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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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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Dany Lachance-Quirion et al 2019 Appl. Phys. Express 12 070101
P. Döring and T. Tschirky 2024 Appl. Phys. Express 17 031003
In this work, degenerate n-type GaN thin films prepared by co-sputtering from a liquid Ga-target were demonstrated and their low-field scattering mechanisms are described. Extremely high donor concentrations above 3 × 1020 cm−3 at low process temperatures (<800 °C) with specific resistivities below 0.5 mΩcm were achieved. The degenerate nature of the sputtered films was verified via temperature-dependent Hall measurements (300–550 K) revealing negligible change in electron mobility and donor concentration. Scattering at ionized impurities was determined to be the major limiting factor with a minor contribution of polar optical-phonon scattering at high temperatures.
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.
Takashi Ishida et al 2024 Appl. Phys. Express 17 026501
To address the issue of the high cost of GaN substrates, a recycling process for GaN substrates using a laser slicing technique was investigated. The channel properties of lateral MOSFETs and the reverse characteristics of vertical PN diodes, which represent the main components of vertical power devices, exhibited no degradation either before and after laser slicing or due to the overall GaN substrate recycling process. This result indicates that the proposed recycling process is an effective method for reducing the cost of GaN substrates and has the potential to encourage the popularization of GaN vertical power devices.
Natsuo Taguchi et al 2024 Appl. Phys. Express 17 012002
Visible-wavelength GaN-based photonic-crystal surface-emitting lasers (PCSELs) have attracted attention for various applications, such as materials processing, high-brightness illuminations, and displays. In this letter, we demonstrate GaN-based PCSELs at green wavelengths. We formed a photonic crystal (PC) in p-GaN and filled holes of the PC with SiO2 to ensure device stability. Through a current injection test under pulsed conditions and spectral analysis, we confirmed that the fabricated device possessed Γ-point single-mode oscillation at wavelengths above 505 nm. Our results have the potential to further expand the applications of PCSELs and semiconductor lasers in visible region.
Ryoya Yamada et al 2023 Appl. Phys. Express 16 105504
This study investigated the crystallographic plane dependence of the reaction of AlN and AlGaN using heated-pressurized water under saturated vapor pressure. The results show that the reaction strongly depends on the crystallographic orientation plane, with no reaction in the +c-plane, the formation of an AlOOH-altered layer in the −c-plane, and etching in the a- and m-planes. These results suggest that the exfoliation mechanism of AlGaN grown on periodically formed AlN nanopillars on sapphire substrates using heated-pressurized water involves etching of a- and m-plane crystals, demonstrating that the proposed method is highly reproducible and versatile for large-diameter wafer exfoliation.
Advait Gilankar et al 2024 Appl. Phys. Express 17 046501
A unique field termination structure combining a three-step field plate with nitrogen ion implantation to enhance the reverse breakdown performance of Pt/β-Ga2O3 Schottky barrier diodes (SBDs) and NiO/β-Ga2O3 heterojunction diodes (HJDs) is reported. The fabricated devices showed a low Ron,sp of 6.2 mΩ cm2 for SBDs and 6.8 mΩ cm2 for HJDs. HJDs showed a 0.8 V turn-on voltage along with an ideality factor of 1.1 leading to a low effective on-resistance of 18 mΩ cm2. The devices also showed low reverse leakage current (<1 mA cm−2) and a breakdown voltage of ∼1.4 kV. These results offer an alternative, simpler route for fabricating high-performance kilovolt-class β-Ga2O3 diodes.
Takeshi Aoki et al 2024 Appl. Phys. Express 17 042004
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.
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.
Pankaj Attri et al 2024 Appl. Phys. Express 17 046001
The present study focused on CO2 capture, storage, and conversion through the innovative integration of plasma–ionic liquid (IL) technology. For the first time, we employed plasma-IL technology to confront climate change challenges. We utilized 1-Butyl-3-methylimidazolium chloride IL to capture and store CO2 under atmospheric pressure, and subsequently employed plasma to induce the transformation of IL-captured CO2 into CO. Furthermore, we performed computer simulations to enhance our understanding of the CO2 and CO capture processes of water and IL solutions. This comprehensive approach provides valuable insights into the potential of plasma–IL technology as a viable solution for climate change.
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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.
Nobuhisa Ishii and Ryuji Itakura 2024 Appl. Phys. Express 17 042006
We demonstrate the generation of sub-two-cycle intense laser pulses based on two-stage hollow-core fiber (HCF) compression in a compact setup (footprint of 0.65 m × 2.85 m) using a commercial Yb:KGW regenerative amplifier. Spectrally broadened laser pulses with an output power of 7.2 W from the second HCF stage are compressed down to 6.6 fs (1.9 cycles at 1030 nm) using a pair of chirp mirrors and a pair of wedges with an efficiency of 86%, leading to a compressed output of 6.2 W. A pulse-to-pulse energy stability of 0.17% is measured for 10 min.
