The 50 most-cited articles in Japanese Journal of Applied Physics, 2018

Abstract Underwater wireless optical communication (UWOC) is a wireless communication technology that uses visible light to transmit data in underwater environment. Compared to radio-frequency (RF) and acoustic underwater techniques, UWOC has many advantages including large information bandwidth, unlicensed spectrum and low power requirements. This review paper provides an overview of the latest UWOC research. Additionally, we present a detailed description of transmitter and receiver technologies which are key components of UWOC systems. Moreover, studies investigating underwater optical channel models for both simple attenuation and the impact of turbulence including air bubbles and inhomogeneous salinity and temperature are also described. Future research challenges are identified and outlined.

Abstract High-efficiency back-contact heterojunction crystalline Si (c-Si) solar cells with record-breaking conversion efficiencies of 26.7% for cells and 24.5% for modules are reported. The importance of thin-film Si solar cell technology for heterojunction c-Si solar cells with amorphous Si passivation layers in improving conversion efficiency and reducing production cost is demonstrated. Our attempts to reduce the production cost of a heterojunction c-Si solar cell by applying a SiO x layer prepared by a plasma-enhanced CVD method are presented. The characteristics of heterojunction c-Si solar cells are clarified by comparing them with those of practical homojunction solar cells, and crucial targets for industrialization of back-contact heterojunction c-Si solar cells are discussed. Owing to the recent improvement of c-Si solar cells and perovskite solar cells, conversion efficiencies over 30% have become a realistic target by using a two-terminal tandem structure with a heterojunction c-Si solar cell and a perovskite solar cell.

Abstract Phonon engineering is expected to contribute to further development of various fields and technologies such as electronics, photonics, thermal engineering, and materials science. Although phonons inherently exist in condensed matter, their behavior strongly depends on the scale of the system and the materials, and they play a major role in electrical, optical, thermal, and mechanical properties. Therefore, researchers have been attempting to find effective ways to control phonons to modify the material properties — in this regard, nanostructuring was found to be highly effective. Here, we review recent advances in the simulations and experiments on phonon transport and thermal conduction control in nanostructures. We mainly focus on tailored nanostructures, especially phononic crystals of which the design is based on the nanoscale phonon transport property.

Abstract Forty years has passed since I conceived the idea of a vertical-cavity surface-emitting laser (VCSEL) in 1977. This review is focused on its research and development by featuring host technologies that contributed to the realization of usable devices. After numerous innovations, the VCSEL is now generating new applications such as high-speed local area networks, computer mice, parallel optical interconnects, laser printers, face recognition systems, and various optical sensors.

Abstract A high breakdown voltage of 5.0 kV has been achieved for the first time in vertical GaN p–n junction diodes by using our newly developed guard-ring structures. A resistance device was inserted between the main diode portion and the guard-ring portion in a ring-shaped p–n diode to generate a voltage drop over the resistance device by leakage current flowing through the guard-ring portion under negatively biased conditions before breakdown. The voltage at the outer mesa edge of the guard-ring portion, where the electric field intensity is highest and the destructive breakdown usually occurs, is decreased by the voltage drop, so the electric field concentration in the portion is reduced. By adopting this structure, the breakdown voltage ( V B ) is raised by about 200 V. Combined with a low measured on-resistance ( R on ) of 1.25 mΩ cm 2 , Baliga’s figure of merit was as high as 20 GW/cm 2 .

In this review, we discuss the progress of emerging dry processes for nanoscale fabrication of high-aspect-ratio features, including emerging design technology for manufacturability. Experts in the fields of plasma processing have contributed to addressing the increasingly challenging demands of nanoscale deposition and etching technologies for high-aspect-ratio features. The discussion of our atomic-scale understanding of physicochemical reactions involving ion bombardment and neutral transport presents the major challenges shared across the plasma science and technology community. Focus is placed on advances in fabrication technology that control surface reactions on three-dimensional features, as well as state-of-the-art techniques used in semiconductor manufacturing with a brief summary of future challenges.

Abstract In this study, ε-Ga 2 O 3 thin films were grown by mist chemical vapor deposition on a hexagonal (0001) GaN template and a cubic (111) SrTiO 3 (STO) substrate. By analyzing the obtained X-ray diffraction (XRD) φ-scans, it was found that the ε-Ga 2 O 3 epitaxial thin films grown on both GaN and STO exhibited an orthorhombic structure. In addition, a method was proposed to distinguish between hexagonal and orthorhombic structures on the basis of the relationships between the 2θ and χ angles for these structures, obtained from the XRD studies. Finally, a mechanism was discussed on the basis of angle relationships, where three rotational domains were observed for orthorhombic ε-Ga 2 O 3 on GaN and STO. Transmission electron microscopy was then employed to determine whether the ε-Ga 2 O 3 thin films on the GaN template and STO substrate consisted of columnar ε-Ga 2 O 3 comprising small domains and intermediate layers between the ε-Ga 2 O 3 film and the substrate.

