The 100 most-cited articles in Applied Physics Letters, 2023

A composite gradient-index metasurface (C-GM) array for microwave power reception (MPR) operating at 5.8 GHz center frequency was introduced. The array is insensitive to the polarization of incident plane waves and possesses cosine gradient modulation characteristics, which can convert the incident plane waves into surface waves focused at the center of the array. The focused surface wave energy is then collected by an omnidirectional antenna and fed back to a single rectifier for radio frequency (RF) to direct current (DC) conversion, resulting in DC output. Simulation results show that the array can fully excite surface waves under different polarized plane wave excitations, and the omnidirectional antenna has good matching characteristics with the array, achieving an energy collection efficiency of 66.52%. The array was fabricated and measured, achieving an energy reception efficiency of 59.91% and an RF-DC conversion efficiency of 34.83%, which is consistent with the simulation results. The proposed C-GM array can capture higher electromagnetic power by simply increasing its…

You May Be Interested InHigh-order mode bulk acoustic wave resonators based on polarity-inverted SiAlN/AlN multilayered films for high-frequency operation

We demonstrate tunnel magnetoresistance (TMR) ratios of up to 631% at room temperature (RT) using CoFe/MgO/CoFe(001) epitaxial magnetic tunnel junctions (MTJs). The TMR ratio increased up to 1143% at 10 K. The large TMR ratios resulted from fine-tuning of atomic-scale structures of the MTJs, such as crystallographic orientations and MgO interface oxidation by interface insertion of ultrathin CoFe and Mg layers, which are expected to enhance the well-known Δ1 coherent tunneling transport. Interestingly, the TMR oscillation effect, which is not covered by the standard coherent tunneling theory, also became significant. A 0.32-nm period TMR oscillation with increasing MgO thickness dominates the transport in a wide range of MgO thicknesses; the peak-to-valley difference of the TMR oscillation exceeds 140% at RT, which is attributed to the appearance of large oscillatory components in the resistance area product.

Room temperature operation of terahertz quantum cascade lasers (THz QCLs) has been a long-pursued goal to realize compact semiconductor THz sources. In this paper, we report on improving the maximum operating temperature of THz QCLs to ∼ 261 K as a step toward the realization of this goal.

Altermagnetism can achieve spin-split bands in collinear symmetry-compensated antiferromagnets. Here, we predict altermagnetic order in Janus monolayer Cr2SO with eliminated inversion symmetry, which can realize the combination of piezoelectricity and altermagnetism in a two-dimensional (2D) material, namely, 2D piezoelectric altermagnetism. It is found that Cr2SO is an altermagnetic semiconductor, and the spin-split bands of both valence and conduction bands are near the Fermi level. The Cr2SO has large out-of-plane piezoelectricity (|d31| = 0.97 pm/V), which is highly desirable for ultrathin piezoelectric device application. Due to spin-valley locking, both spin and valley can be polarized by simply breaking the corresponding crystal symmetry with uniaxial strain. Our findings provide a platform to integrate spin, piezoelectricity, and valley in a single material, which is useful for multi-functional device applications.

In the past two decades, the research on acoustic metamaterials has flourished, which is also benefited from the development of additive manufacturing technology. The exotic physical phenomena and principles exhibited by acoustic metamaterials have attracted widespread attention from academia and engineering communities, which can be applied to noise reduction and acoustic nondestructive testing in industrial; invisible cloaking and camouflage in the military; medical ultrasound imaging in national health; acoustic stealth in defense security, detection in the ocean, communication, and other fields, i.e., acoustic metamaterials have important scientific research value and broad application prospects. This review summarizes the history and research status of acoustic metamaterials, focusing on the main research progress of metamaterials in nonlinear acoustic and acoustic coatings fields, including the research on acoustic coatings with cavities of our group. Finally, the future development direction of acoustic metamaterials is prospected, and the difficulties and challenges faced by…

In this paper, a differential quartz-enhanced photoacoustic spectroscopy (D-QEPAS) sensor is reported. The differential photoacoustic cell (PAC) was used to generate the photoacoustic effect. Two quartz tuning forks (QTFs) with a quality factor (Q) up to 10 000 were used as the acoustic wave transducers. The signal of D-QEPAS sensor was doubly enhanced by the differential characteristic of differential PAC and resonant response of QTF. The background noise was suppressed based on the differential principle. With the help of the finite element method, the acoustic field characteristics were simulated and calculated. Wavelength modulation spectroscopy technique and second harmonic (2f) detection technique were applied to detect photoacoustic signal. Trace acetylene (C2H2) gas detection was performed to verify the D-QEPAS sensor performance. The 2f signal amplitude of differential mode was 116.03 μV, which had a 1.65 times improvement compared with the 2f signal amplitudes of QTF1. When the integration time was 334 s, the minimum detection limit of D-QEPAS sensor was about 496.7 ppb.…

We report a vertical β-Ga2O3 Schottky barrier diode (SBD) with BaTiO3 as field plate oxide on a low doped thick epitaxial layer exhibiting 2.1 kV breakdown voltage. A thick drift layer of 11 μm with a low effective doping concentration of 8 × 1015 cm–3 is used to achieve high breakdown voltage. Using the high-k dielectric with a dielectric constant of 248, the breakdown voltage increases from 816 V for the non-field-plated SBD to 2152 V (>2× improvement) for the field-plated SBD without compromising the on-state performance. The diode dimensions are varied to analyze the effect of edge high-field related leakage with reverse bias and also the effect of current spreading during forward operation. Very uniform distribution of breakdown voltages of 2152 ± 20 V are observed for the diode diameters from 50 to 300 μm for the field-plated SBDs. The on and off state power losses are also analyzed and compared with the non-field-plated devices and the switching losses are estimated analytically.

We report on the thickness scaling behavior of ferroelectric Sc0.3Al0.7N (ScAlN) films grown on Mo substrates by molecular beam epitaxy. Switchable ferroelectricity is confirmed in ScAlN films with thicknesses ranging from 100 to 5 nm. An increase in coercive field and a significant diminution of remnant polarization are found when the ferroelectric layer is scaled down to below 20 nm. Notably, a switching voltage of 2–3.8 V and saturated remnant polarization of ∼23 μC/cm2 are measured in 5 nm thick ScAlN. X-ray diffractions and transmission electron microscopy studies indicate that the increase in coercive field and diminishment in switchable polarization can be closely linked to the surface oxidation and strain state in ultrathin ScAlN films. This work sheds light on the fundamental thickness scaling fingerprints of ScAlN thin films and represents an important step for next-generation compact and power-efficient devices and applications based on nitride ferroelectrics.

Future applications for emerging AlN semiconductor electronics and optoelectronics are facilitated by emerging doping technologies enabled by low temperature, non-equilibrium epitaxy. Defect and impurity compensation can be reduced by controlling the surface chemistry with reducing compensating vacancy concentrations being a key driver for lower temperature growth. Contrary to common understanding, low temperature, metal-rich vacuum processes are shown to have higher diffusion lengths than high temperature nitrogen-rich methods. This feature can be utilized to inhibit silicon-DX center formation without compromises in crystal quality. First principles calculations identify the valence split-off band as the dominant hole band contributing to impurity band formation (as opposed to the heavy and light hole bands in other nitrides). This anomalous band structure causes an impurity band to form at dopant concentrations similar to GaN even though AlN has a deeper isolated acceptor energy and results in hole mobilities that are substantially higher than possible in GaN. AlN hole…

Laser cavity-solitons can appear in systems comprised of a nonlinear microcavity nested within an amplifying fiber loop. These states are robust and self-emergent and constitute an attractive class of solitons that are highly suitable for microcomb generation. Here, we present a detailed study of the free-running stability properties of the carrier frequency and repetition rate of single solitons, which are the most suitable states for developing robust ultrafast and high repetition rate comb sources. We achieve free-running fractional stability on both optical carrier and repetition rate (i.e., 48.9 GHz) frequencies on the order of 10−9 for a 1 s gate time. The repetition rate results compare well with the performance of state-of-the-art (externally driven) microcomb sources, and the carrier frequency stability is in the range of performance typical of modern free-running fiber lasers. Finally, we show that these quantities can be controlled by modulating the laser pump current and the cavity length, providing a path for active locking and long-term stabilization.

In this work, we numerically and experimentally investigate topological rainbow trapping and energy amplification of acoustic waves in a gradient phononic crystal (PC) structure. Thanks to the acoustic valley Hall effect, topological interface states (TISs) are generated along the interface between two PCs with different topological phases. To achieve rainbow trapping, we introduce the gradient into a 3D-printed PC structure by varying the geometrical parameter of scatterers along the interface. The incident acoustic waves at different frequencies split, stop, and, hence, are significantly amplified at different positions. Notably, the rainbow trapping of TISs is immune to random structural disorders. The topological rainbow trapping is promising for the design of broadband energy harvesters with excellent robustness.

With the rapid development of intelligent wearable electronic devices, highly compressible porous piezoresistive sensors are in imperative demand. However, the robustness of conductive coating that affects the stability and durability of porous piezoresistive sensors still needs to be solved urgently. In this work, a flexible conductive MXene/PEDOT:PSS@Melamine foam (MPMF) piezoresistive sensor was designed and prepared by simply dip-coating it in MXene and PEDOT:PSS mixed solution. Here, foam skeleton was first treated with PDA to improve its hydrophilicity and enhance the interfacial interaction with the functional groups of MXene nanosheets. More importantly, the usage of PEDOT:PSS can fix the MXene nanosheets tightly and construct synergistic conductive network between them, obtaining stable, robust, and highly conductive coating. Based on the contact effect between the adjacent conductive skeleton, the prepared MPMF sensor displays excellent piezoresistive sensing performances, which includes a wide working range (up to 80% compression strain, 60 kPa pressure), high sensitivity…

In this Letter, we demonstrated fully epitaxial ScAlN/AlGaN/GaN based ferroelectric high electron mobility transistors (HEMTs). Clean and atomically sharp heterostructure interfaces were obtained by utilizing molecular beam epitaxy. The fabricated ferroelectric gate HEMTs showed counterclockwise hysteretic transfer curves with a wide threshold voltage tuning range of 3.8 V, a large ON/OFF ratio of 3 × 107, and reconfigurable output characteristics depending on the poling conditions. The high quality ferroelectric gate stack and effective ferroelectric polarization coupling lead to improved subthreshold performance, with subthreshold swing values approaching 110 and 30 mV/dec under forward and backward gate sweeps, respectively. The results provide fundamental insight into the ferroelectric polarization coupling and threshold tuning processes in ferroelectric nitride heterostructures and are promising for nitride-based nonvolatile, multi-functional, reconfigurable power, and radio frequency devices as well as memory devices and negative capacitance transistors for next-generation…

In this work, we present theoretical predictions of a two-dimensional collinear antiferromagnetic semimetal, CrO, which exhibits a giant spin-split band structure, spin-momentum locked transport properties, and a high Néel temperature. Specifically, CrO features two pairs of spin-polarized anisotropic Weyl points at the Fermi level. By manipulating the position of these Weyl points with strain, we demonstrate that four different antiferromagnetic spintronic states with zero net magnetic moments can be achieved, including semimetals with two spin-polarized transport channels, half-semimetals, semiconductors with two spin-polarized transport channels, and half-semiconductors. The strain-induced semiconducting state also preserves the ultra-high carrier mobility of Weyl points, and the bandgap can be easily tuned. These findings offer a good avenue in spintronics without net magnetic moment or strong spin–orbit coupling and could lead to the development of antiferromagnetic materials for spintronic applications.