Yui Takahashi et al 2024 Appl. Phys. Express 17 041002
We report on the control of carrier density in r-SnO2 thin films grown on isostructural r-TiO2 substrates by doping with Sb aiming for power-electronics applications. The carrier density was tuned within a range of 3 × 1016–2 × 1019 cm−3. Two types of donors with different activation energies, attributed to Sb at Sn sites and oxygen vacancies, are present in the thin films. Both activation energies decrease as the concentration of Sb increases. A vertical Schottky barrier diode employing a Sb:r-SnO2/Nb:r-TiO2 exhibits a clear rectifying property with a rectification ratio of 103 at ±1 V.
Jiulong Yu et al 2024 Appl. Phys. Express 17 045501
In this paper, single-crystal GePb films were obtained by magnetron sputtering with high substrate temperature and rapid deposition rate. The GePb films have high crystalline qualities and smooth surface. The Pb content reached 1.29% and no segregation was observed. Based on this, a GePb based p–i–n photodetector was successfully prepared. The device showed a RT dark current density of 5.83 mA cm−2 at −1.0 V and a cutoff wavelength of 1990 nm, which covers all communication windows. At the wavelength of 1625 nm, responsivity of the photodetector reached 0.132 A W−1 at −1.0 V. The device demonstrates potential application in optical communications.
Junia Nomura et al 2024 Appl. Phys. Express 17 042005
We demonstrate a master oscillator power amplifier system that emits single-frequency, high-energy optical pulses at 1539 nm using an Er, Yb:glass planar waveguide amplifier with a normalized frequency of the waveguide of 4.4. A maximum pulse energy of 9.7 mJ is observed at a repetition frequency of 500 Hz. The signal to noise ratio is 25 dB and is independent of the repetition frequency from 100 to 500 Hz. The beam quality factor M2 of the output is 1.03 thanks to the small normalized frequency of the planar waveguide.
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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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Kaneko et al
Stochastic magnetic tunnel junctions (s-MTJs) attract 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 〈R〉 of s-MTJs with perpendicular magnetization as functions of perpendicular magnetic fields Hz and temperatures T=20-130°C. We observe that both relaxation time (time-domain response) and the slope of the 〈R〉-Hz 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.
Inoue et al
Sinusoidal electric fields are applied to liquid crystals (LCs) across various frequencies ranging from 0.1 Hz to 10 kHz to investigate the oscillatory behavior of LC directors. In a 1.5-μm-thick 5CB cell, a significant decline in refractive index change occurs in the frequency range greater than 10 Hz, in which the LC director cannot sufficiently follow the rapid fluctuations in field intensity. To evaluate the response speed of the LC under sinusoidal electric fields, the cutoff frequency is introduced as a response indicator. Enhancement to the cutoff frequency can be achieved through conventional fast response techniques such as polymer-stabilized LCs.
Nonogaki et al
We demonstrate a method for fast and precise Brillouin frequency shift measurement based on searching for the zero-crossing point of a virtually composed spectra of Brillouin gain and loss, obtained by dual-frequency probe beam. Simulations and experiments show that searching for the zero-crossing point of virtually synthesized Brillouin gain spectrum can be easily done without a large error compared with the peak search of Brillouin gain spectrum in the conventional method.
Fukamachi et al
We have developed the GaN-based distributed feedback laser diode (DFB-LD) with the detuning of +5 nm to obtain smaller temperature dependence of the threshold current. We found that the current-light characteristics almost overlapped up to 300 mW between 25○C and 80○C. The estimated characteristic temperature is about 2550 K. These indicate that our DFB-LD is promising for applications that require small temperature dependence in the output power and oscillation wavelength at constant operation current without precise temperature control.
Wang et al
Improved p-GaN gate reliability is achieved through a simple oxygen compensation technique (OCT), which involves oxygen plasma treatment after gate opening and subsequential wet etching. The OCT compensates for the Mg acceptors near the p-GaN surface, leading to an extended depletion region under the same gate bias and thus reducing the electric field. Furthermore, the Schottky barrier height also increases by OCT. Consequently, suppressed gate leakage current and enlarged gate breakdown voltage are achieved. Notably, the maximum applicable gate bias also increases from 4 V to 8.1 V for a 10-year lifetime at a failure rate of 1%.
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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.
