Applied Physics Express - IOPscience

Applied Physics Express - IOPscience
Applied Physics Express
The Japan Society of Applied Physics
The Japan Society of Applied Physics (JSAP) serves as an academic interface between science and engineering and an interactive platform for academia and the industry. JSAP is a "conduit" for the transfer of fundamental concepts to the industry for development and technological applications.
JSAP was established as an official academic society in 1946, and since then, it has been one of the leading academic societies in Japan. The society's interests cover a broad variety of scientific and technological fields, and JSAP continues to explore state-of-the-art and interdisciplinary topics.
To this end, the JSAP holds annual conferences; publishes scientific journals; actively sponsors events, symposia, and festivals related to science education; and compiles information related to state-of-the-art technology for the public.
OPEN ACCESS
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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Median submission to first decision before peer review
4 days
Median submission to first decision after peer review
13 days
Impact factor
2.2
Citescore
4.7
The following article is
Open access
High-density two-dimensional electron gas in ScAlN/GaN heterostructures grown by sputter epitaxy with enhanced metal supply
Tomoya Okuda
et al
2026
Appl. Phys. Express
19
041001
View article
, High-density two-dimensional electron gas in ScAlN/GaN heterostructures grown by sputter epitaxy with enhanced metal supply
PDF
, High-density two-dimensional electron gas in ScAlN/GaN heterostructures grown by sputter epitaxy with enhanced metal supply
We report high-density two-dimensional electron gases in ScAlN/AlGaN/AlN/GaN heterostructures grown by sputter epitaxy with an enhanced metal supply. By optimizing the growth temperature to 775 °C, we achieved atomically flat surfaces and high crystallinity. Moreover, we obtained a record-high sheet carrier density (
) of 2.24 × 10
13
cm
−2
for the sputtered ScAlN films, which is comparable to the values achieved using metal–organic chemical vapor deposition and molecular beam epitaxy. Temperature-dependent Hall effect measurements and scattering analysis using Matthiessen’s rule revealed that the high carrier density enhances interface roughness scattering, which becomes the dominant mobility-limiting mechanism at low temperatures. These results demonstrate that sputter epitaxy with an increased metal-to-nitrogen flux ratio enables high-density polarization-induced 2DEGs and provides a competitive approach for realizing high-performance ScAlN/GaN HEMT heterostructures.
The following article is
Open access
Freestanding 30 mm square {111} twin-free heteroepitaxial diamonds grown on highly-misoriented {0001} sapphire substrates
Seong-Woo Kim
et al
2026
Appl. Phys. Express
19
031003
View article
, Freestanding 30 mm square {111} twin-free heteroepitaxial diamonds grown on highly-misoriented {0001} sapphire substrates
PDF
, Freestanding 30 mm square {111} twin-free heteroepitaxial diamonds grown on highly-misoriented {0001} sapphire substrates
Freestanding 30 mm square twin-free {111} diamond films were obtained by heteroepitaxial growth on highly misoriented sapphire substrates. X-ray rocking curve revealed high crystal quality of the diamond with full width at half maximum of 94 arcsec for {111} plane. X-ray pole figure of {220} diffraction peaks exhibited threefold symmetry, suggesting the single crystallinity without twinning. Results of systematic investigation of off-angle and off-direction dependencies demonstrated that large misorientation toward 〈11-20〉 of {0001} plane sapphire substrate not only promotes step-flow growth but also suppresses twin formation by aligning 〈11-2〉 step direction of {111} diamond.
The following article is
Open access
AlScN/GaN HEMTs with 4 A/mm on-current and maximum oscillation frequency >130 GHz
Kazuki Nomoto
et al
2025
Appl. Phys. Express
18
016506
View article
, AlScN/GaN HEMTs with 4 A/mm on-current and maximum oscillation frequency >130 GHz
PDF
, AlScN/GaN HEMTs with 4 A/mm on-current and maximum oscillation frequency >130 GHz
Aluminum Scandium Nitride (AlScN) is an attractive material for use as a lattice-matched epitaxial barrier layer in GaN high-electron mobility transistors (HEMTs). Here we report the device fabrication, direct current (DC) and radio frequency (RF) characteristics of epitaxial AlScN/AlN/GaN HEMTs on SiC substrates with regrown ohmic contacts. These devices show record high on-current of over 4 A/mm, high cutoff frequency (
) of 92.4 GHz and maximum oscillation frequency (
) of 134.3 GHz.
