to designed area of the microfluidic channel. In this study, Polydimethylsiloxane (PDMS), commonly used in microfluidic devices, was used as the microwave waveguide material. A glass plate sputtered with indium tin oxide was used to shield microwave leakage to the top and bottom. 4 W of microwave input power was used to heat ethylene glycol, which is used as a solvent in chemical synthesis, in the channels of the fabricated device, and a temperature rise to 100 °C was observed in 70 s. We believe that the use of PDMS as a waveguide material will facilitate observation during microwave irradiation using optics and combination with other microreactors.

In this study, Sc concentration dependence of Sc x Al1−x N/AlN/poly-crystalline diamond/Si surface acoustic wave (SAW) characteristics at high Sc from 23.8% to 44.3% was investigated by fabricating one-port SAW resonator at high frequency. 3.8 GHz one-port resonator fabricated on Sc0.43Al0.57N showed an excellent performance of electro-mechanical coupling coefficient (K 2) as high as 6.34% for 2nd mode Sezawa wave, which enables a wide bandwidth in high frequency applications. The temperature coefficient of frequency was approximately −40 to −50 ppm deg−1 for the device fabricated with Sc concentration of 42.9%. This is a smaller value compared to conventional high K2 bulk materials such as LiNbO3. As the result, a high K2 6.34% material system at a higher Sc concentration of ScAlN/AlN/PCD was found to be possible at a high phase velocity of 7000 m s−1. Combined with the extremely high-power durability of diamond based device, high-power durable wideband SAW device at high frequency can be expected.

An optical unitary processor (OUP) is a programmable photonic circuit to achieve arbitrary unitary operation for various applications, including optical communication, deep learning, and quantum computing. Conventionally, OUPs are implemented by cascading 2 × 2 reconfigurable interferometers, but this scheme cannot easily be extended to multiple wavelength and polarization channels due to the strict requirement to employ 50:50 beam splitters. Here, we demonstrate that an OUP using multiport directional couplers (DCs) can realize independent unitary conversion of multiple wavelength and polarization channels simultaneously. This OUP is based on the multi-plane light conversion (MPLC) principle, which does not require a specific transformation at each layer, unlike the conventional scheme. Thanks to this unique robustness of the MPLC method and strong wavelength/polarization dependence of multiport DCs, we numerically show that independent unitary transformations can be applied to up to 16 channels (2 polarization × 4 wavelengths) using a single device.

We developed implementation technologies for artificial vision devices compatible with suprachoroidal transretinal stimulation. We aimed to develop a device that can be safely implanted in the sclera of the eye for a long period. Using parylene C and bioceramics as biocompatible base materials, we realized a device with high in vivo safety by making the device structure flexible and reducing the wires of control signals. We successfully created a prototype device that combines a flexible wire structure based on a parylene C thin film with a wire-saving CMOS smart electrode structure based on CMOS integrated circuits. We conducted in vitro and in vivo experiments to confirm their performances. The immersion test confirmed that the device could work normally for four days. Furthermore, in the in vivo experiments using rats, we successfully measured evoked potentials in the brain induced by the stimulation current using the device.

We present the boron nitride (BN) phase diagram at 3–6 GPa and 1100 °C–2200 °C using a modified belt-type high-pressure apparatus. The cubic BN (cBN)–hexagonal BN (hBN) phase boundary was determined using the hBN–Mg3BN3 catalyst system as a starting material at 4–5.5 GPa. Additional experiments were conducted at 3–4 and 4–6 GPa using cBN powder or hBN–Ca3B2N4 catalyst as a starting material. In the hBN–catalyst system, the rate of cBN nucleation was reduced by the growth of metastable hBN crystals under the cBN-stable pressure–temperature conditions. The stable BN phases were identified from the samples reacted with a longer run duration. The phase boundary line between hBN and cBN was determined as the equation P (GPa) = T (°C)/400 + 0.3, which agreed with the boundary lines calculated by Gruber and Grüneis and by Nikaido et al.

Sputtering-made magnetic thin films with metal–ceramic multilayer structures have been reported to achieve excellent magnetic properties and/or new functions for various magnetic materials. However, sputtering-made magnetic films tend to have 10 or fewer layers because the main applications of thin films, such as magnetic sensors, recording heads and recording media, require thin films thinner than 1 μm. This paper reports an Fe–Co/glass multilayer thick-film that has an approximate thickness of 10 μm (above 100 layers). This thick-film was prepared via pulsed laser deposition using several composite targets (two- or three-layer targets) consisting of an Fe–Co alloy (or Fe–Co sheet) and a glass plate. The fabrication of an Fe–Co single-layer film and a glass single-layer film was examined to determine the optimal defocus rate for the composite target. Then, we confirmed that the use of a [glass plate]/[Fe–Co alloy] two-layer target enabled the local formation of a [20 nm thick Fe–Co]/[10 nm thick glass) laminated structure with approximately 130 layers. An Fe–Co/glass multilayer structure was formed by using a three-layer target of a [Fe–Co sheet]/[glass plate]/[metal alloy]. Nonetheless, the results also suggest that large glass droplets should be removed in future work to create homogeneous multilayer thick-films.