The recent review [Phys. Rev. Appl. 18, 027001 (2022)] has considered that the existing schemes of nonreciprocal radiation are greatly limited by the narrow-operated bandwidth and small angular range. To address these key challenges, here, the wide-angle and broadband nonreciprocal radiation based on cascaded dielectric and Weyl semimetal (WS) grating atop a thick continuous metal film is investigated. It is shown that strong nonreciprocal radiation with nonreciprocity larger than 0.9 is achieved in the spectral range of 14.77–16.175 μm for the angle of 59°. The physical origin behind this broadband nonreciprocal radiation is revealed through investigating the magnetic field distributions at several selected wavelengths and is also confirmed by the impedance matching theory. In addition, the broadband nonreciprocal radiation performance remains stably in a wide parameter space. Furthermore, it is found that the broadband spectral nonreciprocity can be maintained well in a wide angular range, in particular, above 0.7 nonreciprocity can be realized in the wavelength range of 14.5–16.5…

In this Letter, we report on the phase-controlled topological plasmons in 1D graphene nanoribbons (GNRs) based on a Su−Schrieffer−Heeger (SSH) model variant. By considering the dipole–dipole mode interactions, we first study the normal SSH model by an effective Hamiltonian and calculate the Zak phase as a topological invariant, finding that it is nontrivial (trivial) when the coupling distance is bigger (smaller) than half the period. Then, we reveal that the edge modes with fields highly localized at only one side exist in the model with nontrivial topology and shows the robustness of strong field confinement and extreme frequency stability against in-plane and out-of-plane disorders. Finally, we introduce the offset SSH model variant by vertically offsetting one of the GNR in SSH unit, which allows us to greatly engineer both the width of topological gap and the number of topological windows. The underlying physics are uncovered by defining a parameter called phase difference, which reveals that the topological edge modes appear (disappear) generally near the positions where the…

On-chip terahertz (THz) biosensors have enormous potential in advancing the development of integrable devices for real-time, label-free, and noninvasive detection of proteins, DNA, and cancerous tissue. However, high absorption of THz waves by water necessitates evanescent field-based biosensing. The conventional on-chip THz biosensors with small mode confinement volumes and scaling sensitivity to defects severely limit the interaction of analyte with the electromagnetic field. Here, we reveal a topological waveguide cavity system with topologically protected propagating interfacial modes, exhibiting evanescent waves with an out-of-plane field extent of 0.3λ0, where λ0 is the wavelength corresponding to the cavity resonance frequency. Our experiments involving biomolecule detection and leaf-hydration monitoring show that the near-field of high-Q topological cavity resonances accurately detects minute frequency shifts over extended periods, facilitating real-time sensing and monitoring of biological matter. Implementation of topologically protected evanescent fields in…

We report the demonstration of ferroelectric switching in yttrium (Y)-doped nitride semiconductors. In this study, single-crystalline, wurtzite Y0.07Al0.93N films were epitaxially grown on GaN/sapphire templates by plasma-assisted molecular beam epitaxy. The ferroelectric switching process has been investigated by current density–electric field (J-E) and polarization–electric field (P-E) loops as well as positive-up-negative-down measurements, showing a coercive field of ∼6 MV/cm and a switchable polarization of ∼130 μC/cm2. Ferroelectric switching was further confirmed via butterfly shape capacitance–voltage (C-V) loops and polarity-sensitive wet etching. The realization of ferroelectric, Y-doped AlN films further extends the family of nitride ferroelectrics and unravels a wealth of intriguing opportunities in III-nitride based electronic, piezo-electronic, and optoelectronic devices.

Significant efforts are being put into the development of efficient micrometer-scale light emitting diodes (LEDs) for future display technologies due to their marked benefits over existing displays. To date, however, the efficiency of microLED devices remains significantly lower than that of conventional broad-area devices. The deterioration in device performance with smaller device size has been linked to the plasma damage induced on mesa sidewalls during device fabrication. Here, we studied bottom-up red-emitting nanowire LEDs with different Mg doping levels in the p-GaN layer. The resulting sub-micron LED devices show a distinct improvement in efficiency with increasing Mg dopant incorporation. Through optimization of the doping, we measured an external quantum efficiency of ∼8.3% and a wall-plug efficiency of ∼4.6%, at a current density of ∼1 A/cm2, for a red-emitting sub-micrometer scale LED operating at >630 nm. This study highlights the importance of p-doping in microLEDs for attaining high efficiency performance in nanostructure-based devices.

Neural networks have revolutionized the area of artificial intelligence and introduced transformative applications to almost every scientific field and industry. However, this success comes at a great price; the energy requirements for training advanced models are unsustainable. One promising way to address this pressing issue is by developing low-energy neuromorphic hardware that directly supports the algorithm's requirements. The intrinsic non-volatility, non-linearity, and memory of spintronic devices make them appealing candidates for neuromorphic devices. Here, we focus on the reservoir computing paradigm, a recurrent network with a simple training algorithm suitable for computation with spintronic devices since they can provide the properties of non-linearity and memory. We review technologies and methods for developing neuromorphic spintronic devices and conclude with critical open issues to address before such devices become widely used.

We achieved continuous-wave 8.3-dB squeezed light generation using a terahertz-order-broadband waveguide optical parametric amplifier by improving a measurement setup from our previous work [T. Kashiwazaki et al., Appl. Phys. Lett. 119, 251104 (2021)], where a low-loss periodically poled lithium niobate (PPLN) waveguide had shown 6.3-dB squeezing at a 6 THz frequency. First, to improve efficiency of the squeezed light detection, we reduced effective optical loss to about 12% by removing extra optics and changing the detection method into a low-loss balanced homodyne measurement. Second, to minimize phase-locking fluctuation, we constructed a frequency-optimized phase-locking system by comprehending its frequency responses. Finally, we found optimal experimental parameters of a measurement frequency and a pump power from their dependences for the squeezing levels. The measurement frequency was decided as 11 MHz to maximize a clearance between shot and circuit noises. Furthermore, pump power was optimized as 660 mW to get higher squeezing level while suppressing anti-squeezed-noise…

This Letter reports a high performance β-Ga2O3 thin channel MOSFET with T gate and degenerately doped (n++) source/drain contacts regrown by metal organic chemical vapor deposition. Highly scaled T-gate with a gate length of 160–200 nm was fabricated to achieve enhanced RF performance and passivated with 200 nm silicon nitride. Peak drain current (ID,MAX) of 285 mA/mm and peak transconductance (gm) of 52 mS/mm were measured at 10 V drain bias with 23.5 Ω mm on resistance (RON). Metal/n++ contact resistance of 0.078 Ω mm was extracted from transfer length measurements. RON is possibly dominated by interface resistance between channel and highly doped n++ regrown layer. A gate-to-drain breakdown voltage of 192 V is measured for LGD = 355 nm resulting in average breakdown field (EAVG) of 5.4 MV/cm. This EAVG is the highest reported among all sub-micron gate length lateral FETs. Current gain cut off frequency (fT) of 11 GHz and record power gain cut off frequency (fMAX) of approximately 48 GHz were extracted from small signal measurements. fT is limited by DC-RF dispersion due to…

Photonic spin Hall effect (PSHE) is an effective metrological tool to characterize the variation in weak refractive index (RI) and nanostructure parameters. In this Letter, a highly sensitive terahertz Janus sensor (JS) based on PSHE is proposed. Through the asymmetric arrangement of different dielectrics, the sensor has a Janus feature, realizing the multitasking of thickness and RI detection on multiple scales. When electromagnetic waves (EWs) are incident into the JS from the forward scale, the number of graphene layers (1–7 layers) can be exactly identified by thickness detection. Enhancing the PSHE by the property of graphene, the JS can extend the thickness change of the graphene layer at the nanometer level by 106 times to the millimeter level with a sensitivity of 3.02 × 10−3 m/nm. In the case of EWs backward scale propagation, based on the sensitivity of 6.244 × 10−3 m/RIU, the JS can identify different kinds of waterborne bacterium such as Vibrio cholerae, Escherichia coli, and Shigella flexneri, in the RI range of 1.355–1.43 with high precision. The design of the…

Ferroelectric Al1−xScxN has raised much interest in recent years due to its unique ferroelectric properties and complementary metal oxide semiconductor back-end-of-line compatible processing temperatures. Potential applications in embedded nonvolatile memory, however, require ferroelectric materials to switch at relatively low voltages. One approach to achieving a lower switching voltage is to significantly reduce the Al1−xScxN thickness. In this work, ferroelectric behavior in 5–27 nm films of sputter deposited Al0.72Sc0.28N has been studied. We find that the 10 kHz normalized coercive field increases from 4.4 to 7.3 MV/cm when reducing the film thickness from 27.1 to 5.4 nm, while over the same thickness range, the characteristic breakdown field of a 12.5 μm radius capacitor increases from 8.3 to 12.1 MV/cm. The 5.4 nm film demonstrates ferroelectric switching at 5.5 V when excited with a 500 ns pulse and a switching speed of 60 ns.