The following article is
Open access
Prospects for
-Ga
: now and into the future
Kohei Sasaki 2024
Appl. Phys. Express
17
090101
View article
, Prospects for β-Ga2O3: now and into the future
PDF
, Prospects for β-Ga2O3: now and into the future
This review describes the progress of research on gallium oxide as a material for power devices, covering the development of bulk crystal growth through to epitaxial growth, defect evaluations, device processes, and development, all based on the author’s research experiences. During the last decade or so, the epi-wafer size has been expanded to 4–6 inches, and Schottky barrier diodes and field-effect transistors capable of ampere-class operations and with breakdown voltages of several kV have been demonstrated. On the other hand, challenges to the practical application of gallium oxide power devices, such as the cost of epi-wafers, killer defects, purity of epitaxial layer, etc., have also become apparent. This paper provides a comprehensive summary of the history of these developments, including not only papers but also patents and conference presentations, and gives my personal views on the prospects for this material’s continued development.
The following article is
Open access
Development of GaN trench MOSFET process technologies
Tetsu Kachi 2026
Appl. Phys. Express
19
010103
View article
, Development of GaN trench MOSFET process technologies
PDF
, Development of GaN trench MOSFET process technologies
GaN holds great promise as a next-generation power device material. While lateral GaN power devices have already been commercialized and are finding expanding applications, vertical GaN power devices remain at the developmental stage. This paper systematically describes the fabrication process technologies for vertical GaN trench MOSFETs that we have developed over many years. The established elemental technologies include low-doped epitaxial growth, precise trench-shape control, etching-damage removal, p-type ion implantation, formation of high-concentration n-type sputtered layers, and high-quality AlSiO gate dielectrics. Highly reliable and reproducible process technologies are indispensable for the practical realization of vertical GaN power devices. Moreover, the technologies developed in this study are broadly applicable to various vertical GaN device architectures. Consequently, the set of elemental process technologies established here constitutes a fundamental process platform and is expected to play a crucial role in enabling the future practical application of vertical GaN power electronics.
The following article is
Open access
Kinetics of thermal oxidation of silicon
Takanobu Watanabe 2025
Appl. Phys. Express
18
120101
View article
, Kinetics of thermal oxidation of silicon
PDF
, Kinetics of thermal oxidation of silicon
This article reviews findings from the 2000s that led to a reevaluation of the conventional understanding of silicon thermal oxidation, prompted by the discovery of the so-called layer-by-layer oxidation phenomenon in the 1990s. Since the seminal work of Deal and Grove, silicon thermal oxidation has been described by a two-step model: an initial linear regime limited by interfacial reactions, followed by a parabolic regime governed by the diffusion of oxidant molecules. In 2003, however, it was demonstrated that layer-by-layer oxidation could be reproduced by a simple diffusion-limited process. Moreover, first-principles calculations have revealed that the energy barrier for interfacial oxidation with O
molecules is negligible. These findings underscore the need to revise the conventional Deal-Grove model, particularly in the context of dry oxidation. In this article, a linear-parabolic equation, similar to the Deal–Grove equation, is derived by assuming an increase in the diffusion barrier of oxidant molecules within a compressively stressed SiO
region, known as the structural transition region, near the interface. The proposed model not only reshapes the interpretation of the linear-parabolic growth behavior but also calls for a reconsideration of the anomalously rapid initial growth observed in dry oxidation. Portions of this article are adapted from a Japanese publication (T. Watanabe, Kinetics of Silicon Oxidation, to be published in
Thermal Oxidation of Si, SiC and Related Semiconductors
, Chapter 10, The Japan Society of Applied Physics, Kindai-kagakusha Co., Ltd., (2026) [in Japanese]).
The following article is
Open access
A critical review of Mg
Sb
-based thermoelectric materials
Hezhang Li
et al
2026
Appl. Phys. Express
19
020101
View article
, A critical review of Mg3Sb2-based thermoelectric materials
PDF
, A critical review of Mg3Sb2-based thermoelectric materials
Mg
Sb
-based materials have emerged as highly promising
-type thermoelectric materials within the medium temperature range (300–800 K), offering a more cost-effective and environmentally benign alternative to conventional telluride-based thermoelectric materials. These materials complement Bi
Te
-based systems for near-room temperature applications (300–500 K) and PbTe/GeTe/SnTe for medium-temperature ranges (500–800 K). This paper presents a systematic review of recent significant advances in the thermoelectric performance of Mg
Sb
, achieved through optimized doping and fabrication strategies. It outlines key methodologies and underlying physical mechanisms that contribute to high-performance
-type Mg
Sb
, discusses challenges associated with device integration, and proposes future research directions.
