The self-assembling of nanovoids with a precisely controlled depth at the GaN/GaAs interface is reported and their formation mechanism discussed. During the very early stages of GaN growth by molecular beam epitaxy over GaAs(100) misoriented substrates, nano-pits are formed by chemical reactions of gallium and nitrogen with a GaAs sacrificial layer. The GaAs sacrificial layer is grown on top of a GaAs/AlGaAs

Propagation of threading screw dislocations (TSDs) during hybrid growth, combined with TSD conversion by solution growth and bulk growth by physical vapor transport, has been investigated for 4° off and 15° off ##IMG## [http://ej.iop.org/images/1882-0786/14/8/085506/apexac15c1ieqn1.gif] {$\left(000\overline{1}\right)$} C-face seeds. The converted defects on basal planes (BP-defects) are able to be

In this study, we investigated the relationship of light output power with the optical thickness of the p-layers in AlGaN-based deep ultraviolet light-emitting diodes with a transparent high-Al-composition p-AlGaN clad layer, a thin p-GaN contact layer, and a reflective p-type electrode. By adjusting the thickness of the transparent high-Al-composition p-AlGaN clad layer, we observed a marked change

Conventional multijunction photovoltaic cells used for optical wireless power transmission, often referred to as laser power converters, currently involve a serious problem. The conversion efficiency lowers under temperature variation more notably than that of single-junction cells, because of changing absorption coefficient and resultant current mismatching among the subcells. Light-trapping using

Temporal focusing (TF) microscopy has a trade-off between temporal resolution, optical sectioning capability, and field of view. To improve this trade-off, we demonstrate time-multiplexed multi-line temporal focusing (TM-ML-TF) microscopy, which combines the time-multiplexed TF technique with multi-line focusing using a digital micromirror device. Compared with those for TF microscopy, the optical

The coercivity ( H c ) of nanocrystalline Nd–Fe–B magnet was simulated by multi-grain models in combination with hybrid Monte Carlo method. The simulated grain size dependence of H c with grain boundary (GB) model reproduces the available experiment nicely. The H c of direct contact (DC) model increase with the decreasing grain size ( S G ). This fact suggests that the H c of Nd–Fe–B magnets can be

To achieve asymmetric acoustic beam shaping, we propose a type of sub-wavelength meta-atom with mode-selective feature to construct the binary metasurfaces. Two coding bits, a rectangular cavity and a waveguide with seven Helmholtz resonators, are adopted to construct the meta-atom with an asymmetric transmission (AT) feature. By adopting different coding sequences, three types of asymmetric beam shaping

We demonstrate a 2792.0 nm passively Q-switched Er 3+ -doped fluoride fiber laser using a graphene saturable absorber mirror (GSAM). Through optimizing the cavity design and the parameters of the GSAM, stable pulses are obtained with a repetition frequency ranging from 60.2 to 221.8 kHz. The shortest pulse duration is 238.2 ns, which, to the best of our knowledge, is the shortest passively Q-switching

The strong coupling between the exciton polariton and the plasmon polariton produced by the interaction of light and matter forms a new hybrid polariton. We investigated the interaction between black phosphorus and metal generated polaritons. The spectrum with angular resolution as a variable shows anti-crossing characteristics in the strong coupling region. The proposed structure can achieve 65–150 meV

Photoluminescence (PL) and scintillation properties of GaN film deposited on Al 2 O 3 substrate were evaluated. In PL and X-ray induced scintillation spectra, two emission bands at 400 and 550 nm were observed. The X-ray induced scintillation decay curve demonstrated two decay components of 1.6 and 8.4 ns. Upon 55 Fe 5.9 keV X-ray and 241 Am 5.5 MeV α -ray excitation, the GaN film showed a higher scintilaltion

We theoretically propose a high-resolution biomolecules mass sensor based on a spinning resonator with a coherent phonon pump. When the resonator spins along the clockwise and counterclockwise directions, the resonator undergoes a different Sagnac effect, which combines the phonon pump with tunable amplitude and phase results in significantly enhanced probe transmission. If the mass of external biomolecules

High wall-plug efficiency (WPE) micro-light-emitting diodes with metalorganic chemical vapor deposition-grown tunnel junction (TJ) contacts are demonstrated. By employing chemical treatments before sidewall activation, the 20 × 20 μ m 2 TJ devices resulted in a voltage penalty of 0.2 V at 20 A cm −2 , compared to devices with indium-tin oxide (ITO) contacts. Moreover, the enhancement in light output

We report the structural and magnetic properties of Fe-doped InAs quantum dots (QDs) grown on GaAs (001) substrates by molecular beam epitaxy. The size and distribution of the QDs are revealed by atomic force microscopy and characterized by scanning tunnelling electron microscopy, which confirms zinc-blende crystal structure. Magnetometry measurements show the presence of ferromagnetism in the QDs

