Spotlights - Applied Physics Express - IOPscience

Spotlights - 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.
Spotlights
On many occasions in the past, progress in applied physics has been promoted by cross-disciplinary research and for this reason we believe that it is valuable to give readers a broad perspective on current research. Each month we will select and suggest a small number of articles with a high potential for capturing the interest of researchers in the applied physics community. We hope that Spotlights will provide opportunities to redirect readers beyond their usual interests.
Latest spotlights
Open access
Kirigami-structured flexible heat flux sensor driven by the anomalous Nernst effect
Shusaku Saito
et al
2026
Appl. Phys. Express
View article
, 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.
Open access
High-throughput, non-destructive, three-dimensional imaging of GaN threading dislocations with in-plane Burgers vector component via phase-contrast microscopy
Yukari Ishikawa
et al
2026
Appl. Phys. Express
View article
, 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.
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.
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.
Open access
High mobility In
thin films grown by atomic layer deposition using a microwave remote plasma source for field-effect transistor applications
Yuto Kawato
et al
2025
Appl. Phys. Express
18
114003
View article
, High mobility In2O3 thin films grown by atomic layer deposition using a microwave remote plasma source for field-effect transistor applications
PDF
, High mobility In2O3 thin films grown by atomic layer deposition using a microwave remote plasma source for field-effect transistor applications
In this study, we established a microwave remote plasma source (MW-RPS) to perform plasma-enhanced atomic layer deposition to grow an In
channel for FET applications. We compared MW-RPS and a conventional capacitively coupled plasma (CCP) source to investigate the effects of oxidation time in O
plasma on the physical and electrical properties of In
. Our results demonstrate that MW-RPS enables both smooth surface morphology and sufficient oxidation even with prolonged plasma exposure. The extracted intrinsic field-effect mobility of the fabricated FETs with MW-RPS-derived In
channels increased significantly with oxidation time compared to that of CCP, reaching a value of 106.2 cm
V s
−1
Open access
A multi-fin normally-off
-Ga
vertical transistor with a breakdown voltage exceeding 10 kV
Daiki Wakimoto
et al
2025
Appl. Phys. Express
18
106502
View article
, A multi-fin normally-off β-Ga2O3 vertical transistor with a breakdown voltage exceeding 10 kV
PDF
, A multi-fin normally-off β-Ga2O3 vertical transistor with a breakdown voltage exceeding 10 kV
We demonstrated a multi-fin normally-off
-Ga
vertical transistor with a breakdown voltage exceeding 10 kV, a specific on-resistance of 289 mΩ·cm
, and a power figure-of-merit of 0.35 GW cm
−2
. The vertical transistor was fabricated on a low-donor-concentration (
≈ 1.8 × 10
15
cm
−3
) and thick (thickness ≈ 85
m) epitaxial layer grown on a (011)
-Ga
substrate by halide vapor phase epitaxy to enhance the breakdown voltage. The breakdown voltage exceeding 10 kV is the highest reported for
-Ga
vertical transistors. This result indicates the great potential of Ga
vertical power devices.
Open access
Reactive species generated by cold atmospheric plasma trigger transient elevations of intracellular calcium ion and hydrogen peroxide in plant cells
Shoko Tsuboyama
et al
2025
Appl. Phys. Express
18
086001
View article
, Reactive species generated by cold atmospheric plasma trigger transient elevations of intracellular calcium ion and hydrogen peroxide in plant cells
PDF
, Reactive species generated by cold atmospheric plasma trigger transient elevations of intracellular calcium ion and hydrogen peroxide in plant cells
Cold plasma irradiation elicits various beneficial effects in plants; however, the underlying mechanisms remain poorly understood. To identify the primary triggers of plant cellular responses, we employed a real-time monitoring system to track cytosolic Ca
2+
and H
dynamics following plasma exposure, utilizing a quartz. The presence of quartz plate completely abolished the intracellular responses including transient elevations of cytosolic Ca
2+
and H
. Quantitative analyses revealed that, while the quartz transmitted electric fields and light, it effectively blocked plasma-derived reactive species. These findings suggest that reactive species are critical initiators of the initial cellular response to plasma irradiation in plants.
Open access
High Mg activation with suppressed Mg diffusion during ultra-high-pressure annealing via sequential nitrogen-ion implantation in Mg-ion-implanted GaN
Kensuke Sumida
et al
2025
Appl. Phys. Express
18
066502
View article
, High Mg activation with suppressed Mg diffusion during ultra-high-pressure annealing via sequential nitrogen-ion implantation in Mg-ion-implanted GaN
PDF
, High Mg activation with suppressed Mg diffusion during ultra-high-pressure annealing via sequential nitrogen-ion implantation in Mg-ion-implanted GaN
The Mg concentration ([Mg]), acceptor concentration (N
), and compensating donor concentration (N
) of Mg-ion implanted (Mg-I/I) and Mg+N-ion-implanted (Mg+N-I/I) GaN with various ultra-high-pressure annealing (UHPA) durations were analyzed in-depth. Sequential N-ion implantation (N-I/I) suppressed Mg diffusion after 30 min of UHPA. The net acceptor concentration of Mg+N-I/I GaN after 30 min of UHPA was more than twice that of Mg-I/I GaN. Sequential N-I/I followed by 30 min of UHPA enhances Mg substitution at Ga sites (N
/[Mg]
70%) and reduces compensating donors (N
/N
18
) while maintaining the initial Mg depth profile, thereby enabling precise Mg doping control.