The following article is
Open access
Quantum geometry and
-wave magnets with
X = p, d, f, g, i
Motohiko Ezawa 2026
Appl. Phys. Express
19
030101
View article
, Quantum geometry and X-wave magnets with X = p, d, f, g, i
PDF
, Quantum geometry and X-wave magnets with X = p, d, f, g, i
Quantum geometry is a differential geometry based on quantum mechanics. It is related to various transport and optical properties in condensed matter physics. The Zeeman quantum geometry is a generalization of quantum geometry including the spin degrees of freedom. It is related to electromagnetic cross-responses. Quantum geometry is generalized to non-Hermitian systems and density matrices. In particular, the latter is quantum information geometry, where the quantum Fisher information naturally arises as a quantum metric. We apply these results to the
-wave magnets, which include
-wave,
-wave and
-wave altermagnets as well as
-wave and
-wave magnets. They have universal physics for anomalous Hall conductivity, tunneling magneto-resistance and planar Hall effects. We also study magneto-optical conductivity, magnetic circular dichroism and Friedel oscillations in the
-wave magnets. Various analytic formulas are derived in the case of two-band Hamiltonians. This paper presents a review of the recent progress together with some original results.
The following article is
Open access
Recent advances in the physics of Dirac plasmons in graphene and related 2D materials and their THz device applications
Taiichi Otsuji
et al
2026
Appl. Phys. Express
19
020103
View article
, Recent advances in the physics of Dirac plasmons in graphene and related 2D materials and their THz device applications
PDF
, Recent advances in the physics of Dirac plasmons in graphene and related 2D materials and their THz device applications
The terahertz (THz) frequency range (0.1–10 THz) bridges the electronic and photonic spectral domains and offers key opportunities for high-speed communication, sensing, and spectroscopy. However, the realization of compact, coherent, and room-temperature THz sources and detectors remains still a long-standing challenge. Recent advances in two-dimensional (2D) materials, hosting graphene-like massless Dirac fermions, have opened some new paths toward overcoming this limitation. This paper reviews recent advances in the physics of Dirac plasmons in graphene and related 2D heterostructure materials and their THz device applications. It first outlines the fundamentals of 2D plasmon hydrodynamics, nonlinearities, and current-driven instabilities, including Dyakonov–Shur Ryzhii–Satou–Shur, and Cherenkov-type mechanisms. A new mechanism, Coulomb drag instability, recently discovered by the authors, is theoretically shown to provide the largest plasmonic gain among these mechanisms, offering a new route to efficient THz amplification and lasing. Its experimental verification is currently in progress. The review also discusses graphene-based plasmonic lasers, amplifiers, and detectors, and recent developments in graphene/black-arsenic–phosphorus heterostructures that enable band-structure and plasmonic engineering. Finally, topological-insulator-based heterostructures are introduced as promising material systems. These advances demonstrate that Dirac plasmon physics provides a robust foundation for next-generation THz device technology.
The following article is
Open access
GaN-based MIS HEMT with SiAlN gate dielectric achieving over 70% PAE and 10 W mm
−1
at 8 GHz
Yuichi Minoura
et al
2026
Appl. Phys. Express
19
021010
View article
, GaN-based MIS HEMT with SiAlN gate dielectric achieving over 70% PAE and 10 W mm−1 at 8 GHz
PDF
, GaN-based MIS HEMT with SiAlN gate dielectric achieving over 70% PAE and 10 W mm−1 at 8 GHz
We achieved a simultaneous record-high power-added efficiency (PAE) of 71.4% and an output power density of 10.4 W mm
−1
at 8 GHz in an AlGaN/GaN metal-insulator-semiconductor (MIS) high-electron-mobility transistor (HEMT) on a free-standing GaN substrate, utilizing SiAlN as the gate dielectric. This exceptional performance stems from the high quality of the metal-organic chemical vapor deposited SiAlN gate dielectric and the gate field plate structure employing a SiN/SiAlN stack, enabling the combined realization of high output power and efficiency. These results emphatically demonstrate the significant potential of MIS gate structures for advanced microwave power amplifiers across various applications.
The following article is
Open access
Laser frequency stabilization using a spatially multiplexed microfabricated Rb vapor cell
Seji Kang
et al
2026
Appl. Phys. Express
19
042003
View article
, Laser frequency stabilization using a spatially multiplexed microfabricated Rb vapor cell
PDF
, Laser frequency stabilization using a spatially multiplexed microfabricated Rb vapor cell
We demonstrate a laser stabilization based on a spatially-multiplexed, microfabricated rubidium vapor cell. This design integrates multiple optical apertures within a cell, enabling a single input beam to simultaneously capture both Doppler-broadened and saturated absorption spectroscopy signals while a dedicated non-absorbing aperture directs the beam toward the physics package. We achieve a frequency stability of 4 × 10
−13
at 100 s, and partial correction of the Doppler background allows the system to remain stable at the 10
−12
-level up to 10
s. This architecture significantly reduces optical complexity while providing a robust, high-performance laser source for deployable quantum sensors.