Ferroelectric materials have been explored for a long time for easy integration with state-of-the-art semiconductor technologies. Doped wurtzite nitrides have been reported as promising candidates due to their high stability, compatibility, and scalability. We investigate doping effects on ferroelectric properties of Sc-doped AlN (AlScN) and B-doped AlN (AlBN) by first-principles methods. The energy barrier against polarization switching is observed to decrease with increasing doping concentration at low concentration ranges, which is the origin of the emerging ferroelectricity in doped AlN. Further increasing the doping concentration to a critical value, the ferroelectric wurtzite phase transforms into paraelectric phases (a rock salt phase for AlScN and a zinc blende phase for AlBN), making it invalid to decrease the coercivity by increasing the doping concentration. Furthermore, it is revealed that different nonpolar structures (a hexagonal phase for AlScN and a β-BeO phase for AlBN) appear in the ferroelectric switching pathway, generating different switching features in doped…

A device for electromagnetic energy absorption and conversion was investigated as an electromagnetic energy harvester, which is based on a four-ring multi-resistance unit. The device can convert microwave energy to thermal energy and then to electrical energy through the Bi2Te3 thermoelectric material adhered to the load resistance. The energy harvesting efficiency, power loss distribution, and current density distribution of the harvester were analyzed. In addition, the energy harvesting efficiency of the unit under different incident angles and polarization angles was studied, and the effect of incident power on the temperature and energy conversion efficiency of the unit was analyzed. The simulation results showed that the energy harvesting efficiency of the harvester reaches 99.5% at 5.8 GHz. Each unit in the harvester can generate an output voltage of 171.8 mV under 7 W incident wave power, and the maximum output power is 9.71 mW. To verify the effectiveness of this method, a 5 × 5 unit array model was fabricated and measured, and the measurement results were consistent with…

Optical metasurfaces have recently emerged as the game changer in light manipulation and opened up new perspectives in many subfields of optics and photonics. Recent developments in nonlocal metasurfaces, in which the nanoscale building blocks respond to the incoming light collectively rather than as individual objects, are especially promising for enhancing and controlling the nonlinear optical phenomena. In this article, we provide a brief overview of the basic principles of nonlocal metasurfaces in the context of their nonlinear optical functionalities. We discuss the origin and the regimes of the nonlocal response, covering the aspects of multiple scattering, radiation damping, quality factor, local-field enhancement, and temporal dynamics. Some important aspects are illustrated by computational examples. We also give our personal viewpoint on the selected ideas and research directions in nonlocal and nonlinear metasurfaces, including the role of spatial symmetry in nonlocal interactions, the effects of phase and momentum matching in frequency conversion, as well as the…

An accurate knowledge of lattice parameters of ScxAl1−xN is essential for understanding the elastic and piezoelectric properties of this compound as well as for the ability to engineer its strain state in heterostructures. Using high-resolution x-ray diffractometry, we determine the lattice parameters of 100-nm-thick undoped ScxAl1−xN layers grown on GaN(0001) templates by plasma-assisted molecular beam epitaxy. The Sc content x of the layers is measured independently by both x-ray photoelectron spectroscopy and energy-dispersive x-ray spectroscopy, and it ranges from 0 to 0.25. The in-plane lattice parameter of the layers linearly increases with increasing x, while their out-of-plane lattice parameter remains constant. Layers with x≈0.09 are found to be lattice matched to GaN, resulting in a smooth surface and a structural perfection equivalent to that of the GaN underlayer. In addition, a two-dimensional electron gas is induced at the ScxAl1−xN/GaN heterointerface, with the highest sheet electron density and mobility observed for lattice-matched conditions.

In this work, a solar-blind UV photodetector array is fabricated and discussed, based on a metalorganic chemical vapor deposition-grown β-Ga2O3 thin film, toward optical communication application. The high-performance photodetector unit shows a significant photo-to-dark current ratio of 3.4 × 105, a high responsivity of 61.3 A/W, an external quantum efficiency of 3 × 104%, a specific detectivity of 5.2 × 1014 Jones, and a fast response time of 35 ms. In addition, a solar-blind UV/visible light rejection ratio of 2.43 × 102 is achieved, suggesting decent spectral selectivity. For the array, the maximum photocurrent standard deviation is below 12% for every group with a similar layout arrangement. Furthermore, the dark current is at picoampere level, leading to low background noise for the optical communication system. Taking the 50% photocurrent value as the readout threshold line to avoid interference from the exterior meanwhile retaining about 500 on/off cycles, the optical communicated result shows effective outputting information “NJUPT2023” coming from a total of 256 “1” and “0”…

The fast development of the fifth-generation (5G) wireless systems and substantial growth of data usage have imposed stringent requirements for high-frequency and wideband radio frequency devices. Here, it is reported on a longitudinal leaky surface acoustic wave (LLSAW) mode acoustic resonator with a large electromechanical coupling factor (kt2), high operating frequency, and efficient spurious suppression. Through systematical finite element method simulations, available design spaces such as supporting substrate, propagation angle, and lithium niobate (LN) thickness have been fully investigated with the aim of stimulating the intended LLSAW and suppressing spurious modes concurrently. Optimization results reveal that the LLSAW mode wave propagating in X-35°Y LN/SiC piezoelectric-on-insulator (POI) bilayer structure possesses a large kt2 without significant interference from other spurious modes. To verify the theoretical analyses, LLSAW resonators were fabricated and exhibited a near spurious-free response with the operating frequency over 6 GHz, and kt2 as large as 22.7%. This…

Polypropylene is considered to be the material of choice for environmentally friendly high voltage direct current cable insulation. The high power transmission of electrical energy exposes insulating materials to high temperatures and electric fields, resulting in the degradation of material properties. This paper reports that organic molecular semiconductors with strong electron affinity can effectively modulate electrical properties of polypropylene. The charge injection and transport process are analyzed by considering a combination of relations describing various conduction models in dielectrics, including the Richardson–Schottky (RS) emission and the hopping conduction. Based on the performed experiments, a modified Wiesmann–Zeller (WZ) model is proposed to simulate the electrical treeing process of polypropylene. The electrical treeing results are well verified with the simulation results, which offer a valuable tool for further analysis of the effect of intrinsic barrier height, hopping distance, and activation energy on the electrical degradation in the material. This work…

Recently, van der Waals (vdW) magnetic heterostructures have received increasing research attention in spintronics. However, the lack of room-temperature magnetic order of vdW materials has largely impeded its development in practical spintronic devices. Inspired by the lately discovered vdW ferromagnet Fe3GaTe2, which has been shown to have magnetic order above room temperature and sizable perpendicular magnetic anisotropy, we investigate the basic electronic structure and magnetic properties of Fe3GaTe2 as well as tunneling magnetoresistance effect in magnetic tunnel junctions (MTJs) with structure of Fe3GaTe2/insulator/Fe3GaTe2 by using first-principles calculations. It is found that Fe3GaTe2 with highly spin-polarized Fermi surface ensures that such magnetic tunnel junctions may have prominent tunneling magnetoresistance effect at room temperature even comparable to existing conventional AlOx and MgO-based MTJs. Our results suggest that Fe3GaTe2-based MTJs may be the promising candidate for realizing long-waiting full magnetic vdW spintronic devices.

In this Letter, we design Janus γ-Sn2XY (X/Y= S, Se, Te) monolayers and predict their piezoelectricity and carrier mobility by using first-principles simulations. Janus γ-Sn2XY are found to be indirect semiconducting characteristics with a camel's back-like dispersion in the top valence band. We discovered that Janus γ-Sn2XY are piezoelectric with high out-of-plane piezoelectric coefficients. Our calculated results for the piezoelectricity demonstrate that the out-of-plane piezoelectric coefficient d31 of Janus γ-Sn2STe is calculated to be 1.02 pm/V, larger than that of other 2D structures. Moreover, our calculations for the transport features reveal that while the carrier mobility of γ-Sn2SSe is directionally isotropic, the electron mobility of both γ-Sn2STe and γ-Sn2SeTe exhibit high anisotropy along the two transport directions. The Janus γ-Sn2XY monolayers have high electron mobility, especially the electron mobility of γ-Sn2STe exceeds 105 cm2 V–1 s–1, which is potential for nanoelectronic applications.

Two-dimensional (2D) ferromagnetic semiconductors (FMSs) hold exciting and promising potential for application in spintronic devices at the nanoscale. Currently, most 2D FMSs are based on 3d electrons; 4f electrons can provide nontrivial magnetism but have been much less studied to date. This paper presents a theoretical study, via first-principles calculations, of EuSn2X2 (X = P, As) monolayers based on rare-earth cations with f-electrons. The results show that EuSn2X2 monolayers possess a large magnetization (7 μB/Eu), a controllable magnetic anisotropy energy, and a unique d-electron-mediated f–f exchange mechanism. Both types of EuSn2X2 (X = P, As) monolayers are FMSs with indirect bandgaps of 1.00 and 0.99 eV, respectively, based on the Heyd–Scuseria–Ernzerhof (HSE06) method, which can be transform to direct bandgap semiconductors under biaxial strain. Interestingly, under the latter, spin–orbit coupling interaction gradually replaces the dipole–dipole interaction in the dominant position of magnetic anisotropy, resulting in the magnetic easy axis changing from in-plane to the…

Continuous-variable optical quantum information processing, where quantum information is encoded in a traveling wave of light called a flying qubit, is a candidate for a practical quantum computer with high clock frequencies. Homodyne detectors for quadrature-phase amplitude measurements have been the major factor limiting the clock frequency. Here, we developed a real-time amplitude measurement method using a modular optical parametric amplifier (OPA) and a broadband balanced photodiode that is commercially used for coherent wavelength-division multiplexing telecommunication of the fifth-generation mobile communication systems (5G). The OPA amplifies one quadrature-phase component of the quantum-level signal to a loss-tolerant macroscopic level and suppresses the loss after the OPA from 92.4% to only 0.4%. This method was applied to a broadband squeezed vacuum measurement with a center wavelength of 1545.32 nm. In the time-domain measurement, the squeezing level of 5.1 ± 0.1 dB without loss correction was obtained by a real-time oscilloscope with a sampling rate of 160 GHz and an…

Acoustic metamaterial represents the synergism between wave physics and designed geometric structures, aimed at novel acoustic properties. For the important functionality of acoustic absorption, metamaterials face the challenges posed by a mature, existing group of absorbing materials that have proven their effectiveness. Can the metamaterials do better? If so, at what price? This article aims to answer these important questions. In particular, it is shown that the critical advantage offered by metamaterial absorbers lies in the tunability of the absorption spectrum to fit the needs of the client, in conjunction with a minimum absorber thickness set by the causal constraint. By overcoming the obstacles set by the mass production cost, acoustic metamaterial absorbers have now entered the commercialization stage. We give three examples of the commercialized applications together with their underlying working principles and conclude with some observations.