Abstract In recent years, piezoelectric microelectromechanical systems (MEMS) have attracted attention as next-generation functional microdevices. Typical applications of piezoelectric MEMS are micropumps for inkjet heads or micro-gyrosensors, which are composed of piezoelectric Pb(Zr,Ti)O 3 (PZT) thin films and have already been commercialized. In addition, piezoelectric vibration energy harvesters (PVEHs), which are regarded as one of the key devices for Internet of Things (IoT)-related technologies, are promising future applications of piezoelectric MEMS. Significant features of piezoelectric MEMS are their simple structure and high energy conversion efficiency between mechanical and electrical domains even on the microscale. The device performance strongly depends on the function of the piezoelectric thin films, especially on their transverse piezoelectric properties, indicating that the deposition of high-quality piezoelectric thin films is a crucial technology for piezoelectric MEMS. On the other hand, although the difficulty in measuring the precise piezoelectric coefficients…

Abstract The electrical properties of ferroelectric Hf–Zr–O ultrathin films, particularly the dependences of remnant polarization, leakage current, coercive field, and breakdown field on the metal composition and film thickness, are systematically examined. Physical analyses show that the Hf–Zr–O films in this experiment consist of polycrystalline grains and contain both ferroelectric and dielectric phases. It is found that changes in metal composition and thickness strongly influence the remnant polarization and the leakage current simultaneously. In contrast, the coercive field was relatively unaffected by these parameters. This particular behavior of the coercive field suggests that the polarization switching in Hf–Zr–O films is predominantly determined by the nature of nanometer-scale ferroelectric domains dispersed in the films.

Abstract In this paper, the use of a structure comprising a thin LiNbO 3 plate and a multilayered acoustic mirror composed of SiO 2 and Pt for high-performance longitudinal leaky surface acoustic wave (LLSAW) device is proposed. The mirror is expected to offer a much higher reflectivity than that composed of SiO 2 and AlN, which the authors proposed previously. The field distribution of these structures is calculated by using a finite element method. It is shown that the acoustic wave energy of the proposed structure is well confined in the vicinity of the top surface, and that leakage to the substrate is reduced. A one-port resonator is fabricated on the structure and its performance characteristics are evaluated. Owing to a high phase velocity of 6,035 m/s, which is about 1.5 times higher than that of conventional SAWs, a large impedance ratio of 71 dB was achieved at 3.5 GHz in addition to a large fractional bandwidth of 9.5%.

Abstract Corundum-structured oxides have been attracting much attention as next-generation power device materials. A corundum-structured α-Ga 2 O 3 successfully demonstrated power device operations of Schottky barrier diodes (SBDs) with the lowest on-resistance of 0.1 mΩ cm 2 . The SBDs as a mounting device of TO220 also showed low switching-loss properties with a capacitance of 130 pF. Moreover, the thermal resistance was 13.9 °C/W, which is comparable to that of the SiC TO220 device (12.5 °C/W). On the other hand, corundum-structured α-(Rh,Ga) 2 O 3 showed p-type conductivity, which was confirmed by Hall effect measurements. The Hall coefficient, carrier density, and mobility were 8.22 cm 3 /C, 7.6 × 10 17 /cm 3 , and 1.0 cm 2 V −1 s −1 , respectively. These values were acceptable for the p-type layer of pn diodes based on α-Ga 2 O 3 .

Abstract “Hetero acoustic layer (HAL) surface acoustic wave (SAW) device” is a new type of SAW device using a single crystal piezoelectric thin plate supported by a substrate. In this study, a HAL SAW resonator using a LiNbO 3 (LN) thin plate and a multi-layer acoustic film was designed by finite element method (FEM) and fabricated. The thickness of LN is 3.6 µm and the pitch of an interdigital transducer (IDT) (λ) is 5.24 µm for a resonance frequency of 600 MHz. The multi-layer acoustic film is composed of 3 layers of SiO 2 and AlN for each, i.e., 6 layers in total, alternately deposited on a glass substrate. The HAL SAW resonator achieved a wide bandwidth of 20.3% and a high impedance ratio of 83 dB. Compared with a 0th shear horizontal (SH 0 ) mode plate wave resonator, the performance is better and the thickness of LN is 7 times larger. The HAL SAW without a cavity is advantageous in terms of mechanical stability, thickness controllability and fabrication yield.

