1550 nm wavelength photonic-crystal surface-emitting lasers (PCSELs) are attractive for optical communication and eye-safe sensing applications. In this study, we present InP-based PCSELs featuring a double-lattice photonic-crystal structure designed for high-power single-mode operation at a wavelength of 1550 nm. These PCSELs demonstrate output powers exceeding 300 mW under continuous-wave conditions at 25 °C. Additionally, highly stable single-mode oscillation with a side-mode suppression ratio of over 60 dB is verified at temperatures from 15 °C to 60 °C. Measurement and simulation of photonic band structures reveal the impacts of the threshold gain margin and optical coupling coefficient on the single-mode stability.
The Japan Society of Applied Physics
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ISSN: 1882-0786
Applied Physics Express (APEX) is an open access letters journal devoted solely to rapid dissemination of up-to-date and concise reports on new findings in applied physics. The motto of APEX is high scientific quality and prompt publication.
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Takeshi Aoki et al 2024 Appl. Phys. Express 17 042004
Tsunenobu Kimoto and Heiji Watanabe 2020 Appl. Phys. Express 13 120101
Major features of silicon carbide (SiC) power devices include high blocking voltage, low on-state loss, and fast switching, compared with those of the Si counterparts. Through recent progress in the material and device technologies of SiC, production of 600–3300 V class SiC unipolar devices such as power metal-oxide-semiconductor field-effect transistors (MOSFETs) and Schottky barrier diodes has started, and the adoption of SiC devices has been demonstrated to greatly reduce power loss in real systems. However, the interface defects and bulk defects in SiC power MOSFETs severely limit the device performance and reliability. In this review, the advantages and present status of SiC devices are introduced and then defect engineering in SiC power devices is presented. In particular, two critical issues, namely defects near the oxide/SiC interface and the expansion of single Shockley-type stacking faults, are discussed. The current physical understanding as well as attempts to reduce these defects and to minimize defect-associated problems are reviewed.
Masafumi Yokoyama et al 2024 Appl. Phys. Express 17 055502
We have developed a pore-assisted separation (PAS) method for the fabrication of free-standing GaN substrates, where bulk GaN crystals were separated from seed GaN templates at electrochemically formed porous layers. The pore size was controlled by the electrochemical process conditions and must be greater than 100 nm to realize separation within whole wafers. A 2 inch free-standing GaN substrate having a low dislocation density of ∼2.7 × 106 cm−2 was realized by growth of an 800 μm thick GaN layer on the porous GaN template. A 3 inch free-standing GaN substrate was also fabricated by the PAS method, indicating its good scalability.
Haruna Kaneko et al 2024 Appl. Phys. Express 17 053001
Stochastic magnetic tunnel junctions (s-MTJs) are attracting attention as key elements for spintronics-based probabilistic (p-) computers. The performance of p-computers is governed by the time-domain and the time-averaged response of single s-MTJs varying with temperature. Here we present results of the time-domain (rf) voltage and time-averaged (dc) resistance of s-MTJs with perpendicular magnetization as functions of perpendicular magnetic fields Hz and temperatures T = 20 °C–130 °C. We observe that both relaxation time (time-domain response) and the slope of the – curve (time-averaged response) decrease with increasing temperature. We discuss the physics underlying these results including the thermally induced spatially non-uniform collective spin dynamics.
Ryosuke Okumura et al 2024 Appl. Phys. Express 17 041003
Efficient reverse intersystem crossing (RISC) is an important process for thermally activated delayed fluorescence (TADF) to suppress efficiency roll-off in organic LEDs (OLEDs). Enhancing spin–orbit coupling is effective for fast RISC and is achieved by mediating a locally excited triplet state when RISC occurs between charge transfer states. Here, we experimentally confirmed that efficient RISC occurred in triarylborane-based TADF emitters named Phox-Meπ, Phox-MeOπ, and MeO3Ph-FMeπ. The three emitters showed large RISC rate constants exceeding 106 s−1. The Phox-Meπ-based OLED exhibited higher maximum external quantum efficiency (EQEmax = 10.0%) compared to the Phox-MeOπ-based OLED (EQEmax = 6.7%).