Edge termination is the enabling building block of power devices to exploit the high breakdown field of wide bandgap (WBG) and ultra-wide bandgap (UWBG) semiconductors. This work presents a heterogeneous junction termination extension (JTE) based on p-type nickel oxide (NiO) for gallium oxide (Ga2O3) devices. Distinct from prior JTEs usually made by implantation or etch, this NiO JTE is deposited on the surface of Ga2O3 by magnetron sputtering. The JTE consists of multiple NiO layers with various lengths to allow for a graded decrease in effective charge density away from the device active region. Moreover, this surface JTE has broad design window and process latitude, and its efficiency is drift-layer agnostic. The physics of this NiO JTE is validated by experimental applications into NiO/Ga2O3 p–n diodes fabricated on two Ga2O3 wafers with different doping concentrations. The JTE enables a breakdown voltage over 3.2 kV and a consistent parallel-plate junction field of 4.2 MV/cm in both devices, rendering a power figure of merit of 2.5–2.7 GW/cm2. These results show the great…

We introduce vertical Schottky barrier diodes (SBDs) based on β-Ga2O3 with trench architecture, featuring a high-permittivity dielectric RESURF structure. These diodes are designed for application demanding high voltage and current capacities while maintaining ultra-low reverse leakage currents. The trench design plays a pivotal role in reducing the electric field at the metal–semiconductor junction, thereby yielding minimal reverse leakage attributed to field emission under high reverse bias conditions. Additionally, the incorporation of a high-k dielectric helps to suppress leakage through the trench bottom corner dielectric layer. The small area trench SBD (200 × 200 μm2) demonstrates a breakdown voltage exceeding 3 kV, accompanied by a reverse leakage current of less than 1 μA/cm2 at 3 kV. Moving on to larger area devices, the 1 × 1 and 2 × 2 mm2 devices exhibit breakdown voltages of 1.8 and 1.4 kV, while accommodating pulsed forward currents of 3.5 and 15 A, respectively. The capacitance, stored charge, and switching energy of the trench SBDs are also found to be less than the…

The widespread use of 4H silicon carbide (4H-SiC) is just around the corner since high-power electronics based on 4H-SiC are increasingly fabricated to enable the low-carbon development of the world. Quantum technologies are also intensively explored by scrutinizing 4H-SiC as a platform for wafer-scale integration of semiconductor and quantum technologies. Given the importance of impurities and defects for any semiconductor, comprehensive and insightful understanding of impurities and defects in 4H-SiC is imperative. In this Perspective, we summarize recent experimental and theoretical advances in researches on impurities and defects in 4H-SiC after briefly reviewing the history of 4H-SiC. Impurity engineering and defect engineering for the realization of the full potential of 4H-SiC are also discussed. Challenges for the study on impurities and defects in 4H-SiC are finally outlined.

Superhydrophobic surfaces have shown great application prospects due to their excellent water repellency in many applications involving fluid–surface interactions. As a ubiquitous fluid–surface interaction phenomenon, droplet impacting dynamics has a crucial effect on the application of superhydrophobic surfaces. In this Perspective, we summarize the basic process of droplet impacting on superhydrophobic surfaces and introduce the two most concerned parameters that describe the droplet impacting dynamics, i.e., the maximum spreading coefficient and the contact time. We then review two improvement strategies for superhydrophobic surfaces: one is to construct macrostructures and the other is to set wettability patterns on the surface. The former strategy shows great potential in reducing the droplet contact time, and the latter one can accurately regulate the behavior of impacting droplets. The motion of superhydrophobic surfaces also changes the droplet impacting dynamics due to the additional aerodynamic effect or energy input, which arouses attention recently. However, only the…

Physical reservoir computing (PRC) is thought to be a potential low training-cost temporal processing platform, which has been explored by the nonlinear and volatile dynamics of materials. An electric-double-layer (EDL) formed at the interface between a semiconductor and an electrolyte provided a great potential for building high energy-efficiency PRC. In this Letter, EDL coupled indium-gallium-zinc-oxide (IGZO) artificial synapses are used to implement reservoir computing (RC). Rich reservoir states can be obtained based the ionic relaxation-based time multiplexing mask process. Such an IGZO-based RC device exhibits nonlinearity, fade memory properties, and a low average power of ∼9.3 nW, well matching the requirement of a high energy-efficiency RC system. Recognition of handwritten digit and spoken-digit signals is simulated with an energy consumption per reservoir state of ∼1.9 nJ, and maximum accuracy of 90.86% and 100% can be achieved, respectively. Our results show a great potential of exploiting such EDL coupling for realizing a physical reservoir that would underlie a…

Magnetic nano-skyrmions develop quantized helicity excitations, and the quantum tunneling between nano-skyrmions possessing distinct helicities is indicative of the quantum nature of these particles. Experimental methods capable of nondestructively resolving the quantum aspects of topological spin textures, their local dynamical response, and their functionality now promise practical device architectures for quantum operations. With abilities to measure, engineer, and control matter at the atomic level, nano-skyrmions present opportunities to translate ideas into solid-state technologies. Proof-of-concept devices will offer electrical control over the helicity, opening a promising new pathway toward functionalizing collective spin states for the realization of a quantum computer based on skyrmions. This Perspective aims to discuss developments and challenges in this new research avenue in quantum magnetism and quantum information.

Multi-directional low-frequency vibration isolation is an unavoidable problem in many practical engineering scenarios. However, to date, most works are unable to achieve this goal, and those that can do so only to some degree, but their structure is complex and large, limiting the range of applications in practical engineering. Here, we propose a kind of quasi-zero stiffness (QZS) metamaterial constructed from a series of Kresling-pattern origami-inspired structures, whose simple topology with reasonable design parameters can obtain the expected QZS features. Moreover, the decoupling strategy adopted by the proposed QZS metamaterials allows for the independent motion of adjacent unit cells, resulting in an improvement in controllability and programmability. We demonstrate, both in simulations and experiments, the design process and the multi-directional low-frequency vibration isolation characteristics of the proposed QZS metamaterial. This study provides a method for realizing multi-directional low-frequency vibration isolation, expanding the application potential of QZS…

We report a series of deep learning models to solve complex forward and inverse design problems in molecular modeling and design. Using both diffusion models inspired by nonequilibrium thermodynamics and attention-based transformer architectures, we demonstrate a flexible framework to capture complex chemical structures. First trained on the Quantum Machines 9 (QM9) dataset and a series of quantum mechanical properties (e.g., homo, lumo, free energy, and heat capacity), we then generalize the model to study and design key properties of deep eutectic solvents (DESs). In addition to separate forward and inverse models, we also report an integrated fully prompt-based multi-task generative pretrained transformer model that solves multiple forward, inverse design, and prediction tasks, flexibly and within one model. We show that the multi-task generative model has the overall best performance and allows for flexible integration of multiple objectives, within one model, and for distinct chemistries, suggesting that synergies emerge during training of this large language model. Trained…

Thin-film lithium niobate (TFLN) photonic integrated circuits (PICs) have emerged as a promising integrated photonics platform for the optical communication, microwave photonics, and sensing applications. In recent years, rapid progress has been made on the development of low-loss TFLN waveguides, high-speed modulators, and various passive components. However, the integration of laser sources on the TFLN photonics platform is still one of the main hurdles in the path toward fully integrated TFLN PICs. Here, we present the heterogeneous integration of InP-based semiconductor lasers on a TFLN PIC. The III–V epitaxial layer stack is adhesively bonded to a TFLN waveguide circuit. In the laser device, the light is coupled from the III–V gain section to the TFLN waveguide via a multi-section spot size converter. A waveguide-coupled output power above 1 mW is achieved for the device operating at room temperature. This heterogeneous integration approach can also be used to realize on-chip photodetectors based on the same epitaxial layer stack and the same process flow, thereby enabling…

We demonstrate Schottky barrier engineering using PtOx/thin Pt Schottky contacts combined with edge termination using a high permittivity dielectric (ZrO2) field-plate for high-voltage vertical β-Ga2O3 diodes. A systematic study of baseline bare Pt/β-Ga2O3, PtOx/thin Pt/β-Ga2O3, and PtOx/β-Ga2O3 Schottky diode characteristics was performed, which revealed that the PtOx/thin Pt/β-Ga2O3 contact can combine the advantages of both PtOx and Pt, allowing better reverse blocking performance than plain metal Pt/β-Ga2O3 Schottky diodes and lower turn-on voltage than plain oxidized metal PtOx/β-Ga2O3 ones. Moreover, the thin Pt interlayer in the PtOx/thin Pt/β-Ga2O3 anode contact configuration, deposited by e-beam deposition, also provides plasma-free interface at the Schottky junction as opposed to the direct sputter deposited PtOx contacts of the PtOx/β-Ga2O3 diodes. We further implemented a high permittivity dielectric (ZrO2) field plate in PtOx/thin Pt/β-Ga2O3 diodes that assisted in edge-field management and enabled a breakdown voltage to ∼2.34 kV. These results indicate that the…

Vortex-induced vibration (VIV) and wake galloping are two aeroelastic instability phenomena with similar underlying mechanisms related to vortex shedding. Inspired by this common feature, a two-degree-of-freedom (2DOF) piezoelectric aeroelastic energy harvester (PAEH) is proposed, which employs VIV and wake galloping mechanisms with their respective benefits to improve the wind energy harvesting performance in a wide wind speed range. The proposed 2DOF PAEH overcomes the limitations of conventional one-degree-of-freedom VIV and wake galloping energy harvesters, with the former being only effective in a single and narrow lock-in wind speed range and the latter failing to work at low wind speeds. The modal frequencies of the 2DOF PAEHs are easily manipulated, and the twin mechanisms improve power generation over two lock-in regions at low wind speeds by the VIV mechanism and a third power generation region at relatively higher wind speeds due to wake galloping. A coupled aero-electro-mechanical model is developed and verified by wind tunnel experiments on a prototype. The results show…

We demonstrate the efficient generation of extreme ultraviolet (EUV) light from laser-produced plasma (LPP) driven by 2 μm wavelength laser light as an alternative for 10 μm CO2 gas LPP currently employed in EUV lithography machines for high-volume manufacturing of semiconductor devices. High conversion efficiencies of laser light into “in-band” EUV photons up to 5.0% are achieved by homogeneously heating the plasma that is laser-generated from preshaped tin microdroplet targets. Scaling the laser pulse duration, spot size, and intensity yields a high in-band EUV energy output of up to 12.5 mJ. The EUV emission source size is studied under a similar parameter range and is shown to match typical etendues of EUV optic columns. Our findings make 2 μm LPP a particularly promising candidate to power future EUV nanolithography.