Abstract We demonstrate zero-bias spectral responsivity in MBE-grown β-Ga 2 O 3 planar UV-C detector with good linearity up to optical power density of 4.6 mW cm −2 . Devices with asymmetrical metal contacts were realized on 150 nm thick β-Ga 2 O 3 films on sapphire. The device exhibited a spectral responsivity of 1.4 mA W −1 at 255 nm under zero-bias condition, dark current <10 nA at 15 V and UV-to-visible rejection ratio ∼10 5 at 5 V. The demonstrated UV-C detector exhibited an estimated high detectivity of 2.0 × 10 12 Jones at 1 V and were found to be very stable and repeatable, suggesting its potential use for focal plane arrays.

Abstract We demonstrated the grain size effect on piezoelectric properties of pure BaTiO 3 ceramics. BaTiO 3 ceramics with various grain sizes were prepared by conventional and two-step sintering methods. The piezoelectric strain constant d 33 increased with decreasing grain size when the grain size was more than 1.2 µm, whereas it decreased when the grain size was below 1.2 µm. The maximum d 33 was 460 pC/N, which is approximately three times larger than that of coarse BaTiO 3 ceramics. The increase in d 33 was well explained by the domain-wall contribution, while the decrease in d 33 was understood as the grain boundary effect. On the other hand, the piezoelectric voltage constant g 33 increased with decreasing grain size down to 0.6 µm. The piezoelectric constants d 33 and g 33 , and the mechanical quality factor Q m can be controlled by the grain size of BaTiO 3 ceramics.

Abstract We employ simulation based approach for enhancing the efficiency of Cu 2 ZnSnS 4 (CZTS) based solar cells. Initial benchmarking of simulation with the experimentally reported solar cell in literature is performed by incorporating a suitable defect model. We then explore the effects of (a) conduction band offset (CBO) at CZTS/CdS junction, (b) back surface field (BSF) due to an additional layer with higher carrier density, and (c) high work function back contact. Efficiency is observed to improve by about 70% upon optimizing the above three parameters. We also observe that utilizing BSF in the configuration can reduce the high work function requirement of the back contact. A work function of 5.2 eV (e.g., using Ni), a BSF layer (e.g., using SnS), and a CBO of 0.1 eV (e.g., using ZnS) constitute an optimal configuration.

Abstract We report on the electrical characterization of Si-ion implanted AlN layers and the first demonstration of metal–semiconductor field-effect transistors (MESFETs) with an ion-implanted AlN channel. The ion-implanted AlN layers with Si dose of 5 × 10 14 cm −2 exhibit n-type characteristics after thermal annealing at 1230 °C. The ion-implanted AlN MESFETs provide good drain current saturation and stable pinch-off operation even at 250 °C. The off-state breakdown voltage is 2370 V for drain-to-gate spacing of 25 µm. These results show the great potential of AlN-channel transistors for high-temperature and high-power applications.

Abstract The structural stabilities of perovskite compounds were investigated by calculating the tolerance and octahedral factors, which are known as the empirical indexes of the stabilities of the perovskite structure. Elements of groups 2, 12, and 14, and transition metals were substituted in CH 3 NH 3 PbI 3 compounds, and the ranges of compositions with a perovskite structure were proposed. 540 compounds were surveyed in this work, 132 of which were used to satisfy the conditions of forming the perovskite structure. Of these 132 compounds, 83 were candidates for low-toxicity compounds.

Abstract Metal halide perovskites can be easily fabricated with low-temperature solution processes, and they are a promising class of materials for solar cells, light emitters, and nonlinear optical devices. The perovskites are direct-gap semiconductors with sharp absorption edges and a highly efficient luminescence with no Stokes shift. In addition, the perovskites exhibit superior optoelectronic properties such as efficient photon recycling and long free-carrier diffusion. In this review, we discuss the fundamental optical properties of bulk crystals and the operation principles of heterodiode devices based on these novel functional materials.

Abstract We present a novel route for the adsorption of pulsed laser-dispersed nanoparticles onto metal powders in aqueous solution without using any binders or surfactants. By electrostatic interaction, we deposit Y 2 O 3 nanoparticles onto iron–chromium based powders and obtain a high dispersion of nano-sized particles on the metallic powders. Within the additively manufactured component, we show that the particle spacing of the oxide inclusion can be adjusted by the initial mass fraction of the adsorbed Y 2 O 3 particles on the micropowder. Thus, our procedure constitutes a robust route for additive manufacturing of oxide dispersion-strengthened alloys via oxide nanoparticles supported on steel micropowders.