J. Koga et al 2024 Appl. Phys. Express 17 042007
Transition metal dichalcogenides with superperiodic lattice distortions have been widely investigated as the platform of ultrafast structural phase manipulations. Here we performed ultrafast electron diffraction on RT TaTe2, which exhibits a peculiar double zigzag chain pattern of Ta atoms. From the time-dependent electron diffraction pattern, we revealed a photoinduced change in the crystal structure occurring within <0.5 ps, although there is no corresponding high-temperature equilibrium phase. We further clarified the slower response (∼1.5 ps) reflecting the lattice thermalization. Our result suggests the unusual ultrafast crystal structure dynamics specific to the non-equilibrium transient process in TaTe2.
Dany Lachance-Quirion et al 2019 Appl. Phys. Express 12 070101
Engineered quantum systems enabling novel capabilities for computation and sensing have blossomed in the last decade. Architectures benefiting from combining complementary physical systems have emerged as promising approaches for quantum technologies. A new class of hybrid quantum systems based on collective spin excitations in ferromagnetic materials has led to the diverse set of platforms outlined in this review article. The coherent interaction between microwave cavity modes and spin-wave modes is presented as a key ingredient for the development of more complex hybrid systems. Indeed, quanta of excitation of the spin-wave modes, called magnons, can also interact coherently with optical photons, phonons, and superconducting qubits in the fields of cavity optomagnonics, cavity magnomechanics, and quantum magnonics, respectively. Notably, quantum optics experiments in magnetically-ordered solid-state systems are within reach thanks to quantum magnonics. Applications of hybrid quantum systems based on magnonics for quantum information processing and quantum sensing are briefly outlined.
Fumiyasu Oba and Yu Kumagai 2018 Appl. Phys. Express 11 060101
Recent first-principles approaches to semiconductors are reviewed, with an emphasis on theoretical insight into emerging materials and in silico exploration of as-yet-unreported materials. As relevant theory and methodologies have developed, along with computer performance, it is now feasible to predict a variety of material properties ab initio at the practical level of accuracy required for detailed understanding and elaborate design of semiconductors; these material properties include (i) fundamental bulk properties such as band gaps, effective masses, dielectric constants, and optical absorption coefficients; (ii) the properties of point defects, including native defects, residual impurities, and dopants, such as donor, acceptor, and deep-trap levels, and formation energies, which determine the carrier type and density; and (iii) absolute and relative band positions, including ionization potentials and electron affinities at semiconductor surfaces, band offsets at heterointerfaces between dissimilar semiconductors, and Schottky barrier heights at metal–semiconductor interfaces, which are often discussed systematically using band alignment or lineup diagrams. These predictions from first principles have made it possible to elucidate the characteristics of semiconductors used in industry, including group III–V compounds such as GaN, GaP, and GaAs and their alloys with related Al and In compounds; amorphous oxides, represented by In–Ga–Zn–O; transparent conductive oxides (TCOs), represented by In2O3, SnO2, and ZnO; and photovoltaic absorber and buffer layer materials such as CdTe and CdS among group II–VI compounds and chalcopyrite CuInSe2, CuGaSe2, and CuIn1−xGaxSe2 (CIGS) alloys, in addition to the prototypical elemental semiconductors Si and Ge. Semiconductors attracting renewed or emerging interest have also been investigated, for instance, divalent tin compounds, including SnO and SnS; wurtzite-derived ternary compounds such as ZnSnN2 and CuGaO2; perovskite oxides such as SrTiO3 and BaSnO3; and organic–inorganic hybrid perovskites, represented by CH3NH3PbI3. Moreover, the deployment of first-principles calculations allows us to predict the crystal structure, stability, and properties of as-yet-unreported materials. Promising materials have been explored via high-throughput screening within either publicly available computational databases or unexplored composition and structure space. Reported examples include the identification of nitride semiconductors, TCOs, solar cell photoabsorber materials, and photocatalysts, some of which have been experimentally verified. Machine learning in combination with first-principles calculations has emerged recently as a technique to accelerate and enhance in silico screening. A blend of computation and experimentation with data science toward the development of materials is often referred to as materials informatics and is currently attracting growing interest.