The following article is
Open access
Overview and future perspective of Si tandem solar cells
Masafumi Yamaguchi
et al
2026
Appl. Phys. Express
19
040105
View article
, Overview and future perspective of Si tandem solar cells
PDF
, Overview and future perspective of Si tandem solar cells
Silicon solar cells are the most established solar cell technology and are expected to dominate the market also in the near future. As state-of-the-art silicon solar cells are approaching the Shockley–Queisser limit (32%–33%), stacking silicon solar cells with other photovoltaic materials to form multi-junction devices is a promising pathway to raise the efficiency. However, many challenges stand in the way of fully realizing the potential of Si tandem solar cells because heterogeneously integrating silicon with other materials often degrades their qualities. Recently, promising efficiencies of 35% and 36.1% have been demonstrated for perovskite/Si 2-junction and III–V/Si 3-junction tandem solar cells, respectively. However, further efficiency improvements and cost reduction of the Si tandem solar cell modules are necessary if they are to compete with Si single-junction solar cell modules. Motivated by the potential, but also by the remaining open questions, this paper presents an overview of recent research endeavors and challenges in the field of Si tandem solar cells. The first part of this review focuses on the integration of silicon with III–V compound semiconductor, perovskites and other materials to form multi-junction solar cells. The second part presents perspectives for Si-based tandem solar cells and modules. Finally, the paper presents an analytical model to compare the material qualities of different types of Si-based tandem solar cells and project the practical efficiency limits, which are found to be more than 39% and 44% for 2-junction and 3-junction Si-based tandem solar cells, respectively. In this paper, cost and reliability issues for Si tandem cells and modules are discussed.
The following article is
Open access
Quantum sensing and imaging in the MeV regime of nuclear medicine
Kenji Shimazoe and Mizuki Uenomachi 2026
Appl. Phys. Express
19
040104
View article
, Quantum sensing and imaging in the MeV regime of nuclear medicine
PDF
, Quantum sensing and imaging in the MeV regime of nuclear medicine
This paper reviews approaches to improving imaging capabilities in nuclear medicine using quantum-inspired technologies. Positron emission tomography and single-photon emission computed tomography are established diagnostic methods in nuclear medicine and are extremely useful for detecting early stage cancers and other diseases through the detection of small numbers of molecules using sub-MeV gamma rays; however, the principles of these modalities have not changed for more than five decades. Recently, quantum technologies have attracted significant attention, particularly quantum sensors and quantum entanglement in the optical-photon regime. In this review, we introduce emerging efforts that utilize quantum-inspired technologies, such as electron spin, nuclear spin and quantum entanglement in the MeV photon (gamma ray) regime. Quantum-enhanced imaging in nuclear medicine may directly contribute to improvements in diagnostic capability and patients’ quality of life.
The following article is
Open access
Next-generation light-emitting devices combining organic emitters and halide perovskites
Toshinori Matsushima 2026
Appl. Phys. Express
19
040103
View article
, Next-generation light-emitting devices combining organic emitters and halide perovskites
PDF
, Next-generation light-emitting devices combining organic emitters and halide perovskites
Organic-perovskite hybrid light-emitting devices combine the superior emissive properties of organic fluorophores with the high carrier mobility and structural versatility of halide perovskites. This review summarizes recent advances in hybrid architectures where perovskites function as transport layers, host matrices, or structurally integrated frameworks for organic emitters. Such designs enable low-voltage operation, scalable device thickness, and improved operational stability. Particular focus is placed on energy-transfer-based emission systems, where excitons are generated in the inorganic perovskite framework and transferred to organic fluorophores, enabling exciton utilization beyond the 25% singlet limit. Fluorophore-containing two-dimensional perovskites with vertically oriented inorganic layers are also discussed.
The following article is
Open access
Monolithic bidirectional 2DHG diamond switch
Sora Kawai
et al
2026
Appl. Phys. Express
19
041002
View article
, Monolithic bidirectional 2DHG diamond switch
PDF
, Monolithic bidirectional 2DHG diamond switch
This work presents a monolithic bidirectional two-dimensional hole gas (2DHG) diamond switch capable of bidirectional blocking operation for the first time. All essential operation modes unique to bidirectional switches were demonstrated. The
on
was estimated to be 8.2 mΩ cm
, and the bidirectional breakdown voltage reaches 290 V. Consequently, the bidirectional 2DHG diamond switch achieves an
on
less than one-tenth of that of the deep-depletion-type switch while maintaining higher breakdown voltage. These results suggest that monolithic bidirectional 2DHG diamond switches are promising candidates for on-board chargers employing matrix converters or three-level T-type converters.