Abstract Pyrochlore La 2 Hf 2 O 7 , Gd 2 Hf 2 O 7 , and Lu 2 Hf 2 O 7 single crystals were successfully grown by using an optical floating zone furnace. The synthesized crystals exhibit scintillation with a broad emission peaking around 440–510 nm. The crystal quality and luminescence intensity are sufficiently high that it is applicable for pulse height spectrum measurements. Under 241 Am alpha-ray exposure, the pulse height spectrum indicates the estimated light yield of a La 2 Hf 2 O 7 crystal is 270 photons/MeV.

Abstract The band alignment at an α-Ga 2 O 3 /α-(Al x Ga 1− x ) 2 O 3 heterointerface, with different Al compositions ( x ), grown on a c -plane sapphire substrate was evaluated by X-ray photoelectron spectroscopy. The experimental results show that the heterointerface has the type-I band discontinuity with the valence band offsets of 0.090, 0.12, and 0.14 eV, and the conduction band offsets of 0.34, 0.79, and 1.87 eV, for x values of 0.1, 0.4, and 0.8, respectively. The small band offset for the valence band is attributed to the fact that the valence band of oxides is constituted by the localized O 2p level, which is dominated by the nature of oxygen atoms. The type-I band discontinuity is desirable for a variety of heterostructure devices.

Abstract We studied hole generation in Mg-doped AlN/Al 0.75 Ga 0.25 N superlattices (SLs) with an average Al content of 0.8. High hole concentrations on the order of 10 18 cm −3 were obtained in the SLs. The temperature dependence of the hole concentration indicated an effective acceptor ionization energy of 40–67 meV, which is much lower than that of Mg-doped Al 0.8 Ga 0.2 N alloy (>400 meV). The hole concentration increased with increasing SL period thickness and became almost constant at about 30 nm. These results indicate that the band bending caused by strong spontaneous and piezoelectric polarization fields enhances the ionization of the Mg acceptors.

Abstract Single-photon detection and photon counting are useful tools in many fields, from light detection and ranging (LiDAR) to biomedical imaging and from time-resolved Raman spectroscopy to quantum applications. In this context, recently, single-photon avalanche diode (SPAD) sensors in standard CMOS technology have been receiving considerable attention from both scientific and industrial communities since they can provide single-photon detection and photon-counting capabilities along with some functionalities such as time-of-arrival evaluation and histogram processing in a cost-effective manner. In this review, we provide a comprehensive view of the CMOS SPAD technology: from fundamentals to cutting-edge technologies including three-dimensional (3D)-stacked CMOS SPAD sensors.

Abstract We have been working on the fabrication of practical perovskite solar modules using an existing thin-film solar module patterning technology. Patterning processes were applied using laser scribing and mechanical scribing on a glass/F-doped SnO 2 (FTO)/compact TiO 2 (c-TiO 2 )/meso-TiO 2 /CH 3 NH 3 PbI 3 /2,2′,7,7′-tetrakis( N , N -di- p -methoxyphenylamine)-9,9′-spirobifluorene/Au structure. However, TiO 2 remained in the FTO–Au junction at the cell connection part: this appeared to create a series resistance that degraded the performance of the module. UV laser treatment was examined for application to the cell connection part to minimize this resistance. The results showed that the resistivity of the cell connection part, which was conventionally 0.26 Ω·cm 2 , was reduced to 0.1 Ω·cm 2 by this laser treatment. We designed the solar module based on the value of a contact resistivity of 0.1 Ω·cm 2 and the current–voltage curve of a small single cell. As a result of prototyping solar cell modules (35 cells in series) with an aperture area of 354 cm 2 on a 203 × 203 mm 2…

Abstract Improving the light-extraction efficiency (LEE) is a major issue for the development of deep-ultraviolet (DUV) light-emitting diodes (LEDs). For this improvement, we introduced a transparent p-AlGaN contact layer and a reflective p-type electrode. In this work, we investigated the improvements obtained by replacing conventional Ni/Au p-type electrodes with highly reflective Ni/Mg and Rh electrodes. The external quantum efficiencies (EQEs) of 279 nm DUV LEDs were increased from 4.2 to 6.6% and from 3.4 to 4.5% by introducing Ni/Mg and Rh p-type electrodes, respectively. The LEE enhancement factors for the Ni/Mg and Rh electrodes were 1.6 and 1.4, respectively. These results are explained by the fact that the measured reflectances of the Ni/Mg and Rh electrodes were approximately 80 and 55%, respectively. Moreover, it was concluded that a passivation layer is required for Ni/Mg electrodes to prevent the degradation of the LED properties by the oxidation of Mg.