Nozomu Ishiguro et al 2024 Appl. Phys. Express 17 052006
As the first experiment at BL10U in NanoTerasu, tender X-ray ptychographic coherent diffraction imaging (PCDI) was conducted using a photon energy of 3.5 keV. The ptychographic diffraction patterns from a 200 nm thick Ta test chart and a micrometer-sized particle of sulfurized polymer were collected. Subsequently, phase images were reconstructed with resolutions of sub-20 nm and sub-50 nm, respectively. In the near future, tender X-ray PCDI with sub-10 nm resolution is anticipated to potentially revolutionize the visualization of nanoscale structures and chemical states in various functional materials composed of light elements.
Kenjiro Uesugi et al 2024 Appl. Phys. Express 17 042008
Reducing the average Al composition of AlxGa1−xN/AlyGa1−yN multiple quantum wells (MQWs) is an effective approach to increase the current injection efficiencies of far-UV-C LEDs (far-UVC LEDs). A reduction can be realized by decreasing the Al-composition differentiation between the well and barrier layers. Compared to conventional MQWs, a 230 nm wavelength far-UVC LED equipped with a single-Al-composition and a 39 nm thick light-emitting layer exhibits a higher external quantum efficiency (EQE). The EQE of far-UVC LEDs with low Al-composition differentiation (∼1%) is enhanced to approximately 0.6% and 1.4% under continuous wave operations at 230 nm and 236 nm wavelengths, respectively.
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Nozomu Ishiguro et al 2024 Appl. Phys. Express 17 052006
As the first experiment at BL10U in NanoTerasu, tender X-ray ptychographic coherent diffraction imaging (PCDI) was conducted using a photon energy of 3.5 keV. The ptychographic diffraction patterns from a 200 nm thick Ta test chart and a micrometer-sized particle of sulfurized polymer were collected. Subsequently, phase images were reconstructed with resolutions of sub-20 nm and sub-50 nm, respectively. In the near future, tender X-ray PCDI with sub-10 nm resolution is anticipated to potentially revolutionize the visualization of nanoscale structures and chemical states in various functional materials composed of light elements.
Sosuke Iwamoto et al 2024 Appl. Phys. Express 17 051008
We investigated the abundance, structures, energy levels, and spin states of oxygen-related defects in 4H-SiC on the basis of first-principles calculations. We applied a hybrid functional in the overall calculations, which gives reliable defect properties, and also considered relevant defect charge states. We identified the oxygen interstitial (Oi,1), substitutional oxygen (OC), and oxygen-vacancy (OCVSi) complex as prominent defects in n-type conditions. Among them, OCVSi was predicted as a spin-1 defect with NIR emission in a previous study. On the basis of the obtained results, we discuss the possible spin decoherence sources when employing OCVSi as a spin-to-photon interface.
Dan Wu et al 2024 Appl. Phys. Express 17 052007
Nonlinear optical materials, especially two-dimensional materials, are anticipated to reveal broadband optical nonlinearity for future miniaturized photonic applications. Herein, we report a physical vapor deposition method to produce β-In2Se3 thin film and investigate the broadband nonlinear absorption (β) and refraction (n2) characteristics. The β-In2Se3 semiconductor shows an excellent optical nonlinearity with large β in 102 cm GW−1 scale and n2 in 10−12 cm2 W−1 scale from visible to NIR wavelengths, which are superior to those of metal carbides and nitrides (MXenes) and metal-organic frameworks. This excellent optical nonlinearity makes β-In2Se3 a promising candidate for advanced nanophotonic devices and beyond.
Ikki Nagaoka et al 2024 Appl. Phys. Express 17 054501
This study investigates the timing margin required to handle fluctuations and variations in superconductor single-flux-quantum gate-level-pipelined adders; a smaller timing margin would improve the clock frequencies of gate-level-pipelined circuits. To evaluate timing margins, we demonstrated three 4 bit adders with 50-, 75-, and 100 GHz target clock frequencies using a 1.0 μm process. We estimated that the required timing margin of the adders was 2.1 ps. This indicates that previously reported gate-level-pipelined circuits operating at 30–60 GHz could operate at higher clock frequencies by reducing the timing margins.