Bonding characters, such as length and strength, are of key importance for material structure and properties. Here, a machine learning (ML) model is used to predict the bonding properties from information pertaining to isolated systems before bonding. This model employs the density of states (DOS) before bond formation as the ML descriptor and accurately predicts the binding energy, bond distance,

Organic multivalued logic circuits (OMVLs) have drawn tremendous attention due to their high data processability and simple fabrication techniques. However, OMVLs have so far been achieved only on rigid silicon substrates, and this limits their potential for broader applications. In this study, we develop an organic ternary inverter on plastic substrates. The inverters showed well-balanced ternary

Chalcopyrite CuFeS 2 can be considered a promising thermoelectric material when its lattice thermal conductivity κ lat is successfully reduced. We attempted to obtain fine microstructures of Zn-doped CuFeS 2 to reduce κ lat while keeping its high power factor. A submicron scale grain size was achieved, and κ lat was reduced by 47%, though the electrical resistivity was significantly increased. According

We report the modulation of electrical properties of charge-ordered YbFe 2 O 4 films using electrostatic carrier doping. By utilizing the current switching effect under a high DC electric field as a probe, we detected the charge-ordered phase in the c -axis-oriented YbFe 2 O 4 films grown by pulsed-laser deposition. A three-terminal electric double-layer device with a thin channel of YbFe 2 O 4 and

We report a 1.8 times improved light extraction efficiency for truncated cone AlGaN DUV (275 nm emission) micropixel LEDs when the pixel size was reduced from 90 to5 μ m. This is a direct consequence of reducing the re-absorption of sideways-travelling photons, as the lateral absorption length was measured to be15 μ m using cathodoluminescence. We also investigated the effect of an Al 2 O 3 /Al sidewall

We investigate peculiar Bloch oscillations and interminiband Zener tunneling in a GaAs-based narrow-minigap superlattice up to room temperature, by using terahertz emission spectroscopy under dc bias electric fields. The Bloch oscillations observed previously with a π /2 phase shift at 10 K under relatively low bias fields are found to survive even at 300 K, where thermal energy kT exceeds the relevant

The role of edge termination is theoretically studied for the growth direction selectivity in chemical vapor deposition of graphene heterostructures with hexagonal boron nitride. It is found that the graphene island with hydrogen-free edge and the hexagonal boron nitride island with hydrogen-terminated edge induces the lateral and the vertical growth of the heterostructures we have experimentally observed

The polarity tuning of AlN films via introducing a period of trace oxygen supply in the initial sputtering process was demonstrated. High-temperature annealing was further implemented to improve the crystal quality of AlN. High-quality pure N-polar AlN film could be achieved by sputtering with pure N 2 gas. When trace oxygen was intentionally inputted in the sputtering chamber and its supply time surpassed

Thulium doped gallium oxides (Tm-Ga 2 O 3 ) films were deposited on Si substrates by the pulsed laser deposition method. Blue emissions (476 nm and 460 nm) can be observed by the naked eye from Tm-Ga 2 O 3 /Si light emitting diodes (LEDs). The threshold voltage of Tm-Ga 2 O 3 /Si LEDs is 6.3 V, which is lower than that of Tm-GaN/Si devices. By combining our previously reported green emission from Er-Ga

The interface properties of GaN metal–insulator–semiconductor (MIS) structures with a gate electrode metal deposited by electron beam (EB) or resistive heating evaporation were investigated. Also, the impact of the interface properties on the channel mobility in GaN MIS field-effect transistors was investigated. It was confirmed that interface charges including both interface states and positive fixed

Here, we show that whispering gallery modes of subwavelength dielectric resonators can exhibit ultrahigh electric and magnetic field enhancements due to their high-quality factors. The resonators are dielectric disks. The field enhancements are dependent on the height of the disk, the refractive index n and the azimuthal mode index, and they can reach ∼10 2 inside a subwavelength disk of n = 3.5. For

A thin-film narrowband retroreflector is proposed for a diverging free-space wave. The retroreflector consists of a focusing grating coupler in a waveguide resonator on a reflective substrate. The retroreflector is designed and fabricated for an incident wave diverging froma5.25 μ m diameter spot. The retroreflector gives a reflection towards the divergence point of the incident wave at the resonance

Non-negative matrix factorization (NMF) has been frequently used in research on live cells, biomolecules, and tissues (bio-Raman research) to disentangle the complicated and large sized data. A stagnation is that NMF does not provide unique decomposition, depending on initial settings; that is, NMF returns non-negative spectral components close to the truths, but solely giving several possibilities

We reduced the operating voltage of AlGaN homojunction tunnel junction (TJ) deep-ultraviolet (UV) light-emitting diodes (LEDs) by two approaches: the suppression of carbon incorporation and the doping of a high concentration of silicon in an n + -AlGaN layer. The AlGaN homojunction TJ deep-UV LEDs had a significantly reduced forward voltage upon suppressing the incorporation of carbon in the n + -AlGaN