Abstract The power conversion efficiencies of single-junction III–V solar cells based on InGaP, GaAs, InGaAsP, and InGaAs for wireless power transmission were investigated by varying the wavelength and incident power of a laser diode. The GaAs solar cell exhibited the highest conversion efficiency of 52.7% at a laser wavelength of 824 nm and a laser beam irradiance of 4 suns. For each solar cell, the conversion efficiency peaked at an optimal incident laser wavelength and this effect was examined in detail. It was found that the conversion efficiency is maximal when the laser photon energy is 80–100 meV higher than the bandgap of the semiconductor material.

Abstract This paper discusses the opportunities and challenges of designing products using luminescent solar concentrator (LSC) photovoltaic (PV) technologies. The focus is on the integration of LSC PV technologies in PV modules, future products and buildings. It is shown that the typical material properties of LSCs — low cost, colorful, bendable, and transparency — offer a lot of design freedom. Two differently designed LSC PV modules with back contacted solar cells are presented including ray-tracing simulations and experimental results resulting from their prototypes. It is shown that the efficiency of a LSC PV module can be 5.8% with a maximum efficiency of 10%. Further the results of a design study which focused on product integration of LSC PV technologies are presented and discussed. In total 16 different and highly innovative conceptual designs resulted from this project, which were prototyped at scale to show their feasibility and integration features.

Abstract We have succeeded in experimentally observing the memory functionality of a vortex-type spin torque oscillator used in recurrent neural networks for the first time. Voltage pulses representing random binary pattern of 2000 (1000) bits were applied to the oscillator for learning (test), and the amplitude of the oscillator was evaluated as the 200 virtual nodes. The memory capacity of the whole system including the oscillator was evaluated to be 1.8 at maximum. The value is larger than the memory capacity of the system without the oscillator, indicating the existence of a finite contribution from the spin torque oscillator.

Abstract In this study, the experimental evaluation and numerical analysis of short-circuit mechanisms of 1200 V SiC planar and trench MOSFETs were conducted at various DC bus voltages from 400 to 800 V. Investigation of the impact of DC bus voltage on short-circuit capability yielded results that are extremely useful for many existing power electronics applications. Three failure mechanisms were identified in this study: thermal runaway, MOS channel current following device turn-off, and rupture of the gate oxide layer (gate oxide layer damage). The SiC MOSFETs experienced lattice temperatures exceeding 1000 K during the short-circuit transient; as Si insulated gate bipolar transistors (IGBTs) are not typically subject to such temperatures, the MOSFETs experienced distinct failure modes, and the mode experienced was significantly influenced by the DC bus voltage. In conclusion, suggestions regarding the SiC MOSFET design and operation methods that would enhance device robustness are proposed.

Abstract On the basis of a novel crystal hardness control, we successfully realized macrodefect-free, large (2–6 in.) and thick + c -oriented GaN bulk crystals by hydride vapor phase epitaxy. Without the hardness control, the introduction of macrodefects including inversion domains and/or basal-plane dislocations seemed to be indispensable to avoid crystal fracture in GaN growth with millimeter thickness. However, the presence of these macrodefects tended to limit the applicability of the GaN substrate to practical devices. The present technology markedly increased the GaN crystal hardness from below 20 to 22 GPa, thus increasing the available growth thickness from below 1 mm to over 6 mm even without macrodefect introduction. The 2 and 4 in. GaN wafers fabricated from these crystals had extremely low dislocation densities in the low- to mid-10 5 cm −2 range and low off-angle variations (2 in.: <0.1°; 4 in.: ∼0.2°). The realization of such high-quality 6 in. wafers is also expected.

Abstract We have fabricated turbostratic stacked graphene with high-transport properties by the repeated transfer of CVD monolayer graphene. The turbostratic stacked CVD graphene exhibited higher carrier mobility and conductivity than CVD monolayer graphene. The electron mobility for the three-layer turbostratic stacked CVD graphene surpassed 10,000 cm 2 V −1 s −1 at room temperature, which is five times greater than that for CVD monolayer graphene. The results indicate that the high performance is derived from maintenance of the linear band dispersion, suppression of the carrier scattering, and parallel conduction. Therefore, turbostratic stacked CVD graphene is a superior material for high-performance devices.

Abstract Different concepts for active windows for dynamic light regulation and vibrant climatization support in buildings are compared, followed by a MEMS concept using millions of micromirrors inside insulation or vacuum glazing to guide and control light by electrostatic mirror actuation. The concept enables energy saving, tailored personalized lighting, security, and smart personalized environments in buildings. The window transmission is controlled continuously, showing the eye a variable-tone pane. The amount, direction, and degree of steering of the guided light are tailored to winter, summer, and variable daytime requirements, protecting rooms and persons inside from sun-light while providing tailored natural daylight illumination. The concept is based on reflection, in contrast to existing concepts based on absorption. These micromirror arrays have been designed, fabricated, and characterized. Experimental results on electrostatic actuation voltages, extrapolated lifetime, power consumption, and heat impact regulation are presented.