Learning and pattern recognition inevitably requires memory of previous events, a feature that conventional CMOS hardware needs to artificially simulate. Dynamical systems naturally provide the memory, complexity, and nonlinearity needed for a plethora of different unconventional computing approaches. In this perspective article, we focus on the unconventional computing concept of reservoir computing and provide an overview of key physical reservoir works reported. We focus on the promising platform of magnetic structures and, in particular, skyrmions, which potentially allow for low-power applications. Moreover, we discuss skyrmion-based implementations of Brownian computing, which has recently been combined with reservoir computing. This computing paradigm leverages the thermal fluctuations present in many skyrmion systems. Finally, we provide an outlook on the most important challenges in this field.

To support the ever-growing demand for faster, energy-efficient computation, more aggressive scaling of the transistor is required. Two-dimensional (2D) transition metal dichalcogenides (TMDs), with their ultra-thin body, excellent electrostatic gate control, and absence of surface dangling bonds, allow for extreme scaling of the channel region without compromising the mobility. New device geometries, such as stacked nanosheets with multiple parallel channels for carrier flow, can facilitate higher drive currents to enable ultra-fast switches, and TMDs are an ideal candidate for that type of next generation front-end-of-line field effect transistor (FET). TMDs are also promising for monolithic 3D (M3D) integrated back-end-of-line FETs due to their ability to be grown at low temperature and with less regard to lattice matching through van der Waals (vdW) epitaxy. To achieve TMD FETs with superior performance, two important challenges must be addressed: (1) complementary n- and p-type FETs with small and reliable threshold voltages are required for the reduction of dynamic and static…

MXene's two-dimensional (2D) morphology, metallic electrical conductivity, and optical transparency characteristics have been widely utilized to uplift the performance of diverse optoelectronic devices. In this study, we demonstrate a simple spin-coating of 2D MXene nanosheets on 1D GaN nanorods (NRs) to establish a van der Waals (vdW) Schottky junction, which is efficient to detect UV radiation (λ = 382 nm) without requiring the external power supply. The built-in electric field developed through vdW Schottky junction formation stimulates the separation of electron–hole pairs and thereby facilitates the MXene/GaN NRs device to exhibit better UV detection performance than the pristine GaN NRs device. The performance of both pristine GaN and MXene/GaN NRs devices is compared by tuning the UV radiation power density in the range of 0.33–1.35 mW/cm2. Notably, the self-powered MXene/GaN NRs photodetector demonstrated the characteristics of high photoresponsivity (48.6 mA/W), detectivity (5.9 × 1012 Jones), and external quantum efficiency (543%). These characteristics signify the…

We investigate electronic transport properties of copper–graphene (Cu–G) composites using a density-functional theory (DFT) framework. Conduction in composites is studied by varying the interfacial distance of copper/graphene/copper (Cu/G/Cu) interface models. Electronic conductivity of the models computed using the Kubo–Greenwood formula shows that the conductivity increases with decreasing Cu–G distance and saturates below a threshold Cu–G distance. The DFT-based Bader charge analysis indicates increasing charge transfer between Cu atoms at the interfacial layers and the graphene with decreasing Cu–G distance. The electronic density of states reveals increasing contributions from both copper and carbon atoms near the Fermi level with decreasing Cu–G interfacial distance. By computing the space-projected conductivity of the Cu/G/Cu models, we show that the graphene forms a bridge to the electronic conduction at small Cu–G distances, thereby enhancing the conductivity.

In this paper, oriented hBN composites with anisotropic thermal conductivity are employed to improve electrical resistivity-temperature characteristics, thus inhibiting the occurrence of DC surface flashover under the temperature gradient by directionally manipulating heat flow. The DC surface flashover performance, electrical resistivity, carrier mobility, and electric field distribution of composites depending on the hBN orientation are studied at different temperatures. When the angle between the hBN basal plane and the axis of the electrodes is 90°, the out-of-plane oriented hBN composite shows the best electrical resistivity-temperature characteristics than that of the polymer filled with ceramic particles of positive temperature coefficient, whose surface flashover voltage is 28% higher than that of the out-of-plane oriented hBN composite with the angle of 0° between the hBN basal plane and the axis of the electrodes under the high-voltage electrode heated at 160 °C. The least rise in carrier mobility and electric field intensity near the GND electrode is the main factor in…

Plasmonics represents a unique approach to confine and enhance electromagnetic radiation well below the diffraction limit, bringing a huge potential for novel applications, for instance, in energy harvesting, optoelectronics, and nanoscale biochemistry. To achieve novel functionalities, the combination of plasmonic properties with other material functions has become increasingly attractive. In this Perspective, we review the current state of the art, challenges, and future opportunities within the field of magnetoplasmonics in confined geometries, an emerging area aiming to merge magnetism and plasmonics to either control localized plasmons, confined electromagnetic-induced collective electronic excitations, using magnetic properties, or vice versa. We begin by highlighting the cornerstones of the history and principles of this research field. We then provide our vision of its future development by showcasing raising research directions in hybrid magnetoplasmonic systems to overcome radiation losses and novel materials for magnetoplasmonics, such as transparent conductive oxides and…

Designing direct Z-scheme heterostructure photocatalysts has received enormous attention due to the efficient separation of photo-generated carriers in water splitting. Based on first-principles calculations, electronic properties and a photocatalytic mechanism of a GeC/HfS2 van der Waals (vdW) heterostructure are systematically explored. From the analysis of band arrangement and the built-in electric field, the heterostructure, with an indirect bandgap of 0.40 eV, is demonstrated to be a typical direct Z-scheme system. Remarkably, there is also a 0.40 eV interlayer work function difference in the heterostructure, which is helpful to further drive carrier separation and enhance the water splitting ability by partially bending the redox potential of water. The Gibbs calculation shows that the GeC/HfS2 vdW heterostructure can achieve overall photocatalytic water splitting spontaneously under neutral conditions. Moreover, excellent visible light absorption ability (∼5×105 cm−1) and giant carrier mobilities (5823 cm2 V−1 s−1) also make GeC/HfS2 heterostructure highly competitive in…

Superhydrophobicity is a remarkable adaptation observed in various natural surfaces, which can potentially play a crucial role in the efficient functioning of numerous applications. The attainment of long-lasting or “durable” superhydrophobicity has significant implications for global energy production, water conservation, and the overall carbon footprint of industrialized and developing nations. Many applications requiring superhydrophobicity have been limited to laboratory scale experiments due to poor durability. In this article, we discuss important recent advancements and challenges to the development of durable superhydrophobic surfaces, including scalable fabrication, efficacy with low surface tension fluids, and the absence of standardized durability testing methods. To help address these challenges that hinder the implementation of superhydrophobicity, we conclude the article by providing a roadmap that outlines the crucial areas where the community should focus its research and development efforts, both from a fundamental and applied perspective.

Non-reciprocal charge transport in supercurrent diodes (SDs) has polarized growing interest in the last few years for their potential applications in superconducting electronics (SCE). So far, SD effects have been reported in complex hybrid superconductor/semiconductor structures or metallic systems subject to moderate magnetic fields, thus showing limited potentiality for practical applications in SCE. Here, we report the design and realization of a monolithic device that shows a valuable SD effect by exploiting a Dayem bridge-based superconducting quantum interference device. Our structure allows reaching rectification efficiencies (η) up to ∼6%. Moreover, the absolute value and the polarity of η can be selected on demand by the modulation of an external magnetic flux or by a gate voltage, thereby guaranteeing high versatility and improved switching speed. Furthermore, our SD operates in a wide range of temperatures up to about 70% of the superconducting critical temperature of the titanium film composing the interferometer. Our SD effect can find extended applications in SCE by…

The development of photonic integrated circuits has historically been driven by communications. However, emerging markets and opportunities require platforms that can operate over a broader wavelength range, offer additional capabilities, or improve performance. This paper provides a perspective on these emerging opportunities and the most promising approaches for addressing them, with a focus on platforms that support on-chip light generation and amplification.

We grow strained Ge/SiGe heterostructures by reduced-pressure chemical vapor deposition on 100 mm Ge wafers. The use of Ge wafers as substrates for epitaxy enables high-quality Ge-rich SiGe strain-relaxed buffers with a threading dislocation density of (6±1)×105 cm−2, nearly an order of magnitude improvement compared to control strain-relaxed buffers on Si wafers. The associated reduction in short-range scattering allows for a drastic improvement of the disorder properties of the two-dimensional hole gas, measured in several Ge/SiGe heterostructure field-effect transistors. We measure an average low percolation density of (1.22±0.03)×1010 cm−2 and an average maximum mobility of (3.4±0.1)×106 cm2/Vs and quantum mobility of (8.4±0.5)×104 cm2/Vs when the hole density in the quantum well is saturated to (1.65±0.02)×1011 cm−2. We anticipate immediate application of these heterostructures for next-generation, higher-performance Ge spin-qubits, and their integration into larger quantum processors.

Self-powered ultraviolet (UV) photodetectors (PDs) based on GaN have been of great importance in the application of UV communication, thanks to its wide direct bandgap and strong resistance to irradiation. However, current self-powered GaN-based heterojunction UV photodetectors could not meet the requirement of fast photoresponse. Herein, type-II pn heterojunction GaS/GaN-based self-powered PDs have been proposed with a naturally p-type doping GaS thin film grown on n-type GaN via chemical vapor deposition. The electronic and optical properties of GaS/GaN heterojunction were investigated via experiments and the density functional theory. Afterward, as-prepared GaS/GaN-based PDs reveal an excellent self-powered photosensitivity/detectivity of 6.26 mA W−1/8.29 × 109 Jones at 0 V at 365 nm, ultrafast response speed with a rise/fall time of 48/80 μs as well as an amazing rejection ratio (R365 nm/R500 nm) of 3.42 × 104, and a fine rectification ratio of 105.9. This work provides a feasible method to synthesize high-performance GaS/GaN heterojunctions and demonstrates their enormous…

We demonstrate a high dynamic range Josephson parametric amplifier (JPA) in which the active nonlinear element is implemented using an array of rf-SQUIDs. The device is matched to the 50 Ω environment with a Klopfenstein-taper impedance transformer and achieves a bandwidth of 250–300 MHz with input saturation powers up to −95 dBm at 20 dB gain. A 54-qubit Sycamore processor was used to benchmark these devices, providing a calibration for readout power, an estimation of amplifier added noise, and a platform for comparison against standard impedance matched parametric amplifiers with a single dc-SQUID. We find that the high power rf-SQUID array design has no adverse effect on system noise, readout fidelity, or qubit dephasing, and we estimate an upper bound on amplifier added noise at 1.6 times the quantum limit. Finally, amplifiers with this design show no degradation in readout fidelity due to gain compression, which can occur in multi-tone multiplexed readout with traditional JPAs.