The following article is
Open access
Overview and future perspective of Si tandem solar cells
Masafumi Yamaguchi
et al
2026
Appl. Phys. Express
19
040105
View article
, Overview and future perspective of Si tandem solar cells
PDF
, Overview and future perspective of Si tandem solar cells
Silicon solar cells are the most established solar cell technology and are expected to dominate the market also in the near future. As state-of-the-art silicon solar cells are approaching the Shockley–Queisser limit (32%–33%), stacking silicon solar cells with other photovoltaic materials to form multi-junction devices is a promising pathway to raise the efficiency. However, many challenges stand in the way of fully realizing the potential of Si tandem solar cells because heterogeneously integrating silicon with other materials often degrades their qualities. Recently, promising efficiencies of 35% and 36.1% have been demonstrated for perovskite/Si 2-junction and III–V/Si 3-junction tandem solar cells, respectively. However, further efficiency improvements and cost reduction of the Si tandem solar cell modules are necessary if they are to compete with Si single-junction solar cell modules. Motivated by the potential, but also by the remaining open questions, this paper presents an overview of recent research endeavors and challenges in the field of Si tandem solar cells. The first part of this review focuses on the integration of silicon with III–V compound semiconductor, perovskites and other materials to form multi-junction solar cells. The second part presents perspectives for Si-based tandem solar cells and modules. Finally, the paper presents an analytical model to compare the material qualities of different types of Si-based tandem solar cells and project the practical efficiency limits, which are found to be more than 39% and 44% for 2-junction and 3-junction Si-based tandem solar cells, respectively. In this paper, cost and reliability issues for Si tandem cells and modules are discussed.
The following article is
Open access
Quantum sensing and imaging in the MeV regime of nuclear medicine
Kenji Shimazoe and Mizuki Uenomachi 2026
Appl. Phys. Express
19
040104
View article
, Quantum sensing and imaging in the MeV regime of nuclear medicine
PDF
, Quantum sensing and imaging in the MeV regime of nuclear medicine
This paper reviews approaches to improving imaging capabilities in nuclear medicine using quantum-inspired technologies. Positron emission tomography and single-photon emission computed tomography are established diagnostic methods in nuclear medicine and are extremely useful for detecting early stage cancers and other diseases through the detection of small numbers of molecules using sub-MeV gamma rays; however, the principles of these modalities have not changed for more than five decades. Recently, quantum technologies have attracted significant attention, particularly quantum sensors and quantum entanglement in the optical-photon regime. In this review, we introduce emerging efforts that utilize quantum-inspired technologies, such as electron spin, nuclear spin and quantum entanglement in the MeV photon (gamma ray) regime. Quantum-enhanced imaging in nuclear medicine may directly contribute to improvements in diagnostic capability and patients’ quality of life.
The following article is
Open access
Next-generation light-emitting devices combining organic emitters and halide perovskites
Toshinori Matsushima 2026
Appl. Phys. Express
19
040103
View article
, Next-generation light-emitting devices combining organic emitters and halide perovskites
PDF
, Next-generation light-emitting devices combining organic emitters and halide perovskites
Organic-perovskite hybrid light-emitting devices combine the superior emissive properties of organic fluorophores with the high carrier mobility and structural versatility of halide perovskites. This review summarizes recent advances in hybrid architectures where perovskites function as transport layers, host matrices, or structurally integrated frameworks for organic emitters. Such designs enable low-voltage operation, scalable device thickness, and improved operational stability. Particular focus is placed on energy-transfer-based emission systems, where excitons are generated in the inorganic perovskite framework and transferred to organic fluorophores, enabling exciton utilization beyond the 25% singlet limit. Fluorophore-containing two-dimensional perovskites with vertically oriented inorganic layers are also discussed.
The following article is
Open access
Emerging trends in non-contact ultrasonic sensing with electromagnetic acoustic transducers
Hirotsugu Ogi 2026
Appl. Phys. Express
19
040102
View article
, Emerging trends in non-contact ultrasonic sensing with electromagnetic acoustic transducers
PDF
, Emerging trends in non-contact ultrasonic sensing with electromagnetic acoustic transducers
Electromagnetic acoustic transducers (EMATs) have long been recognized as powerful tools for non-contact non-destructive evaluation of materials. This review first revisits the fundamental physical principles of EMAT operation and summarizes representative EMAT configurations that have been developed for various ultrasonic modes. Although the practical adoption of EMATs has traditionally been constrained by low electromechanical energy-conversion efficiency, recent advances in digital electronics have significantly reduced power consumption and system size, reshaping the EMAT landscape. Furthermore, recent studies using point-focusing EMATs are highlighted, demonstrating enhanced capabilities for subwavelength defect detection and localized nonlinear ultrasonic measurements. These developments have paved the way for portable and field-deployable EMAT systems, and position EMATs as key components in next-generation ultrasonic sensing and non-destructive testing technologies.