The minimum specific on-resistance of 4H-SiC{0001} unipolar devices as a function of the breakdown voltage was updated based on latest studies on intrinsic physical properties, such as impact ionization coefficients. Both punch-through (PT) and nonpunch-through (NPT) structures were considered, because a PT structure generally gives a lower on-resistance at a given breakdown voltage. The minimum specific on-resistance of 1 kV 4H-SiC devices can be as low as 0.20 mΩ cm 2 at room temperature. An analytical expression for the relationship between the specific on-resistance and breakdown voltage is given.

Abstract Vertical-cavity surface-emitting laser (VCSEL) diodes provide extraordinary properties like sub-mA threshold current, multi-GHz modulation capability, or relative intensity noise close to the quantum limit. VCSEL diodes have become a preferred light source for optical sensor technologies and imaging systems. The purpose is to review some recent developments with special attention to mass market employments and to reveal future applications.

Abstract The advanced progress of electronic-based devices for artificial neural networks and recent trends in neuromorphic engineering are discussed in this review. Recent studies indicate that the memristor and transistor are two types of devices that can be implemented as neuromorphic devices. The electrical switching characteristics and physical mechanism of neuromorphic devices based on metal oxide, metal sulfide, silicon, and carbon materials are broadly covered in this review. Moreover, the switching performance comparison of several materials mentioned above are well highlighted, which would be useful for the further development of memristive devices. Recent progress in synaptic devices and the application of a switching device in the learning process is also discussed in this paper.

Abstract Ferroelectric random access memory (FRAM) has been commercialized for about 20 years and its reliability has been well proven all over the world. In the recent Internet of Things (IoT) era, it also plays important roles to particularly in edge computing because of its high writing speed, high rewriting endurance, and low writing energy consumption. We review the history of semiconductor memories using ferroelectrics and overview the progresses of the new ferroelectrics and promising ferroelectric applications in the future.

Abstract This paper reviews the main research results related to PERC+ silicon solar cells. Compared to today’s industry typical passivated emitter and rear cell (PERC) silicon solar cells with full-area rear aluminum layer, PERC+ solar cells apply an aluminum finger grid on the rear side and hence are able to absorb diffuse light from the rear side in addition to the direct sunlight which is absorbed from the front side. This bifaciality increases the energy yield of silicon solar modules by up to 25%. Since its first publication in 2015, the PERC+ cell concept has been rapidly adopted by several solar cell manufacturers due to the very similar process technology of bifacial PERC+ cells and main stream monofacial PERC cells. We summarize technological challenges, published PERC+ conversion efficiencies and PERC+ module technologies. First energy yield data of PERC+ field installations demonstrate the high energy yield potential of PERC+ solar cells.

Abstract The aerosol deposition (AD) method is a unique approach to metal and ceramic coating, by which solid-state submicron metal and ceramic particles are accelerated by gas flow up to 100–500 m/s and then impacted onto a substrate. The National Institute of Advanced Industrial Science and Technology (AIST) found an interesting consolidation phenomenon of ceramic particles in this method over 20 years ago. During the collision of fine particles and interaction with the substrate, these ceramic particles, not only for oxide materials but also for non-oxide materials, form thick, dense, and hard ceramic layers at room temperature. No additional heating for the solidification of ceramic powder was required. We named this phenomenon “room-temperature impact consolidation (RTIC)”. Consolidated ceramic powder with RTIC via the AD method can be called as a high-density binderless ceramic green. It can rapidly form into a thick dense, uniform, and hard layer at room temperature without additional heating for solidifying starting powders, even at a low vacuum, using relatively cheap and…

Abstract Complexity is an increasingly crucial aspect of societal, environmental and biological phenomena. Using a dense unorganized network of synthetic synapses it is shown that a complex adaptive system can be physically created on a microchip built especially for complex problems. These neuro-inspired atomic switch networks (ASNs) are a dynamic system with inherent and distributed memory, recurrent pathways, and up to a billion interacting elements. We demonstrate key parameters describing self-organized behavior such as non-linearity, power law dynamics, and multistate switching regimes. Device dynamics are then investigated using a feedback loop which provides control over current and voltage power-law behavior. Wide ranging prospective applications include understanding and eventually predicting future events that display complex emergent behavior in the critical regime.