Nobuhisa Ishii and Ryuji Itakura 2024 Appl. Phys. Express 17 042006
We demonstrate the generation of sub-two-cycle intense laser pulses based on two-stage hollow-core fiber (HCF) compression in a compact setup (footprint of 0.65 m × 2.85 m) using a commercial Yb:KGW regenerative amplifier. Spectrally broadened laser pulses with an output power of 7.2 W from the second HCF stage are compressed down to 6.6 fs (1.9 cycles at 1030 nm) using a pair of chirp mirrors and a pair of wedges with an efficiency of 86%, leading to a compressed output of 6.2 W. A pulse-to-pulse energy stability of 0.17% is measured for 10 min.
Yui Takahashi et al 2024 Appl. Phys. Express 17 041002
We report on the control of carrier density in r-SnO2 thin films grown on isostructural r-TiO2 substrates by doping with Sb aiming for power-electronics applications. The carrier density was tuned within a range of 3 × 1016–2 × 1019 cm−3. Two types of donors with different activation energies, attributed to Sb at Sn sites and oxygen vacancies, are present in the thin films. Both activation energies decrease as the concentration of Sb increases. A vertical Schottky barrier diode employing a Sb:r-SnO2/Nb:r-TiO2 exhibits a clear rectifying property with a rectification ratio of 103 at ±1 V.
Jiulong Yu et al 2024 Appl. Phys. Express 17 045501
In this paper, single-crystal GePb films were obtained by magnetron sputtering with high substrate temperature and rapid deposition rate. The GePb films have high crystalline qualities and smooth surface. The Pb content reached 1.29% and no segregation was observed. Based on this, a GePb based p–i–n photodetector was successfully prepared. The device showed a RT dark current density of 5.83 mA cm−2 at −1.0 V and a cutoff wavelength of 1990 nm, which covers all communication windows. At the wavelength of 1625 nm, responsivity of the photodetector reached 0.132 A W−1 at −1.0 V. The device demonstrates potential application in optical communications.
Haruna Kaneko et al 2024 Appl. Phys. Express
Stochastic magnetic tunnel junctions (s-MTJs) attract 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 〈R〉 of s-MTJs with perpendicular magnetization as functions of perpendicular magnetic fields Hz and temperatures T=20-130°C. We observe that both relaxation time (time-domain response) and the slope of the 〈R〉-Hz 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.
Yo Inoue et al 2024 Appl. Phys. Express
Sinusoidal electric fields are applied to liquid crystals (LCs) across various frequencies ranging from 0.1 Hz to 10 kHz to investigate the oscillatory behavior of LC directors. In a 1.5-μm-thick 5CB cell, a significant decline in refractive index change occurs in the frequency range greater than 10 Hz, in which the LC director cannot sufficiently follow the rapid fluctuations in field intensity. To evaluate the response speed of the LC under sinusoidal electric fields, the cutoff frequency is introduced as a response indicator. Enhancement to the cutoff frequency can be achieved through conventional fast response techniques such as polymer-stabilized LCs.
Hayato Nonogaki et al 2024 Appl. Phys. Express
We demonstrate a method for fast and precise Brillouin frequency shift measurement based on searching for the zero-crossing point of a virtually composed spectra of Brillouin gain and loss, obtained by dual-frequency probe beam. Simulations and experiments show that searching for the zero-crossing point of virtually synthesized Brillouin gain spectrum can be easily done without a large error compared with the peak search of Brillouin gain spectrum in the conventional method.
Toshihiko Fukamachi et al 2024 Appl. Phys. Express
We have developed the GaN-based distributed feedback laser diode (DFB-LD) with the detuning of +5 nm to obtain smaller temperature dependence of the threshold current. We found that the current-light characteristics almost overlapped up to 300 mW between 25○C and 80○C. The estimated characteristic temperature is about 2550 K. These indicate that our DFB-LD is promising for applications that require small temperature dependence in the output power and oscillation wavelength at constant operation current without precise temperature control.
Junia Nomura et al 2024 Appl. Phys. Express 17 042005
We demonstrate a master oscillator power amplifier system that emits single-frequency, high-energy optical pulses at 1539 nm using an Er, Yb:glass planar waveguide amplifier with a normalized frequency of the waveguide of 4.4. A maximum pulse energy of 9.7 mJ is observed at a repetition frequency of 500 Hz. The signal to noise ratio is 25 dB and is independent of the repetition frequency from 100 to 500 Hz. The beam quality factor M2 of the output is 1.03 thanks to the small normalized frequency of the planar waveguide.
Takeshi Aoki et al 2024 Appl. Phys. Express 17 042004
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.
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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.