We report significantly enhanced device performance in long wavelength interband cascade lasers (ICLs) by employing a recently proposed innovative quantum well (QW) active region containing strained InAsP layers. These ICLs were able to operate at wavelengths near 14.4 μm, the longest ever demonstrated for III–V interband lasers, implying great potential of ICLs to cover an even wider wavelength range. Also, by applying the aforesaid QW active region configuration on ICLs at relatively short wavelengths, ICLs were demonstrated at a low threshold current density (e.g., 13 A/cm2 at 80 K) and at temperatures up to 212 K near 12.4 μm, more than 50 K higher than the previously reported ICLs with the standard W-shape QW active region at similar wavelengths. This suggests that the QW active region with InAsP layers can be used to improve device performance at the shorter wavelengths.

A rapid surge in the research on very low frequency (VLF) antennas is occurring due to the demand for radio navigation and special environment communications such as underwater and underground applications. Among them, magnetoelectric (ME) antennas have recently proven to be a prospective solution for miniaturization of VLF communication systems. However, the essential magnetic bias fields (Hdc) lead to challenges of miniaturization, electromagnetic interference, and noise sources for ME antenna application. Here, a bias-free VLF ME antenna based on the magneto-gradient ME composite (i.e., annealed Metglas/Metglas/PZT/Metglas/annealed Metglas) has been designed. Owing to the interaction effect between multi-unannealed/annealed Metglas, the magneto-gradient ME composite exhibits a large direct and converse ME response (αDME = 107 V/cm Oe and αCME = 9 Gs/V at resonance) at bias-free, which is about 63% and 33% of the maximum value under optimal magnetic bias for unannealed ME composites. Moreover, a digital amplitude shift keying (ASK) modulation method is proved suitable for the…

Although near-field radiative heat transfer was introduced in the 1950s, interest in the field has only recently revived, as the effect promises improved performance in various applications where contactless temperature regulation in the small-scale is a requirement. With progress in computational electromagnetics as well as in nanoinstrumentation, it has become possible to simulate the effect in complex configurations and to measure it with high precision. In this Perspective, we highlight key theoretical and experimental advances in the field, and we discuss important developments in tailoring and enhancing near-field thermal emission and heat transfer. We discuss opportunities in heat-to-electricity energy conversion with thermophotovoltaic systems, as well as non-reciprocal heat transfer, as two of many recent focus topics in the field. Finally, we highlight key experimental challenges and opportunities with emerging materials, for probing near-field heat transfer for relevant technologies in the large-scale.

Recent observation of high density polarization-induced two-dimensional electron gases in ultra-thin N-polar GaN layers grown on single-crystal AlN has enabled the development of N-polar high electron mobility transistors (HEMTs) on AlN. Such devices will take advantage of thermal and power handling capabilities of AlN, while simultaneously benefitting from the merits of N-polar structures, such as a strong back barrier. We report the experimental demonstration of N-polar GaN/AlGaN/AlN HEMTs on single-crystal AlN substrates, showing an on-current of 2.6 A/mm with a peak transconductance of 0.31 S/mm. Small-signal RF measurements revealed speeds exceeding ft/fmax = 68/100 GHz. These results pave the way for developing RF electronics with excellent thermal management based on N-polar single-crystal AlN.

We demonstrate epitaxial lattice-matched Al0.89Sc0.11N/GaN 10 and 20 period distributed Bragg reflectors (DBRs) grown on c-plane bulk n-type GaN substrates by plasma-assisted molecular beam epitaxy. Resulting from a rapid increase in in-plane lattice coefficient as scandium is incorporated into AlScN, we measure a lattice-matched condition to c-plane GaN for a Sc content of just 11%, resulting in a large refractive index mismatch Δn greater than 0.3 corresponding to an index contrast of Δn/nGaN = 0.12 with GaN. The DBRs demonstrated here are designed for a peak reflectivity at a vacuum wavelength of 400 nm, reaching a reflectivity of 0.98 for 20 periods. It is highlighted that AlScN/GaN multilayers require fewer periods for a desired reflectivity than other lattice-matched Bragg reflectors such as those based on AlInN/GaN multilayers.

Far-ultraviolet-C (far-UVC) light-emitting diodes (LEDs) with an emission wavelength of 234 nm with different polarization-doped AlGaN hole injection layers (HILs) are compared regarding their emission power, voltage, and leakage current. The influence of the thickness of the polarization-doped layer (PDL), an additional Mg doping of the PDL, as well as a combination of a PDL with a conventionally Mg-doped AlGaN HIL will be discussed. The different PDL thicknesses show nearly no influence on the emission power or voltage. However, the leakage current of the LEDs below the turn-on voltage decreases with an increasing thickness of the PDL. In contrast, an additional Mg doping of the PDL ([Mg] ∼ 1.5 × 1019 cm−3) results in a fivefold decrease in the emission power at an unchanged voltage and leakage current. Finally, a combination of a PDL and a conventionally Mg-doped AlGaN layer ([Mg] ∼ 1.5 × 1019 cm−3) as a HIL shows also a similar emission power and voltage compared to the single PDL, but the leakage current increases. Based on these optimizations, 234 nm LEDs were realized with a…

The Rydberg atom-based microwave electric field sensor has high sensitivity for weak RF-field detection. Selection of Rydberg states with larger electric dipole moment is beneficial to enhance the sensitivity, and we choose Rydberg states with its principal quantum number up to n ∼ 80. We study the probe laser transmission response to a microwave field for these chosen high Rydberg states at room temperature. It agrees well with theoretical simulation based on an optical Bloch equation with considered microwave-atom interaction and Doppler broadening effect. In our experiment, the microwave sensing sensitivity based on 85 Rb transition | 78 S 1 / 2 ⟩ → | 78 P 3 / 2 ⟩ arrives at 5.102(49) nV cm − 1 Hz − 1 / 2 at 1 kHz.

Nanomechanics, nanoacoustics, and nanophononics refer to the engineering of acoustic phonons and elastic waves at the nanoscale and their interactions with other excitations, such as magnons, electrons, and photons. This engineering enables the manipulation and control of solid-state properties that depend on the relative positions of atoms in a lattice. The access to advanced nanofabrication and novel characterization techniques enabled a fast development of the fields over the last decade. The applications of nanophononics include thermal management, ultrafast data processing, simulation, sensing, and the development of quantum technologies. In this review, we cover some of the milestones and breakthroughs and identify promising pathways of these emerging fields.

Non-contact quartz-enhanced photoacoustic spectroscopy (NC-QEPAS) was proposed and developed for trace gas analysis. The NC-QEPAS aims at solving the problem that the quartz tuning fork (QTF) must be immersed in the gases for photoacoustic wave transducing, which limits its application for corrosive and dusty gas sensing. In this work, the QTF was isolated from the gas, realizing “non-contact” detection. An elastic parylene film was synthesized and then patched to the slit of a QEPAS gas cell. With an optimized coupling effect, the parylene film shows a resonance enhancement with the QTF and acoustic micro-resonator, realizing non-contact photoacoustic detection of gas. The NC-QEPAS not only increases the photoacoustic signal amplitude but also decreases the background noise. Compared to traditional contact QEPAS with QTF immersed in the gas, the NC-QEPAS shows a signal-to-noise enhancement factor of 13. A normalized noise equivalent absorption coefficient of 8.8 × 10−9 cm−1 W Hz−1/2 was achieved. Allan deviation shows good long-term stability of the NC-QEPAS sensor. With an…

As engineered electromagnetic covers based on (space-) time modulated metamaterials and metasurfaces, Doppler cloaks are able to compensate the Doppler effect induced by the motion of a scatterer, making it appear as if it were at rest to a detecting radar system. Perfect Doppler compensation can be theoretically always achieved for any relative velocity and motion direction of the cloaked scatterer with respect to the detecting system. However, the motion can be still detected from the cross section variation of the Doppler cloaked scatterer, especially under oblique incidence illumination. The challenge is, therefore, to have a proper Doppler compensation and maintain the amount of scattered energy toward the detection system as much constant as possible with respect to the illumination angle. In this Letter, we propose the design of self-adaptive retro-reflective planar Doppler cloak composed of a pair of space-time modulated metasurfaces: the first metasurface focuses the incident field in a specific location on the second metasurface, which is designed for enabling…

Magnons, the quanta of collective spin excitations in magnetically ordered materials, have distinct properties that make them uniquely appealing for quantum information applications. They can have ultra-small wavelengths down to the nanometer scale even at microwave frequencies. They can provide coupling to a diverse set of other quantum excitations, and their inherently gyrotropic dynamics forms the basis for pronounced nonreciprocities. In this article, we discuss what the current research challenges are for integrating magnetic materials into quantum information systems and provide a perspective on how to address them.

AlGaN-based far-UVC light emitting diodes (LEDs) with an emission wavelength of 233 nm were fabricated in the form of micro-LED arrays with emitter diameters ranging from 1.5 to 50 μm. The mesa was plasma etched with a sidewall angle of 45°–50°, and insulator layers made of SiNx or SiO2 were deposited. While the external quantum efficiency (EQE) of the LEDs with SiNx showed only a small dependency on the micro-LED diameter, the LEDs using SiO2 showed an increase in the peak EQE by a factor of four as compared to large area devices. This enhancement is attributed to a strong increase in the light extraction efficiency due to total internal reflection and re-direction at the inclined mesa, allowing TM-polarized light emitted in the plane of the quantum well to be extracted through the sapphire backside of the chips.