Abstract Rb 2 GeF 6 :Mn 4+ red-emitting phosphors were synthesized by coprecipitation and their structural and optical properties were investigated by laser microscopy observation, X-ray diffraction (XRD) analysis, photoluminescence (PL) analysis, PL excitation (PLE) spectroscopy, and PL decay measurement. Single-crystalline ingots in the form of a hexagonal pyramid were prepared with a basal plane diameter of ∼2 mm. The XRD analysis suggested that Rb 2 GeF 6 crystallizes in the hexagonal structure ( ) with a = 0.5955 nm and c = 0.9672 nm. The phosphor exhibited the strong Mn 4+ -related zero-phonon line (ZPL) emission peak typically observed in host crystals with piezoelectrically active lattices such as a hexagonal lattice. The quantum efficiencies of the bulk ingot and powdered samples were 87 and 74%, respectively, with nearly the same luminescence decay time of ∼6 ms. The exact ZPL energies and related crystal-field and Racah parameters were obtained from the PL and PLE spectra by Franck–Condon analysis. Temperature-dependent PL intensities were analyzed from T = 20 to 500 K…

Abstract The temperature dependence of impact ionization coefficients of electrons and holes along 4H-SiC 〈0001〉 was determined in a wide temperature range from 156 K to 561 K. Photomultiplication measurements were conducted using several types of 4H-SiC photodiodes (PDs) with different structures under high vacuum conditions. The hole ionization coefficient showed a negative temperature dependence, which can be attributed to enhanced phonon scattering at elevated temperatures. Temperature dependence of the electron ionization coefficient was small, and this result may be ascribed to the simultaneous effects of enhanced phonon scattering and shrinkage of minigaps in the conduction band. Accuracy of the obtained results was verified by comparing the calculated breakdown voltage with the experimental breakdown voltage of various diodes.

Abstract The origin of expanded single Shockley-type stacking faults in forward-current degradation of 4H-SiC p–i–n diodes was investigated by the stress-current test. At a stress-current density lower than 25 A cm −2 , triangular stacking faults were formed from basal-plane dislocations in the epitaxial layer. At a stress-current density higher than 350 A cm −2 , both triangular and long-zone-shaped stacking faults were formed from basal-plane dislocations that converted into threading edge dislocations near the interface between the epitaxial layer and the substrate. In addition, the conversion depth of basal-plane dislocations that expanded into the stacking fault was inside the substrate deeper than the interface. These results indicate that the conversion depth of basal-plane dislocations strongly affects the threshold stress-current density at which the expansion of stacking faults occurs.

Abstract Precise lattice constant measurements based on the Bond method for various types of diamond were performed with a recently reported compensation technique. For the measurements, a calibrated Si single crystal was used as a reference; it was placed in a chamber whose temperature was carefully controlled below the standard deviation σ of ±0.1 °C, including thermo-couple fluctuation of ±0.06 °C for ±σ, X-ray wavelength calibration was performed using the monochromator temperature. A calibration was also carried out for the instrumental value depending on the Bragg angle and it was applied to the 004 diffraction peak of diamond. The lattice constant of high quality insulating undoped IIa type diamond was 3.567095 ± 0.000017 Å (±2σ), which was larger than the previous data derived without above mentioned calibrations. The measurements were carried out for various types of diamond including high pressure high temperature (HPHT) grown crystals as well as crystals grown by the chemical vapor deposition (CVD) method.

Abstract The propagation properties and resonance characteristics of leaky surface acoustic waves (LSAWs) and longitudinal-type LSAWs (LLSAWs) on a LiTaO 3 (LT) thin plate bonded to an AT-cut quartz substrate were investigated experimentally. For the LSAWs and LLSAWs, the bonded structures of 36° Y -cut X -propagating LT (36°YX-LT)/AT-cut 90° X -propagating quartz (AT90°X-quartz) and X -cut 31° Y -propagating LT (X31°Y-LT)/AT-cut 45° X -propagating quartz (AT45°X-quartz) were fabricated, respectively. For the LSAW on 36°YX-LT/AT90°X-quartz, the electromechanical coupling factor ( K 2 ) of 11.1% was obtained at an LT thin-plate thickness of 0.25 wavelength, whereas K 2 for a single LT substrate was measured to be 5.7%. For the LLSAW on X31°Y-LT/AT45°X-quartz, K 2 increased from 2.8% for the single LT substrate to 7.2% at an LT thin-plate thickness of 0.14 wavelength. Furthermore, K 2 of approximately 12% and the temperature coefficient of frequency (TCF) of 0 ppm/°C were theoretically obtained simultaneously for the LSAW on 36°YX-LT/AT-cut 90°X-quartz at a certain thin-plate…

Abstract We investigated the ability of a photo-assisted electrochemical (PEC) etching process to remove the damage that dry etching causes in the near-surface region of GaN samples. The process consists of anodic oxidation of the GaN surface and subsequent dissolution of the oxide with a chemical treatment, and the extent of the PEC reactions depends on the total charge density transferred in them. The PEC process was conducted for samples prepared with various dry-etching conditions followed by fabrication of Schottky barrier diodes (SBDs) and metal–insulator–semiconductor (MIS) capacitors. The PEC process greatly improved the barrier height, ideality factor, and reverse leakage current of SBDs. Capacitance–voltage measurements of MIS capacitors revealed that the densities of interface states and discrete traps were both reduced by the PEC process. The results obtained here show that the PEC process can remove dry-etching damage from the GaN surface.