Gulzar Ali J et al 2024 Appl. Phys. Express 17 052005
The work examines terahertz (THz) broadband absorbers for unit topological structure (UTS) with spaced graphene. This study examined the transmission and absorption of the proposed structure without and with graphene at each dielectric interface. The UTS absorbed more light while using a cascade structure with a structural index (n) and adjusting dielectric thicknesses (Δ). Absorption increased significantly with an external magnetic field (B). The objective for a complete THz absorber is achieved with average absorption, = 0.8093 by a modified structure with n = 5, applying an external magnetic field, B = 10.7 T, Fermi level, EF = −0.48 eV, and manipulating the thickness parameter Δ.
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Takashi Tsuchiya et al 2022 Appl. Phys. Express 15 100101
An emerging concept of "nanoarchitectonics" has been proposed as a way to apply the progress of nanotechnology to materials science. In the introductory parts, we briefly explain the progress in understanding materials through nanotechnology, the overview of nanoarchitectonics, the effects of nanoarchitectonics on the development of functional materials and devices, and outline of nanoarchitectonics intelligence as a main subject of this review paper. In the following sections, we explain the process of constructing intelligent devices based on atomic switches, in which the behavior of atoms determines the device functions, by integrating them with nanoarchitectonics. The contents are categorized into (i) basic operation of atomic switch, (ii) artificial synapse, (iii) neuromorphic network system, (iv) hetero-signal conversion, (v) decision making device, and (vi) atomic switch in practical uses. The atomic switches were originally relatively simple ON/OFF binary-type electrical devices, but their potential as multi-level resistive memory devices for artificial synapses and neuromorphic applications. Furthermore, network-structured atomic switches, which are complex and have regression pathways in their structure and resemble cranial neural circuits. For example, A decision-making device that reproduces human thinking based on a principle different from brain neural circuits was developed using atomic switches and proton-conductive electrochemical cells. Furthermore, atomic switches have been progressively developed into practical usages including application in harsh environments (e.g. high temperature, low temperature, space). Efforts toward information processing and artificial intelligence applications based on nanoarchitectonics tell remarkable success stories of nanoarchitectonics, linking the control of atomic motion to brain-like information control through nanoarchitecture regulations.
Masateru Taniguchi 2022 Appl. Phys. Express 15 070101
Nanopores are cost-effective digital platforms, which can rapidly detect and identify biomolecules at the single-molecule level with high accuracy via the changes in ionic currents. Furthermore, nanoscale deoxyribonucleic acid and proteins, as well as viruses and bacteria that are as small as several hundred nanometers and several microns, respectively, can be detected and identified by optimizing the diameters of a nanopore according to the sample molecule. Thus, this review presents an overview of the methods for fabricating nanopores, as well as their electrical properties, followed by an overview of the transport properties of ions and analyte molecules and the methods for electrical signal analysis. Thus, this review addresses the challenges of the practical application of nanopores and the countermeasures for mitigating them, thereby accelerating the construction of digital networks to secure the safety, security, and health of people globally.
Shohei Kumagai et al 2022 Appl. Phys. Express 15 030101
The past several decades have witnessed a vast array of developments in printable organic semiconductors, where successes both in synthetic chemistry and in printing technology constituted a key step forward to the realization of printed electronics. In this Review, we highlight specifically materials science, charge transport, and device engineering of—two-dimensional single crystals—. Defect-free organic single-crystalline wafers manufactured via a one-shot printing process allow remarkably reliable implementations of organic thin-film transistors with decently high carrier mobility up to 10 cm2 V−1 s−1, which has revolutionized the current printing electronics to be able to meet looming internet of things challenges. This Review focuses on the perspective of printing two-dimensional single crystals with reasonable areal coverage, showing their promising applications for practical devices and future human society, particularly based on our recent contributions.