Lithium–sulfur (Li–S) batteries have attracted increasing attention for next-generation energy storage systems with a high energy density and low cost. However, the practical applications have been plagued by the sluggish reaction kinetics and the shuttle effect of lithium polysulfides (LiPSs). Herein, core–shell SiO2@Ti3C2Tx MXene (SiO2@MX) hollow spheres are constructed as multifunctional catalysts to boost the performance of Li–S batteries. The dual-polar and dual-physical properties of SiO2 core and MXene shell provide multiple defense lines to the shuttle effect by chemical and physical confinement to LiPSs. Density functional theory calculations prove that Ti3C2Tx MXene and SiO2 enable the stronger trapping ability of LiPSs and the fast Li2S decomposition process. With this strategy, the robust SiO2@MX/S electrodes deliver superior electrochemical performances, including a high capacity of 1263 mAh g−1, and remarkable cycling stability with an ultralow capacity decay of 0.04% per cycle over 1000 cycles at 1 C. This work highlights the significance of core-shell dual-polar…

Low-frequency (LF) magnetoelectric (ME) antennas are of great importance in implantable medical device (IMD) applications compared to their electromagnetic (EM) counterparts as they can potentially offer appropriate size miniaturization and lower path loss and higher efficiency. In this work, a self-biased, miniaturized LF ME antenna is proposed, which operates at its electromechanical resonant frequency of 49.9 kHz, with the size scaled down to only 1.75 mm3, which is significantly smaller than that of a comparable EM antenna. The proposed antenna that constitutes of a piezoelectric layer sandwiched between two magnetostrictive layers is characterized in both air and an optimized three-layered human tissue-mimicking phantom media to demonstrate the potential applications in deep-body communications. The near field radiation pattern of the ME antenna is measured experimentally. The maximum received power obtained at a distance of 1.2 m in air and phantom media is 20 and 8 nW, respectively. The proposed antenna has significantly lower path loss of 0.57 dB/m as compared to its higher…

Dielectric capacitors own great potential in next-generation energy storage devices for their fast charge-discharge time, while low energy storage capacity limits their commercialization. Enormous lead-free ferroelectric ceramic capacitor systems have been reported in recent decades, and energy storage density has increased rapidly. By comparing with some ceramic systems with fashioned materials or techniques, which lacks repeatability, as reported latterly, we proposed a unique but straightforward way to boost the energy storage capacity in a modified conventional ferroelectric system. Through stoichiometric ratio regulation, the coexistence of the C-phase and T-phase was obtained in 0.85(Ba1-xCax)(ZryTi1-y)O3-0.15BiSmO3-2 wt. % MnO ceramics with x = 0.1 and y = 0.15 under the proof of the combination of Rietveld XRD refinement and transmission electron microscope measurement. The Wrec of 3.90 J/cm3, an excellent value for BCZT-based ceramic at the present stage, was obtained because of the co-contribution of the optimization of electric field distribution and the additional…

The two-dimensional (2D) transition metal carbide Ti3C2Tx MXene is a potential candidate for efficient electromagnetic wave absorbers due to its excellent intrinsic conductivity and structural machinability. However, Ti3C2Tx MXene also has some problems (such as self-stacking and single loss mechanism) that limit its practical electromagnetic wave absorption. Based on the electromagnetic wave absorption mechanism, electromagnetic responsiveness of absorbers can be modulated by designing the composition and structure. Herein, a 1D/2D Co/Co9S8/Ti3C2Tx composite has been synthesized by assembling 2D Ti3C2Tx MXene with the designed 1D magnetic structure. The 1D Co/Co9S8 was designed as a core-sheath structure that avoids magnetic agglomeration, and the assembly with 2D Ti3C2Tx sheets alleviates the self-stacking problem of Ti3C2Tx MXene sheets. More importantly, the magnetic component enriches the electromagnetic wave dissipation mechanism, and the multiple heterojunction surfaces provide strong polarization loss capability for the Ti3C2Tx MXene-based absorber. Benefiting from the…

Conventional neural structures tend to communicate through analog quantities, such as currents or voltages; however, as CMOS devices shrink and supply voltages decrease, the dynamic range of voltage/current-domain analog circuits becomes narrower, the available margin becomes smaller, and noise immunity decreases. More than that, the use of operational amplifiers (op-amps) and continuous-time or clocked comparators in conventional designs leads to high energy consumption and large chip area, which would be detrimental to building spiking neural networks. In view of this, we propose a neural structure for generating and transmitting time-domain signals, including a neuron module, a synapse module, and two weight modules. The proposed neural structure is driven by a leakage current of MOS transistors and uses an inverter-based comparator to realize a firing function, thus providing higher energy and area efficiency compared to conventional designs. The proposed neural structure is fabricated using a TSMC 65 nm CMOS technology. The proposed neuron and synapse occupy the area of 127 and…

We report the observation of the orbital counterpart of the spin Hall magnetoresistance (SMR): the orbital Hall magnetoresistance (OMR). We measured angular-dependent longitudinal magnetoresistance for Ni/Ti bilayer and Ni single-layer films by rotating a magnetic field along three orthogonal planes. When the magnetic field is rotated in the plane perpendicular to the applied current direction, the angular dependence of the magnetoresistance in the Ni/Ti bilayers is consistent with the prediction of the SMR and OMR, whereas that in the Ni single-layer film can be attributed to the geometrical size effect of the anisotropic magnetoresistance. In the Ni/Ti bilayers, the magnetoresistance ratio is found to be five orders of magnitude larger than the prediction of the SMR, indicating that the OMR plays a dominant role in this system.

The accurate description of phonon dispersion of two-dimensional (2D) materials demonstrates significance in many research fields of condensed matter physics. In this paper, we systematically calculate the phonon spectra and transport properties of six representative 2D materials (encompassing single-element and binary compounds with flat, buckled, and puckered backbone geometries) by means of density functional theory (DFT) and two machine learning interatomic potentials [MLIPs, on-the-fly machine learning potential (FMLP), and moment tensor potential (MTP)]. The results show that the acoustic out-of-plane flexural (ZA) dispersion of the 2D materials are always and easily exhibiting non-quadratic dispersion phenomena near the center of the Brillouin zone by using the pure DFT calculation method. This phenomenon contradicts physics and reflects intuitively from the non-zero group velocity at Γ point. However, no matter which MLIP (FMLP/MTP) the calculation is based on, it could solve such behavior perfectly, where the ZA mode conforms to the quadratic dispersion relationship in the…

Despite its scalability and CMOS process compatibility, the limited endurance and sub-optimal stress response of ferroelectric Zr-substituted hafnia [(Hf,Zr)O2] have been one of the key impediments toward its integration into practical device and technology applications. Here, using electrical measurements complemented by photoluminescence spectroscopy, we investigate the underlying mechanisms behind this behavior in 10 nm thick W/Hf0.5Zr0.5O2/W capacitors. Analyzing the evolution of leakage current with stress cycles and the spectroscopic response of the stress-induced leakage current, we attribute the behavior to defect levels, which lie at 0.6 eV from the conduction band edge of the ferroelectric. Photoluminescence spectroscopy, in turn, further corroborates the defect level's position within the bandgap while enabling its attribution to the presence of oxygen vacancies. This work helps to identify oxygen vacancies as the key factor responsible for the degraded endurance and stress response in (Hf,Zr)O2 and subsequently motivates the exploration of methods to reduce the oxygen…

Integration of β-Ga2O3 with high thermal conductivity materials such as diamond has been considered due to β-Ga2O3's low and anisotropic thermal conductivity, reaching only 27 W m–1 K–1. However, the effect of crystallographic orientation on thermal interface resistance has not been studied extensively, which is relevant for potential device architectures. In this work, we use molecular dynamics simulations to investigate the crystal orientation-dependent thermal boundary resistance (TBR) across van der Waals bonded diamond–β-Ga2O3 and ionicly bonded amorphous Al2O3–β-Ga2O3 interfaces. Al2O3 is often used as interlayer to grow diamond onto Ga2O3. We find that TBR values across the van der Waals interface may vary by up to 70% depending on the orientation of the β-Ga2O3, while the Al2O3–β-Ga2O3 TBR values remain around 0.9 ± 0.3 m2 KGW−1. We, thus, conclude on the optimal direction of β-Ga2O3 to use for reducing the TBR in these heterostructures.

Ga2O3 is an ultrawide-bandgap semiconductor with a variety of crystal configurations, which has the potential for a variety of applications, especially in power electronics and ultraviolet optoelectronics. However, there has been no single interatomic potential reported for Ga2O3 polymorphs in terms of molecular dynamics prediction of thermal conductivity. Here, one interatomic potential has been developed based on neural networks, which has the clear advantages of consuming less computational power than density functional theory and has high accuracy in predicting the thermal conductivity of the three polymorphs of Ga2O3. Using the neuroevolution potential, the thermal conductivity values at 300 K have been predicted. Hence, the κ[average-α] was 67.2% that of β-Ga2O3, and the κ[average-ε] was only 26.4% that of β-Ga2O3. The possible reasons for the discrepancies in thermal conductivity values in various crystal types and orientations have been explored. As a result, it could be shown that the contribution of low-frequency phonons to thermal conductivity was very significant in…

The Schottky–Mott (S–M) limit based on the S–M rule is often used to evaluate the Schottky barrier height (SBH) at metal–semiconductor (MS) van der Waals (vdW) contacts but fails at the polar interfaces. In order to extend the S–M rule to the polar interfaces, we here modify the S–M equation to predict the SBH at vdW interfaces of 2D Janus materials, taking into account the effects of intrinsic and interface dipoles. The modified S–M equation is verified based on the first-principles calculations of the MoSi2As2P2/HTaSe2F vdW interfaces, showing a sharp dependence of SBH on the dipole amplitude and direction. Specifically, n-type Schottky barriers tend to form when a semiconductor contacts with a low-work-function surface of Janus metal or a metal interfaces to the high-electron-affinity surface of Janus semiconductor; otherwise, a p-type one is preferable. Interestingly, the smallest n(p)-type SBH could be attained when both intrinsic dipole directions are the same. This work demonstrates that the S–M rule can be extended to the polar interfaces and dipole engineering is an…

Photomultiplication type quasi-planar all-polymer photodetectors (PM-QAPDs) are fabricated with P3HT/PY-IT as active layers by employing a sequential spin-coating method. The part of PY-IT can penetrate into a P3HT layer to emerge isolated electron-traps formed with PY-IT surrounded by P3HT. The trapped electron distribution near an Al electrode will determine the spectral response range of PM-QAPDs. Broadband PM-QAPDs can be achieved with a 0.25 μm thick P3HT layer and a ultra-thin PY-IT layer prepared from 1 mg/ml solution, exhibiting a broad response from 320 to 870 nm. An external quantum efficiency (EQE) value of optimal PM-QAPDs approaches 16 000% at 360 nm under −12 V bias. When the thickness of the P3HT layer is increased to 2.4 μm, the PM-QAPDs exhibit a narrowband response from 630 to 870 nm, which can be well explained according to the Beer–Lambert law. The work may provide a smart strategy to adjust response range of PM-QAPDs by alerting the thickness of the donor layer.

In this research, β-Ga2O3/NiO heterostructures were grown directly on CeO2 buffered Hastelloy flexible substrates. With pulsed laser deposition under high temperatures, as-grown β-Ga2O3 and NiO thin films have a preferred out-of-plane orientation along the ⟨−201⟩ and ➎111➉ directions. This is due to the ideal epitaxial ability of the CeO2 buffer layer, which serves as a perfect template for the epitaxial growth of single-oriented NiO and β-Ga2O3 by creating a constant gradient from CeO2 (2.7 Å along ➎001➉) to NiO (2.9 Å along ➎110➉), and eventually to β-Ga2O3 (3.04 Å along ➎010➉). The Hastelloy substrates endow photodetectors with good deformability and mechanical robustness. Moreover, owing to the type-II band alignment of β-Ga2O3/NiO heterostructures, the photodetectors have a good photocurrent at zero bias under 284 nm of light illumination. In addition, the photocurrent is significantly higher than when using an analogous heterostructure (as described in some previous reports), because the β-Ga2O3 and NiO thin films are crystalized along a single orientation with fewer defects.