A GaN crystal comprises two polar structures along the c-axis direction, and functions as a quasi-phase-matching (QPM) crystal by fabricating a periodic inversion structure. We fabricated GaN-QPM crystals to design rib-waveguide-type devices for achieving highly efficient wavelength conversion. The QPM period required for wavelength conversion was calculated in the design phase of the device structure. GaN-QPM crystals with the obtained period were fabricated using double-polarity selective-area growth (DP-SAG). The GaN-QPM crystal was then used to fabricate a second-harmonic generation (SHG) device with a rib waveguide structure. Optical measurements revealed that the device achieved wavelength conversion from 840 to 420 nm. Further, the SHG device exhibited a wavelength conversion efficiency of 1.5 × 10–4% W−1. These results indicated that GaN-QPM crystals fabricated by DP-SAG can be used for wavelength conversion.

From ∼1500 published journal papers on organic photovoltaics (OPVs), we extracted the OPV performance parameters of power conversion efficiency (PCE), open-circuit voltage (V OC) and short-circuit current density (J SC) and the chemical structures of photovoltaic layer materials to investigate the relation between the extracted data of OPVs accompanied by non-fullerene acceptors (NFAs). Our analysis indicates that there is a suitable range of V OC for high PCE or J SC in NFAs. We also investigated the correlation between the performance parameters and chemical structures of small-molecule NFAs. Our approach may enable us to provide a new design strategy for high-performance OPVs.

The phase transformation of overgrown CaSi crystal on an (00l)-oriented epitaxial CaSi2 film was studied using high-angle annular dark-field scanning transmission electron microscopy. After annealing at 450 °C under vacuum conditions, the CaSi domain transformed to the CaSi2 phase with thin Si layers. The transformed CaSi2 crystal formed epitaxially along the under-layer epitaxial CaSi2 film. The results suggest that Ca atoms in the overgrown CaSi domain diffused to the outermost passivated silicon oxide layer during the low-temperature vacuum anneal.

β-Ga2O3 has a high potential for power device applications because of a high Baliga’s figure and the availability of large-scale wafers. However, the piezoresistive effect of β-Ga2O3 has not been investigated in detail, and its piezoresistive coefficient has not been reported. This study evaluates the piezoresistive coefficient of β-Ga2O3 in the direction using a mechanical stress simulator and a device simulator, which includes our piezoresistive effect model. In this study, the piezoresistive effect model and simulation method are applied to β-Ga2O3 for the first time. The piezoresistor model of β-Ga2O3 is simulated to evaluate the piezoresistive coefficient of β-Ga2O3. The experimentally obtained gauge factor with and without the contact effect is −5.8 and −3.6, respectively. The piezoresistive coefficient with and without the contact effect is −2.0 × 10−11 Pa−1 and −1.2 × 10−11 Pa−1, respectively. The piezoresistive coefficient is used to evaluate the piezoresistive effect at 1000 °C through thermal analysis.

A novel characterization method for the nitrogen doping concentration in heavily nitrogen-doped (more than 1 × 1019 cm−3) 4H-SiC crystals using Raman scattering microscopy is proposed. The method utilizes the integrated intensity of the longitudinal optical phonon-plasmon coupled (LOPC) mode signal arising at 1100 cm−1, which exhibits marked changes in the peak position, intensity, and line shape when the nitrogen concentration in 4H-SiC crystals changes. The proposed method showed a much higher sensitivity to the nitrogen doping variation in 4H-SiC crystals compared to the conventional characterization methods using the LOPC peak shift and the Fano interference, and detected a small variation (~1%) in the nitrogen doping concentration across the (000) facet of heavily nitrogen-doped 4H-SiC crystals.

A novel remote dry processing of specific reactive negative ions with a deflection and focusing system is being developed to precisely control their energy, flux and reaching position on the nanoscale. The trajectory simulations of the negative ion extraction and transport for the design of this processing apparatus have been carried out using SIMION software. It is found from the simulation results that the ion beams with good focusing characteristics, high directivity and appropriate current amount can be successfully extracted from the plasma source and transported to the reactor chamber through the deflection and focusing system. The simulation results of O− ion beam exhibit that the extraction and transport characteristics of the flat intermediate electrode are superior to those of the oblique one.

A silicon wafer etching using a burst pulse high-power inductively coupled plasma (ICP) is investigated. A 200 μs wide burst of a 157 kHz power supply is employed to generate ICP with a repetition rate of 50 Hz. A rectangular pulsed voltage synchronized with the burst power supply is applied upto 1 kV at the wafer. Mixed gas of argon (Ar) and tetrafluoromethane (CF4) is supplied into the vacuum chamber. The plasma density and electron temperature are 1019 m−3 and 2.8 eV where the wafer is, respectively. In the case of Ar plasma, the silicon etching rate is 0.01 μm min−1 with 1000 V negative bias. The etching rate increases to 0.23 μm min−1 by adding CF4 into Ar and increases linearly with increasing the bias voltage. The target current and emission intensity of Ar+ and F* are depended on bias voltage from −300 to −1000 V. The etching rate sharply increases by increasing CF4 content from 0% to 10%, and it becomes almost constant at 10%. The dependency of emission intensity of F* on CF4 content is similar to the dependency the etching rate.