Tsunenobu Kimoto and Heiji Watanabe 2020 Appl. Phys. Express 13 120101
Major features of silicon carbide (SiC) power devices include high blocking voltage, low on-state loss, and fast switching, compared with those of the Si counterparts. Through recent progress in the material and device technologies of SiC, production of 600–3300 V class SiC unipolar devices such as power metal-oxide-semiconductor field-effect transistors (MOSFETs) and Schottky barrier diodes has started, and the adoption of SiC devices has been demonstrated to greatly reduce power loss in real systems. However, the interface defects and bulk defects in SiC power MOSFETs severely limit the device performance and reliability. In this review, the advantages and present status of SiC devices are introduced and then defect engineering in SiC power devices is presented. In particular, two critical issues, namely defects near the oxide/SiC interface and the expansion of single Shockley-type stacking faults, are discussed. The current physical understanding as well as attempts to reduce these defects and to minimize defect-associated problems are reviewed.
Dany Lachance-Quirion et al 2019 Appl. Phys. Express 12 070101
Engineered quantum systems enabling novel capabilities for computation and sensing have blossomed in the last decade. Architectures benefiting from combining complementary physical systems have emerged as promising approaches for quantum technologies. A new class of hybrid quantum systems based on collective spin excitations in ferromagnetic materials has led to the diverse set of platforms outlined in this review article. The coherent interaction between microwave cavity modes and spin-wave modes is presented as a key ingredient for the development of more complex hybrid systems. Indeed, quanta of excitation of the spin-wave modes, called magnons, can also interact coherently with optical photons, phonons, and superconducting qubits in the fields of cavity optomagnonics, cavity magnomechanics, and quantum magnonics, respectively. Notably, quantum optics experiments in magnetically-ordered solid-state systems are within reach thanks to quantum magnonics. Applications of hybrid quantum systems based on magnonics for quantum information processing and quantum sensing are briefly outlined.
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Ahmed et al
Drag between the electron-layer and the hole-layer formed in a silicon-on-insulator metal-oxide-semiconductor field-effect-transistor, with the estimated interlayer distance as small as 18 nm, is investigated. The drag resistance is measured at 10 K and mapped on the plane defined by the electron density and hole density. The analysis shows that the Coulomb drag predominates over the competing virtual-phonon drag. The observed drag resistance is as large as 103 - 104 Ω, indicating strong Coulomb interaction between the electron and hole layers.
Ayukawa et al
High-quality epitaxial Mg3Sb2 thin films are promising thermoelectric materials to enable practical applications of compact and environmentally friendly thermoelectric conversion at room temperature. In this study, high-quality single-crystal Mg3Sb2 with high c-plane orientation were epitaxially grown directly on annealed c-Al2O3 substrates without passive layers. These thin films exhibited three times higher thermoelectric power factor than ever reported values due to high carrier mobility. The ultra-smooth surface of the annealed c-Al2O3 substrate facilitated the formation of high-quality Mg3Sb2 thin films without passive layers or polycrystalline interfaces that could be carrier scatters.
Kusakabe et al
The characteristic of inverted singlet-triplet excited states (iST), in which the lowest singlet excited state (S1) is lower than the lowest triplet state (T1) in energy, was observed in a dialkylamine-substituted pentaazaphenalene derivative, 5AP-N(C12)2. The transient PL measurements showed that the reverse intersystem crossing has virtually zero activation energy, whereas the intersystem crossing proceeded by a thermal activation process. T1 was located energetically above S1 with the negative energy gap between S1 and T1 (ΔEST) of −37 meV. Fluorescence and phosphorescence spectra also confirmed the negative ΔEST of −46 – −32 meV.
Lv et al
Two port feedback has been theoretically studied and proved to be effective in enhancing the degree of entanglement of the output beams for an optical four-wave mixing process, but the loss effects and phase delays need to be further concerned. Here, we use a model that is closer to practical implementation. By reasonably tuning the coefficients, we find that higher degree of entanglement and higher power of the output beams can be obtained, and the requirement for phase locking accuracy could be looser, which means this model is more promising for practical applications in quantum computation and quantum communication.