The following article is
Open access
Electric-field-induced magnetization reversal in cobalt-substituted BiFeO
: a review
Kei Shigematsu and Masaki Azuma 2026
Appl. Phys. Express
19
040101
View article
, Electric-field-induced magnetization reversal in cobalt-substituted BiFeO3: a review
PDF
, Electric-field-induced magnetization reversal in cobalt-substituted BiFeO3: a review
Electric-field control in multiferroic materials is attracting attention for next-generation memory devices with low power consumption, high recording density, and non-volatility. This review overviews magnetization reversal in cobalt-substituted BiFeO
(BiFe
1–
Co
), a single-phase room-temperature multiferroic. Experimental results from microscopic direct observations of domains using scanning probe microscopy are summarized, highlighting how electric-field-induced reversal is influenced by domain structures, film orientations, and switching angles. Spatial control of domains in nanodot arrays and associated size effects are also discussed. These insights offer a clear perspective toward magnetoelectric memory applications.
The following article is
Open access
Kirigami-structured flexible heat flux sensor driven by the anomalous Nernst effect
Saito et al
View accepted manuscript
, Kirigami-structured flexible heat flux sensor driven by the anomalous Nernst effect
PDF
, Kirigami-structured flexible heat flux sensor driven by the anomalous Nernst effect
This letter proposes and demonstrates a flexible architecture for an anomalous-Nernst-effect -based heat flux sensor inspired by kirigami, a traditional Japanese paper-cutting art. A prototype device comprises an amorphous Sm19Co81 film and Ta/Au electrode on a flexible substrate pre-patterned with a periodic-cutting kirigami structure. The estimated heat flux sensitivity of the kirigami-structured sensor was comparable to that of a conventional sensor without kirigami structure and remained unchanged even when it was stretched by 10%. Our approach opens a pathway toward versatile and mechanically compliant heat flux sensing that is applicable to various surfaces.
The following article is
Open access
Biochemical pathways for device nanoarchitectonics: organic semiconductors interfaced with biomolecular systems
Ohashi et al
View accepted manuscript
, Biochemical pathways for device nanoarchitectonics: organic semiconductors interfaced with biomolecular systems
PDF
, Biochemical pathways for device nanoarchitectonics: organic semiconductors interfaced with biomolecular systems
This review discusses organic semiconductors interfaced with biomolecular systems, focusing on the construction of material systems through biochemical pathways for device nanoarchitectonics. The initial section highlights biosensors as representative applications at the interface of device engineering and biosystem science. The subsequent sections describe nanoarchitectonics approaches for the synthesis and organization of organic semiconductor devices using bioprocessing. In particular, doping of organic semiconductors in water under ambient conditions coupled with bioprocessing are emphasized, including proton-coupled electron transfer (PCET) and sugar redox reactions. Inspired by the sophisticated molecular architectures that enables ultra-high-level functions in biological systems, nanoarchitectonics is expected to facilitate further advances in organic semiconductor biodevices.
The following article is
Open access
High-throughput, non-destructive, three-dimensional imaging of GaN threading dislocations with in-plane Burgers vector component via phase-contrast microscopy
Ishikawa et al
View accepted manuscript
, High-throughput, non-destructive, three-dimensional imaging of GaN threading dislocations with in-plane Burgers vector component via phase-contrast microscopy
PDF
, High-throughput, non-destructive, three-dimensional imaging of GaN threading dislocations with in-plane Burgers vector component via phase-contrast microscopy
We demonstrate a nondestructive, high-throughput method for imaging dislocations in GaN (0001) using phase-contrast microscopy (PCM). A one-to-one correspondence between threading dislocation contrasts in PCM and multiphoton excitation photoluminescence images confirms that PCM enables detection of dislocations with in-plane Burgers vector components. The contrast morphology reflects dislocation inclination: vertical dislocations appear as dots, whereas inclined dislocations appear as lines. By shifting the focal plane from top to back surface, the three-dimensional propagation paths of dislocations can be traced. Dislocations separated by 1.3 μm are resolved. PCM also reveals scratches, subsurface scratches, facet boundaries, and voids.
The following article is
Open access
Enhanced four-wave mixing in graphene-integrated silicon slot waveguides
Wang et al
View accepted manuscript
, Enhanced four-wave mixing in graphene-integrated silicon slot waveguides
PDF
, Enhanced four-wave mixing in graphene-integrated silicon slot waveguides
Leveraging graphene’s giant third-order nonlinearity and ultrafast response, we experimentally demonstrate a graphene-integrated slot waveguide designed to maximize the effective light-matter interaction. Through four-wave mixing (FWM) experiments, we achieved a conversion efficiency of −29.1 dB in a slot waveguide covered with an optimized graphene-light interaction length of 60 μm, outperforming the strip waveguide structures by approximately 18.4 dB. This device not only provides pathways for realizing high-speed and low-power all-optical signal processing, but also lays a sound theoretical and experimental foundation for the design and integration of highly nonlinear silicon photonic devices.