Open access
Quartz-free hydride vapor phase epitaxy for production of large size GaN-on-GaN epitaxial wafers
Shota Kaneki
et al
2025
Appl. Phys. Express
18
055502
View article
, Quartz-free hydride vapor phase epitaxy for production of large size GaN-on-GaN epitaxial wafers
PDF
, Quartz-free hydride vapor phase epitaxy for production of large size GaN-on-GaN epitaxial wafers
GaN-on-GaN epitaxial growth on 4 and 6 inch wafers was demonstrated using a new mass-production-type quartz-free hydride vapor phase epitaxy (QF-HVPE) system. The thickness, effective donor density, and near-band-edge photoluminescence peak intensity were confirmed to be uniform for 4 inch wafers. In addition, a new QF-HVPE system enabled the growth of extremely pure GaN crystals with a C concentration lower than 1 × 10
14
cm
−3
, enabling a wide range of doping control from 1 × 10
14
to 1 × 10
18
cm
−3
. The resultant GaN wafers were free from C-induced mobility collapse and exhibited record-high room-temperature and maximum mobilities of 1591 cm
−1
−1
and 18,175 cm
−1
−1
at 35 K, respectively.
Open access
Ampere-class double pulse testing of half-inch H-terminated diamond MOSFET chip
Keita Takaesu
et al
2025
Appl. Phys. Express
18
036502
View article
, Ampere-class double pulse testing of half-inch H-terminated diamond MOSFET chip
PDF
, Ampere-class double pulse testing of half-inch H-terminated diamond MOSFET chip
400 metal-oxide-semiconductor field-effect transistors (MOSFETs) were fabricated on a half-inch diamond substrate. The performance of each device was evaluated, and an H-terminated diamond MOSFET chip was created by connecting over 300 of the well performing MOSFETs in parallel, resulting in a gate width of 32 cm. This chip was used for double pulse testing, with its switching characteristics being evaluated at 2.5 A. The results show a fall/rise time of 19/32 ns, respectively, and switching losses during turn-off/turn-on of 4.65/1.24 μJ. This study demonstrated switching operation at large currents in diamond power MOSFETs.
Open access
Nonvolatile magneto-thermal switching driven by vortex trapping in commercial In-Sn solder
Poonam Rani
et al
2025
Appl. Phys. Express
18
033001
View article
, Nonvolatile magneto-thermal switching driven by vortex trapping in commercial In-Sn solder
PDF
, Nonvolatile magneto-thermal switching driven by vortex trapping in commercial In-Sn solder
Magneto-thermal switching (MTS) is a key technology for efficient thermal management. Recently, large MTS with nonvolatility has been observed in Sn-Pb solders [H. Arima et al. Commun. Mater. 5, 34 (2024)] where phase separation, the different superconducting transition temperatures (
) of Sn and Pb, and magnetic-flux trapping are the causes of the nonvolatile MTS. To further understand the mechanism and to obtain the strategy for enhancing switching ratio, exploration of new phase-separated superconductors with nonvolatile MTS is needed. Here, we show that the In52-Sn48 commercial solder is a phase-separated superconducting composite with two
and traps vortices after field cooling. A clear signature of nonvolatile MTS was observed at
= 2.5 K. From specific heat analyses, we conclude that the vortices are mainly trapped in the lower-
phase (
-phase) after field cooling, which is evidence that vortex trapping also works on achieving nonvolatile MTS in phase-separated superconducting composites.
Open access
Strain-free thin film growth of vanadium dioxide deposited on 2D atomic layered material of hexagonal boron nitride investigated by their thickness dependence of insulator–metal transition behavior
Boyuan Yu
et al
2025
Appl. Phys. Express
18
025502
View article
, Strain-free thin film growth of vanadium dioxide deposited on 2D atomic layered material of hexagonal boron nitride investigated by their thickness dependence of insulator–metal transition behavior
PDF
, Strain-free thin film growth of vanadium dioxide deposited on 2D atomic layered material of hexagonal boron nitride investigated by their thickness dependence of insulator–metal transition behavior
We report on the preparation of vanadium dioxide (VO
) ultrathin films on hexagonal boron nitride (hBN), which is a typical two-dimensional material, to show clear metal–insulator transition owing to weak van der Waals interaction at their surface. It is confirmed that VO
films on hBN with thicknesses ranging from 10 to 40 nm exhibit bulk like metal–insulator transition without degradation using Raman scattering spectroscopy and electric transport measurements. These results demonstrate the importance of the 2D material nature of hBN for producing strain-free oxide thin films.
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Japanese Journal of Applied Physics