Ieiri et al
A high-power ultrasonic transducer operating on a unique principle for minimally invasive treatments is proposed, capable of treating areas inaccessible by HIFU treatments. This transducer employs two elliptical reflectors that efficiently focus ultrasound waves into a thin waveguide by utilizing mode conversion. Additionally, a slit structure is introduced to suppress wave diffraction, further enhancing the focusing capabilities of the transducer. Finite element analysis demonstrates that the proposed transducer achieves an impressive energy density magnification factor of 325, with an energy efficiency of 24.2%. This efficiency is 3.4 times higher than that of a conventional transducer, DPLUS.
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Nozomu Ishiguro et al 2024 Appl. Phys. Express 17 052006
As the first experiment at BL10U in NanoTerasu, tender X-ray ptychographic coherent diffraction imaging (PCDI) was conducted using a photon energy of 3.5 keV. The ptychographic diffraction patterns from a 200 nm thick Ta test chart and a micrometer-sized particle of sulfurized polymer were collected. Subsequently, phase images were reconstructed with resolutions of sub-20 nm and sub-50 nm, respectively. In the near future, tender X-ray PCDI with sub-10 nm resolution is anticipated to potentially revolutionize the visualization of nanoscale structures and chemical states in various functional materials composed of light elements.
Sosuke Iwamoto et al 2024 Appl. Phys. Express 17 051008
We investigated the abundance, structures, energy levels, and spin states of oxygen-related defects in 4H-SiC on the basis of first-principles calculations. We applied a hybrid functional in the overall calculations, which gives reliable defect properties, and also considered relevant defect charge states. We identified the oxygen interstitial (Oi,1), substitutional oxygen (OC), and oxygen-vacancy (OCVSi) complex as prominent defects in n-type conditions. Among them, OCVSi was predicted as a spin-1 defect with NIR emission in a previous study. On the basis of the obtained results, we discuss the possible spin decoherence sources when employing OCVSi as a spin-to-photon interface.
Nabil Ahmed et al 2024 Appl. Phys. Express
Drag between the electron-layer and the hole-layer formed in a silicon-on-insulator metal-oxide-semiconductor field-effect-transistor, with the estimated interlayer distance as small as 18 nm, is investigated. The drag resistance is measured at 10 K and mapped on the plane defined by the electron density and hole density. The analysis shows that the Coulomb drag predominates over the competing virtual-phonon drag. The observed drag resistance is as large as 103 - 104 Ω, indicating strong Coulomb interaction between the electron and hole layers.
Dan Wu et al 2024 Appl. Phys. Express 17 052007
Nonlinear optical materials, especially two-dimensional materials, are anticipated to reveal broadband optical nonlinearity for future miniaturized photonic applications. Herein, we report a physical vapor deposition method to produce β-In2Se3 thin film and investigate the broadband nonlinear absorption (β) and refraction (n2) characteristics. The β-In2Se3 semiconductor shows an excellent optical nonlinearity with large β in 102 cm GW−1 scale and n2 in 10−12 cm2 W−1 scale from visible to NIR wavelengths, which are superior to those of metal carbides and nitrides (MXenes) and metal-organic frameworks. This excellent optical nonlinearity makes β-In2Se3 a promising candidate for advanced nanophotonic devices and beyond.
Ikki Nagaoka et al 2024 Appl. Phys. Express 17 054501
This study investigates the timing margin required to handle fluctuations and variations in superconductor single-flux-quantum gate-level-pipelined adders; a smaller timing margin would improve the clock frequencies of gate-level-pipelined circuits. To evaluate timing margins, we demonstrated three 4 bit adders with 50-, 75-, and 100 GHz target clock frequencies using a 1.0 μm process. We estimated that the required timing margin of the adders was 2.1 ps. This indicates that previously reported gate-level-pipelined circuits operating at 30–60 GHz could operate at higher clock frequencies by reducing the timing margins.