Abstract The transition metal oxide family harbors various types of materials of interest for spintronics: half-metallic manganites are highly efficient spin injectors and detectors, yielding record values of tunnel magnetoresistance; multiferroic materials, and in particular BiFeO 3 , allow the electrical control of magnetization and spin excitations at room temperature; combined with ferromagnets, piezoelectric perovskites enable a controlled tuning of magnetic anisotropy, domain dynamics and even magnetic order. In this review, we argue that a new opportunity is emerging for oxides in spintronics with the rise of spin–orbit-driven phenomena such as the direct and inverse spin Hall and Rashba–Edelstein effects. After surveying the few results reported on inverse spin Hall measurements in oxide materials, we describe in depth the physics of SrTiO 3 -based interfaces and their usage for both spin-to-charge and charge-to-spin conversion. Finally, we give perspectives for a more thorough exploration of spin Hall effects in oxides and enhanced conversion ratios in both three- and…

Abstract We aim to develop an ultrasonic tissue characterization method for the follow-up of healing ulcers by diagnosing collagen fibers properties. In this paper, we demonstrated a computer simulation with simulation phantoms reflecting irregularly distributed collagen fibers to evaluate the relationship between physical properties, such as number density and periodicity, and the estimated characteristics of the echo amplitude envelope using the homodyned-K distribution. Moreover, the consistency between echo signal characteristics and the structures of ex vivo human tissues was verified from the measured data of normal skin and nonhealed ulcers. In the simulation study, speckle or coherent signal characteristics are identified as periodically or uniformly distributed collagen fibers with high number density and high periodicity. This result shows the effectiveness of the analysis using the homodyned-K distribution for tissues with complicated structures. Normal skin analysis results are characterized as including speckle or low-coherence signal components, and a nonhealed ulcer…

Abstract Luminescence and scintillation properties of Cs 2 HfBr 6 and Cs 2 ZrBr 6 crystals were investigated using photoluminescence (PL) and radioluminescence (RL) spectroscopies. In the PL spectra, emission bands were observed at 435 and 525 nm for Cs 2 HfBr 6 , and at 530 nm for Cs 2 ZrBr 6 . Corresponding emission bands were observed for RL spectra. The scintillation decay time constants of the Cs 2 HfBr 6 and Cs 2 ZrBr 6 crystals were smaller than those of the corresponding Cs 2 HfCl 6 and Cs 2 ZrCl 6 crystals. The scintillation light yields of Cs 2 HfBr 6 and Cs 2 ZrBr 6 were estimated to be 61,500 and 37,200 photons/MeV, respectively, which are much higher than those of Cs 2 HfCl 6 and Cs 2 ZrCl 6 crystals.

Abstract In this study, we investigated progression of potential-induced degradation (PID) in photovoltaic modules fabricated from n-type-based crystalline-silicon cells with front p + emitters. In PID tests in which a bias of −1000 V was applied to the modules, they started to degrade within 5 s and their degradation saturated within 60 s. This behavior suggested that the PID was caused by positive charge accumulation in the front passivation films. Performing PID tests with a bias of −1500 V revealed that the degradation rate strongly depended on the applied bias whereas the saturation value was independent of the applied bias. Regeneration tests on degraded modules previously subjected to PID tests for durations of 5 and 10 min were performed by applying a positive bias of +1000 V. All the degraded modules completely recovered their performance losses within 60 s regardless of the degradation test duration. On the basis of these results, we proposed that these positive charges originate from positively charged K centers formed by extracting electrons from neutral and negatively…

Abstract In this paper, we report room-temperature bonding of LiNbO 3 (LN) and SiO 2 /Si for the realization of a LN on insulator (LNOI)/Si hybrid wafer. We investigate the applicability of a modified surface activated bonding (SAB) method for the direct bonding of LN and a thermally grown SiO 2 layer. The modified SAB method using ion beam bombardment demonstrates the room-temperature wafer bonding of LN and SiO 2 . The bonded wafer was successfully cut into 0.5 × 0.5 mm 2 dies without interfacial debonding owing to the applied stress during dicing. In addition, the surface energy of the bonded wafer was estimated to be approximately 1.8 J/m 2 using the crack opening method. These results indicate that a strong bond strength can be achieved, which may be sufficient for device applications.