Trending on Altmetric
The following article is
Open access
Demonstration of GaN optical power converter with 60% power conversion efficiency
Hisashi Ogawa
et al
2026
Appl. Phys. Express
19
021009
View article
, Demonstration of GaN optical power converter with 60% power conversion efficiency
PDF
, Demonstration of GaN optical power converter with 60% power conversion efficiency
We demonstrate a GaN optical power converter (OPC) achieving a power conversion efficiency of 60.2% under monochromatic light illumination at 401 nm. The device maintains high performance under a high illumination intensity of 96 W cm
−2
and at a high temperature of 125 °C. These results highlight GaN OPCs as a viable platform for a variety of applications, including optical wireless power transfer, power-over-fiber links, and electrically isolated power delivery.
The following article is
Open access
Design principles for optimizing pyroelectric responses of doped HfO
Jian Liu 2026
Appl. Phys. Express
19
021005
View article
, Design principles for optimizing pyroelectric responses of doped HfO2
PDF
, Design principles for optimizing pyroelectric responses of doped HfO2
Ferroelectric HfO
is an emerging pyroelectric material with promising energy-harvesting applications. Herein, via ab-initio molecular dynamics simulations, we investigate the role of dopants in tailoring the pyroelectricity in ferroelectric HfO
. We demonstrate that dopant perturbs the local bonding environment of host HfO
structure, giving rise to notable pyroelectricity. The pyroelectric response is further enhanced at the ferroelectric-to-paraelectric phase transition, characterized by a Curie temperature that reduces with increasing doping concentrations. The reduction is more pronounced for dopants with ionic radii smaller than the host. The present work highlights the efficient tuning of pyroelectric response in ferroelectric HfO
by doping.
More Spotlight Articles
The following article is
Open access
Hybrid quantum systems based on magnonics
Dany Lachance-Quirion
et al
2019
Appl. Phys. Express
12
070101
View article
, Hybrid quantum systems based on magnonics
PDF
, Hybrid quantum systems based on magnonics
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.
Development of X-ray-induced afterglow characterization system
Takayuki Yanagida
et al
2014
Appl. Phys. Express
062401
View article
, Development of X-ray-induced afterglow characterization system
PDF
, Development of X-ray-induced afterglow characterization system
To evaluate the X-ray-induced afterglow phenomenon, we developed an ionizing-radiation-induced luminescence characterization system equipped with a pulse-width-tunable X-ray source. The system consists of a pulse X-ray tube and a detector system based on photon counting. The excitation pulse width was tunable from nano- to millisecond ranges, and the dynamic range of the X-ray-induced afterglow was 10
. Conventional scintillators for X-ray CT or security systems, namely, Bi
Ge
12
, CdWO
, Tl-doped CsI, and Tb and Pr-codoped Gd
S, were evaluated for the performance test. Results show that the afterglow time profiles of these scintillators are consistent with generally known results with high accuracy.
Defect engineering in SiC technology for high-voltage power devices
Tsunenobu Kimoto and Heiji Watanabe 2020
Appl. Phys. Express
13
120101
View article
, Defect engineering in SiC technology for high-voltage power devices
PDF
, Defect engineering in SiC technology for high-voltage power devices
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.
The following article is
Open access
Prospects for
-Ga
: now and into the future
Kohei Sasaki 2024
Appl. Phys. Express
17
090101
View article
, Prospects for β-Ga2O3: now and into the future
PDF
, Prospects for β-Ga2O3: now and into the future
This review describes the progress of research on gallium oxide as a material for power devices, covering the development of bulk crystal growth through to epitaxial growth, defect evaluations, device processes, and development, all based on the author’s research experiences. During the last decade or so, the epi-wafer size has been expanded to 4–6 inches, and Schottky barrier diodes and field-effect transistors capable of ampere-class operations and with breakdown voltages of several kV have been demonstrated. On the other hand, challenges to the practical application of gallium oxide power devices, such as the cost of epi-wafers, killer defects, purity of epitaxial layer, etc., have also become apparent. This paper provides a comprehensive summary of the history of these developments, including not only papers but also patents and conference presentations, and gives my personal views on the prospects for this material’s continued development.
Device-Quality β-Ga
Epitaxial Films Fabricated by Ozone Molecular Beam Epitaxy
Kohei Sasaki
et al
2012
Appl. Phys. Express
035502
View article
, Device-Quality β-Ga2O3 Epitaxial Films Fabricated by Ozone Molecular Beam Epitaxy
PDF
, Device-Quality β-Ga2O3 Epitaxial Films Fabricated by Ozone Molecular Beam Epitaxy
N-type Ga
homoepitaxial thick films were grown on β-Ga
(010) substrates by ozone molecular beam epitaxy. The epitaxial growth rate was increased by more than ten times by changing from the (100) plane to the (010) plane. The carrier concentration of the epitaxial layers could be varied within the range of 10
16
–10
19
cm
-3
by changing the Sn doping concentration. Platinum Schottky barrier diodes (SBDs) on 1.4-µm-thick β-Ga
homoepitaxial layers were demonstrated for the first time. The SBDs exhibited a reverse breakdown voltage of 100 V, an on-resistance of 2 mΩ cm
, and a forward voltage of 1.7 V (at 200 A/cm
).
Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency
Takayoshi Takano
et al
2017
Appl. Phys. Express
10
031002
View article
, Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency
PDF
, Deep-ultraviolet light-emitting diodes with external quantum efficiency higher than 20% at 275 nm achieved by improving light-extraction efficiency
Enhancing the light-extraction efficiency is the key issue for realizing highly efficient AlGaN-based ultraviolet light-emitting diodes (UV-LEDs). We introduced several features to improve the light extraction: a transparent AlGaN:Mg contact layer, a Rh mirror electrode, an AlN template on a patterned sapphire substrate, and encapsulation resin. The combination of the AlGaN:Mg contact layer and the Rh mirror electrode significantly improved the output power and the external quantum efficiency (EQE) of UV-LEDs. By introducing the aforementioned features, a maximum EQE of >20% at an emission wavelength of 275 nm and a 20-mA direct current was achieved.
Size-independent peak efficiency of III-nitride micro-light-emitting-diodes using chemical treatment and sidewall passivation
Matthew S. Wong
et al
2019
Appl. Phys. Express
12
097004
View article
, Size-independent peak efficiency of III-nitride micro-light-emitting-diodes using chemical treatment and sidewall passivation
PDF
, Size-independent peak efficiency of III-nitride micro-light-emitting-diodes using chemical treatment and sidewall passivation
Micro-light-emitting-diodes (
LEDs) with size-independent peak external quantum efficiency behavior was demonstrated from 10 × 10
to 100 × 100
by employing a combination of chemical treatment and atomic-layer deposition (ALD) sidewall passivation. The chemical treatment and sidewall passivation improved the ideality factors of
LEDs from 3.4 to 2.5. The results from the combination of chemical treatment and ALD sidewall passivation suggest the issue of size dependent efficiency can be resolved with proper sidewall treatments after dry etching.
A 271.8 nm deep-ultraviolet laser diode for room temperature operation
Ziyi Zhang
et al
2019
Appl. Phys. Express
12
124003
View article
, A 271.8 nm deep-ultraviolet laser diode for room temperature operation
PDF
, A 271.8 nm deep-ultraviolet laser diode for room temperature operation
We present a deep-ultraviolet semiconductor laser diode that operates under current injection at room temperature and at a very short wavelength. The laser structure was grown on the (0001) face of a single-crystal aluminum nitride substrate. The measured lasing wavelength was 271.8 nm with a pulsed duration of 50 ns and a repetition frequency of 2 kHz. A polarization-induced doping cladding layer was employed to achieve hole conductivity and injection without intentional impurity doping. Even with this undoped layer, we were still able to achieve a low operation voltage of 13.8 V at a lasing threshold current of 0.4 A.
All-oxide p–n heterojunction diodes comprising p-type NiO and n-type β-Ga
Yoshihiro Kokubun
et al
2016
Appl. Phys. Express
091101
View article
, All-oxide p–n heterojunction diodes comprising p-type NiO and n-type β-Ga2O3
PDF
, All-oxide p–n heterojunction diodes comprising p-type NiO and n-type β-Ga2O3
NiO/β-Ga
all-oxide p–n heterojunction diodes were fabricated for the first time using p-type NiO epitaxial layers grown on n-type β-Ga
substrates. The fabricated diodes exhibited good rectifying current–voltage characteristics, with a rectifying ratio greater than 10
at ±3 V. The capacitance–voltage measurements showed that the built-in voltage was 1.4 V. These results were discussed in terms of the energy band diagram of a type-II heterojunction, where the conduction band and valence band discontinuities were estimated to be 2.2 and 3.4 eV, respectively.
The following article is
Open access
Indication of current-injection lasing from an organic semiconductor
Atula S. D. Sandanayaka
et al
2019
Appl. Phys. Express
12
061010
View article
, Indication of current-injection lasing from an organic semiconductor
PDF
, Indication of current-injection lasing from an organic semiconductor
In this study, we investigate the lasing properties of 4,4′-bis[(
-carbazole)styryl]biphenyl thin films under electrical pumping. The electroluminescent devices incorporate a mixed-order distributed feedback SiO
grating into an organic light-emitting diode structure and emit blue lasing. The results provide an indication of lasing by direct injection of current into an organic thin film through selection of a high-gain organic semiconductor showing clear separation of the lasing wavelength from significant triplet and polaron absorption and design of a proper feedback structure with low losses at high current densities. This study represents an important advance toward a future organic laser diode technology.
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Japanese Journal of Applied Physics
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2008-present
Applied Physics Express
Online ISSN: 1882-0786
Print ISSN: 1882-0778