In this work, IrMn-based perpendicular magnetic tunnel junctions (MTJs) are investigated. By inserting a thin W layer at an antiferromagnet/ferromagnet (AFM/FM) interface, we enhance the annealing temperature to 355 °C and obtain a high tunnel magnetoresistance ratio of 127%. Subsequently, field-free spin–orbit torque (SOT) switching of perpendicular MTJ is realized thanks to the in-plane exchange bias generated at the AFM/FM interface. Moreover, by applying a gate voltage, a coercive field is effectively decreased due to the voltage-controlled magnetic anisotropy (VCMA) effect. Finally, through the interplay of the SOT and VCMA effects, the critical switching current density is dramatically reduced by 73% (to 2.4 MA/cm2) and the total writing power consumption is decreased by 84% when a gate voltage of 0.76 V is applied. These findings pave the way for the practical applications of the IrMn-based perpendicular MTJs in low-power magnetic random-access memory.

Artificial neural networks built with optoelectronic synaptic devices have been proven to process visual information effectively. However, it takes great latency time and energy consumption, especially facing dynamic visual information, due to the separated optical sensor, memory, and process unit. Reservoir computing (RC) based on optoelectronic synaptic devices provides an in-sensor RC for processing temporal information efficiently. It achieves efficient computation by sensing and processing optical signals directly with optoelectronic synaptic devices. Optoelectronic synaptic devices shine in visual information processing, whose application in visual sensing and processing will provide a viable hardware solution for in-sensor computing. Therefore, the application of optoelectronic synaptic devices in reservoir computing has prompted increasing attention. Herein, for promoting the application of physical reservoir computing (PRC) with optoelectrical synapses in machine vision, synaptic plasticity will be introduced first in this work and then illustrate the basic functions of…

We demonstrate photon-counting single-pixel imaging in the ultraviolet region. Toward this target, we develop a high-performance compact single-photon detector based on a 4H-SiC single-photon avalanche diode (SPAD), where a tailored readout circuit with active hold-off time is designed to restrain detector noise and operate the SPAD in the free-running mode. We use structured illumination to reconstruct 192 × 192 compressed images at a 4 fps frame rate. To show the superior capability of ultraviolet characteristics, we use our single-pixel imaging system to identify and distinguish different transparent objects under low-intensity irradiation and image ultraviolet light sources. The results provide a practical solution for general ultraviolet imaging applications.

Optical image edge detection manifests itself as the advantages of fast speed, low energy consumption, parallel operation, and large information capacity, playing a crucial role in object and image recognition in the realms of biology, medicine, and artificial intelligence. In this paper, a dielectric metasurface that can achieve object edge detection in the full visible band is proposed. By combining two optical differential methods referring to spatial spectrum-dependent transmission function and 4f system-based spatial spectrum phase shift, a tetratomic macropixel metasurface that enables polarization-correlated interference based on dual geometric phase modulation is designed, which can achieve object edge detection under 473, 530, and 633 nm wavelengths, and even under white light conditions. This coherent filtering metasurface operator provides a flexible approach for achieving wideband two-dimensional edge detection.

0.9Ba(Ti1−xMgx)O3−x-0.1NaNbO3 (BTNN-100xMg) solid solutions are investigated with a view to developing Bi, Pb, and rare earth free, high voltage multilayer ceramic capacitors. Mg doping on the B-site significantly reduced the electronic conductivity and resulted in ceramics that could withstand a pulsed unipolar field of >300 kV/cm (Emax) to give a recoverable energy density of 3.4 J/cm3 at 82.6% efficiency for x = 0.01. The high Emax is accompanied by a high dielectric permittivity (ε′ ∼ 1700 at room temperature) with temperature-stable dielectric permittivity of Δε/ε298K ≤ ±15% and loss tangent tan δ < 0.02 from 116 to 378 K, corresponding to an X6R designation in the Electronic Industry Alliance codes.

High-symmetry transition-metal dichalcogenides (TMDs) have garnered substantial attention in the fields of sensors, optoelectronics, and valleytronics. However, the inherent C3 rotational symmetry of TMDs engenders highly isotropic properties, impeding their further technological progress. To overcome this limitation, we embarked on a study to investigate the effects of isotropic/anisotropic heterostructures engineering on WS2, aiming to break its C3 rotational symmetry. In this work, we designed and fabricated heterostructures composed of WS2 and ReS2 layers. Our comprehensive investigations revealed a remarkable emergence of anisotropic characteristics in excitons originating from the WS2 layers within the engineered WS2/ReS2 heterostructures. Moreover, we observed an enhancement in the valley polarizations of WS2 layers within the heterostructures, which is attributed to the reduced intervalley scattering facilitated by the WS2/ReS2 heterostructure configuration. This observation indicates the potential for leveraging heterostructure engineering to tailor and optimize anisotropic…

Understanding the thermal stability and degradation mechanism of β-Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) is crucial for their high-power electronics applications. This work examines the high temperature performance of the junctionless lateral β-Ga2O3 FinFET grown on a native β-Ga2O3 substrate, fabricated by metal-assisted chemical etching with Al2O3 gate oxide and Ti/Au gate metal. The thermal exposure effect on threshold voltage (Vth), subthreshold swing (SS), hysteresis, and specific on-resistance (Ron,sp), as a function of temperature up to 298 °C, is measured and analyzed. SS and Ron,sp increased with increasing temperatures, similar to the planar MOSFETs, while a more severe negative shift of Vth was observed for the high aspect-ratio FinFETs here. Despite employing a much thicker epilayer (∼2 μm) for the channel, the high temperature performance of Ion/Ioff ratios and SS of the FinFET in this work remains comparable to that of the planar β-Ga2O3 MOSFETs reported using epilayers ∼10–30× thinner. This work paves the way for further investigation into…

We present a compositional dependence study of electrical characteristics of AlxGa1−xN quantum well channel-based AlN/AlGaN/AlN high electron mobility transistors (HEMTs) with x=0.25,0.44, and 0.58. This ultra-wide bandgap heterostructure is a candidate for next-generation radio frequency and power electronics. The use of selectively regrown n-type GaN Ohmic contacts results in contact resistance that increases as the Al content of the channel increases. The DC HEMT device characteristics reveal that the maximum drain current densities progressively reduce from 280 to 30 to 1.7 mA/mm for x=0.25,0.44, and 0.58, respectively. This is accompanied by a simultaneous decrease (in magnitude) in threshold voltage from −5.2 to −4.9 to −2.4 V for the three HEMTs. This systematic experimental study of the effects of Al composition x on the transistor characteristics provides valuable insights for engineering AlGaN channel HEMTs on AlN for extreme electronics at high voltages and high temperatures.

In this study, we dry etched SiO2-masked (001) β-Ga2O3 substrates in HCl gas flow at a high temperature without plasma excitation. The etching was done selectively in window areas to form holes or trenches with inner sidewalls of (100) and/or {310} facets, which are the smallest surface-energy-density plane and oxygen-close-packed slip planes, respectively. In particular, (100) faceted sidewalls were flat and relatively close to the substrate surface normal. Therefore, this simple dry etching method is promising for fabricating plasma-damage-free trenches and fins used for β-Ga2O3-based power devices.

High power vertical GaN devices are in great demand recently due to their potential on extremely high-power conversion efficiency. Here, we show vertical GaN p–n power diodes fabricated on bulk GaN substrates with an optimized guard ring structure for electrical field management and high breakdown voltage. By using a low doped (∼1015 cm−3) 28 μm thick drift layer in combination with optimized ohmic contacts, a breakdown voltage (VB) of 4.9 kV and a low specific on-resistance (RON) of 0.9 mΩ cm2 were achieved. In combination with the high breakdown voltage and low specific on-resistance, the device demonstrated a Baliga figure of merit (V2B/RON) of 27 GW/cm2.

Progress in hardware and algorithms for artificial intelligence (AI) has ushered in large machine learning models and various applications impacting our everyday lives. However, today's AI, mainly artificial neural networks, still cannot compete with human brains because of two major issues: the high energy consumption of the hardware running AI models and the lack of ability to generalize knowledge and self-adapt to changes. Neuromorphic systems built upon emerging devices, for instance, memristors, provide a promising path to address these issues. Although innovative memristor devices and circuit designs have been proposed for neuromorphic computing and applied to different proof-of-concept applications, there is still a long way to go to build large-scale low-power memristor-based neuromorphic systems that can bridge the gap between AI and biological brains. This Perspective summarizes the progress and challenges from memristor devices to neuromorphic systems and proposes possible directions for neuromorphic system implementation based on memristive devices.

We report on the design and operation of a laser, which outputs wavelengths in the 1.2 and 1.5 μm ranges by leveraging two non-linear processes of stimulated Raman scattering and stimulated Brillouin scattering in diamond. By precisely controlling characteristics of the laser resonator formed around the diamond crystal, we are able to selectively control the onset of each non-linear process so as to tailor laser output characteristics both in way of wavelength and output power. This work demonstrates the high degree of flexibility and power-handling capacity of diamond for wavelength conversion of common laser wavelengths (such as 1064 nm as used in this work) and the generation of a span of discrete wavelengths (with up to eight cascaded orders being demonstrated in this work).

We report the incorporation of an ensemble of G centers in silicon-on-insulator (SOI) microrings using ion implantation and conventional nanofabrication. The coupling between the emitters and the resonant modes of the microrings is studied using continuous-wave and time-resolved microphotoluminescence (PL) experiments. We observe the resonant modes of the microrings on PL spectra, on the wide spectral range that is covered by G center emission. By finely tuning the size of the microrings, we match their zero-phonon line at 1278 nm with a resonant mode of quality factor around 3000 and volume 7.2 (λ/n)3. The zero-phonon line intensity is enhanced by a factor of 5, both in continuous-wave and time-resolved measurements. This is attributed to the Purcell enhancement of zero-phonon spontaneous emission into the resonant mode and quantitatively understood considering the distribution of the G center dipoles. Despite the enhancement of the zero-phonon emission, we do not observe any sizeable decrease in the average lifetime of the G centers, which points at a low radiative yield (<10%).…