Akito Ayukawa et al 2024 Appl. Phys. Express
High-quality epitaxial Mg3Sb2 thin films are promising thermoelectric materials to enable practical applications of compact and environmentally friendly thermoelectric conversion at room temperature. In this study, high-quality single-crystal Mg3Sb2 with high c-plane orientation were epitaxially grown directly on annealed c-Al2O3 substrates without passive layers. These thin films exhibited three times higher thermoelectric power factor than ever reported values due to high carrier mobility. The ultra-smooth surface of the annealed c-Al2O3 substrate facilitated the formation of high-quality Mg3Sb2 thin films without passive layers or polycrystalline interfaces that could be carrier scatters.
Gulzar Ali J et al 2024 Appl. Phys. Express 17 052005
The work examines terahertz (THz) broadband absorbers for unit topological structure (UTS) with spaced graphene. This study examined the transmission and absorption of the proposed structure without and with graphene at each dielectric interface. The UTS absorbed more light while using a cascade structure with a structural index (n) and adjusting dielectric thicknesses (Δ). Absorption increased significantly with an external magnetic field (B). The objective for a complete THz absorber is achieved with average absorption, = 0.8093 by a modified structure with n = 5, applying an external magnetic field, B = 10.7 T, Fermi level, EF = −0.48 eV, and manipulating the thickness parameter Δ.
Issei Suzuki et al 2024 Appl. Phys. Express 17 051007
We have investigated the fabrication of crystalline thin films of a liquid crystalline organic semiconductor (2-decyl-7-phenyl[1]benzothieno[3,2-b][1]benzothiophene: Ph-BTBT-10) by high-speed blade-coating at 140 mm s−1. Uniform crystalline Ph-BTBT-10 films were fabricated at temperatures over 50 °C, which is the temperature of the liquid crystal phase, without inhomogeneous recrystallization, despite the high-speed blade-coating. Transistors fabricated using these films showed a high average carrier mobility of 4.8 cm2 Vs−1 for 26 devices, with a coefficient of variation of only 7.3%. We concluded that liquid crystalline organic semiconductors are useful materials for high-speed meniscus-guided-coating for practical use.
Yu Kusakabe et al 2024 Appl. Phys. Express
The characteristic of inverted singlet-triplet excited states (iST), in which the lowest singlet excited state (S1) is lower than the lowest triplet state (T1) in energy, was observed in a dialkylamine-substituted pentaazaphenalene derivative, 5AP-N(C12)2. The transient PL measurements showed that the reverse intersystem crossing has virtually zero activation energy, whereas the intersystem crossing proceeded by a thermal activation process. T1 was located energetically above S1 with the negative energy gap between S1 and T1 (ΔEST) of −37 meV. Fluorescence and phosphorescence spectra also confirmed the negative ΔEST of −46 – −32 meV.
Lanyong Xiang et al 2024 Appl. Phys. Express 17 054002
We report a monolithic heterodyne receiver that uses the AlGaN/GaN nonlinear transmission line as a local oscillator and a mixer simultaneously. This heterodyne receiver has a high RF bandwidth from 80 to 360 GHz and a high intermediate frequency bandwidth of 18 GHz. These results indicate that this nonlinear transmission line receiver has promising potential in broadband spectrum analysis.
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Ryosuke Okumura et al 2024 Appl. Phys. Express 17 041003
Efficient reverse intersystem crossing (RISC) is an important process for thermally activated delayed fluorescence (TADF) to suppress efficiency roll-off in organic LEDs (OLEDs). Enhancing spin–orbit coupling is effective for fast RISC and is achieved by mediating a locally excited triplet state when RISC occurs between charge transfer states. Here, we experimentally confirmed that efficient RISC occurred in triarylborane-based TADF emitters named Phox-Meπ, Phox-MeOπ, and MeO3Ph-FMeπ. The three emitters showed large RISC rate constants exceeding 106 s−1. The Phox-Meπ-based OLED exhibited higher maximum external quantum efficiency (EQEmax = 10.0%) compared to the Phox-MeOπ-based OLED (EQEmax = 6.7%).
J. Koga et al 2024 Appl. Phys. Express 17 042007
Transition metal dichalcogenides with superperiodic lattice distortions have been widely investigated as the platform of ultrafast structural phase manipulations. Here we performed ultrafast electron diffraction on RT TaTe2, which exhibits a peculiar double zigzag chain pattern of Ta atoms. From the time-dependent electron diffraction pattern, we revealed a photoinduced change in the crystal structure occurring within <0.5 ps, although there is no corresponding high-temperature equilibrium phase. We further clarified the slower response (∼1.5 ps) reflecting the lattice thermalization. Our result suggests the unusual ultrafast crystal structure dynamics specific to the non-equilibrium transient process in TaTe2.
Yu Yamaguchi et al 2024 Appl. Phys. Express 17 024501
Physical reservoir computing (PRC) is useful for edge computing, although the challenge is to improve computational performance. In this study, we developed an inverted input method, the inverted input is additionally applied to a physical reservoir together with the original input, to improve the performance of the ion-gating reservoir. The error in the second-order nonlinear equation task was 7.3 × 10−5, the lowest error in reported PRC to date. Improvement of high dimensionality by the method was confirmed to be the origin of the performance enhancement. This inverted input method is versatile enough to enhance the performance of any other PRC.
Kei Maruyama et al 2024 Appl. Phys. Express 17 022004
We study the terahertz (THz) magnetic field pulse enhanced by a spiral-shaped antenna resonator (SAR). We deposit the SAR on the surface of a terbium-gallium-garnet crystal, which has a large Verdet constant, and measure the Faraday rotation angle for strong THz pulse excitation by magneto-optical sampling (MOS) with NIR light. The determined magnetic field strength and field-enhancement spectrum are consistent with the theoretical predictions. This first report of the detection of a Tesla-class picosecond magnetic field pulse by MOS is expected to be useful in research on the control of magnetization in spintronic devices.
Guo Chen et al 2024 Appl. Phys. Express 17 021001
MEMS resonant sensing devices require both HF (f) and low dissipation or high quality factor (Q) to ensure high sensitivity and high speed. In this study, we investigate the resonance properties and energy loss in the first three resonance modes, resulting in a significant increase in f‧Q product at higher orders. The third order resonance exhibits an approximately 15-fold increase in f‧Q product, while the Q factor remains nearly constant. Consequently, we achieved an ultrahigh f‧Q product exceeding 1012 Hz by higher-order resonances in single-crystal diamond cantilevers.
Dongsheng Yuan et al 2024 Appl. Phys. Express 17 015502
Ce:Li6Y(BO3)3 (LYBO) is a well-known candidate for thermal neutron detection with a very high Li concentration (3.06 × 1022/cm3). So far, as-grown crystals exhibit a milky appearance that compromises their performance as scintillators. Current work demonstrates, for the first time, the growth of scattering-free undoped and Ce-doped LYBO by a thermal quenching process. The origin and features of the scattering centers are investigated in detail. Furthermore, the annealing treatment for the scintillation activation is studied, finding that the reduction in oxygen vacancies is mandatory. Under thermal neutron irradiation, the annealed scattering-free Ce:LYBO single crystal achieves a record-high light yield of 6200 ph/n in a single decay with a lifetime as short as 24 ns.
K. Ji et al 2024 Appl. Phys. Express 17 016505
Thermal healing of focused ion beam-implanted defects in GaN is investigated by off-axis electron holography in TEM. The data reveal that healing starts at temperatures as low as about 250 °C. The healing processes result in an irreversible transition from defect-induced Fermi level pinning near the VB toward a midgap pinning induced by the crystalline-amorphous transition interface. Based on the measured pinning levels and the defect charge states, we identify the dominant defect type to be substitutional carbon on nitrogen sites.
Keiichiro Oh-ishi et al 2024 Appl. Phys. Express 17 015501
The Si-nano dot substrates formed using the ultrathin silicon oxide films were applied to fabricate CaSi2 films. The CaSi2 formed by this process was identified as the metastable phase 2H as the main component, and the 1H structure existed partially at the grains of the 2H phase. Although no experimental reports exist for the formation of 2H-CaSi2 crystal, the Si-nano dot substrates are considered as the high-entropy substrate to form the metastable phases. We experimentally determined the lattice parameter of the 2H phase by the annular dark field–scanning transmission electron microscopy observations using the Si as an internal standard sample.