We report uniaxially oriented nickel aluminum (NiAl) films grown by DC magnetron sputtering under in situ heating. The films self-organize in (110) orientation with relatively low surface roughness and tight grain boundaries in columnar structure. The electrical carrier concentration and resistivity are on the order of 10 21 cm −3 and 10 −5 Ω · cm, respectively. The plasmonic performance, as indicated

Terahertz flat optics based on our originally developed low-reflection metasurface with a high refractive index can offer attractive two-dimensional optical components for the manipulation of terahertz waves. However, it remains to be shown whether a planar collimating metalens made with our original metasurface could be mounted on a resonant tunneling diode with a short distance. Here, we demonstrate

Fano resonance is observed by the quantum interference between the discrete exciton-polariton state and continuous second-harmonic generation (SHG) in ZnO microrods. Due to the exciton component, the line shape of the SHG is changed by the coupling between the exciton-polariton and the SHG. When the asymmetry factor q of Fano line shape is several orders larger than the unit, the occupation of polariton

We propose a longitudinal Ramsey spectroscopy of atoms in a moving optical lattice. Spatially separated magnetic fields, which open the forbidden ##IMG## [http://ej.iop.org/images/1882-0786/14/7/072006/apexac0e16ieqn1.gif] {${}^{1}{S}_{0}-{}^{3}{P}_{0}$} transition by mixing with the dipole-allowed states, create Ramsey pulses for a probe laser introduced along the optical lattice. Excitation of atoms

We report the demonstration of p-NiO layers as junction termination extensions (JTEs) for realizing high-performance GaN power devices. The p-NiO was deposited by RF sputtering, a flexible process which enables to achieve high hole densities. In this work, we investigated the material and transport properties of p-NiO on GaN, and demonstrated its application as JTEs for GaN-on-Si Schottky barrier diodes

Weyl semimetals, which are a class of materials, have attracted extensive attention in condensed matter physics. In this letter, we report one-dimensional layered sonic crystals that exhibit many exotic properties. Based on our simulations, the results show that the synthetic Weyl points and their reflection phase have a vortex structure in this acoustic system. The nontrivial interface states, accompanying

The heat transport in a laterally configured nano-spintronic device, including a magnetic multi-layered nanowire has been investigated by detecting the second harmonic voltages. We show that the magnetic-field dependence of the second harmonic voltage in the multi-layered wire shows a clear spin-valve-like effect with the magnitude larger than the electrical spin valve effect. The second harmonic signal

We utilized phase-shifting electron holography on organic light emitting diodes consisting of N , N ′-di-[(1-naphthyl)- N , N ′-diphenyl]-(1,1′-biphenyl)-4,4′-diamine ( α -NPD) and tris-(8-hydroxyquinoline)aluminum (Alq 3 ) layers to visualize their built-in potential distribution. The bilayer showed three different electric fields, namely, the fields in the α -NPD layer, near the α -NPD/Alq 3 interface

In this study, the room-temperature pulsed operation of a nitride nanowire-based multi-quantum shell laser diode with a thick p-type GaN cap layer grown on a conventional c -face GaN substrate was demonstrated using the metalorganic chemical vapor phase epitaxy method. The threshold current density of the laser was approximately 62 kA cm −2 , and the voltage at the threshold current was 14 V. Optical

A novel steep-slope field-effect-transistor is proposed to break the thermionic limit by using the intrinsic isolated states in materials. The monolayer C 31 is used as the injection source to self-filter out high-energy electrons and strain engineering is adopted to modulate the energy gap and IS width. It is found that, under 8% biaxial tensile strain, the calculated subthreshold swing is as low

The shock premelting and spallation of single crystal copper under cylindrical converging impact are studied using molecular dynamics simulations. For the axis of a cylindrical potential wall along the [001] crystallographic direction, the anisotropy of shock response is very obvious at the shock strength 1.4 km s −1 . Premelting occurs at the wavefront in the 〈110〉 direction, but not in the 〈100〉

Improvement of light extraction efficiency of deep ultraviolet light-emitting-diodes (DUV-LEDs) was obtained by adopting a Ni/Al reflective electrode. Optical reflectivity up to 78.1% at 277 nm was achieved. The enhanced reflectivity after thermal annealing was ascribed to the formation of Ni clusters embedded inside the Al matrix as revealed by the correlation between the surface morphology and chemical

A nearly-ideal edge termination for GaN p–n junctions was designed and demonstrated using Mg-ions implanted field limiting rings (FLRs). The FLRs were fabricated via the ultra-high-pressure annealing process after implanting Mg-ions into the etched n-type region outside the main p–n junction. The results of the technology computer-aided design simulation indicate that by optimizing the space and width

The critical shear stress (CSS) of gold nanocontacts (NCs) was estimated using a home-made in situ transmission electron microscopy holder equipped with a quartz length-extension resonator (LER) as a force sensor. The LER was being oscillated at its resonance frequency utilizing frequency modulation method, enabled us to measure the dissipative energy in the NCs. From the LER amplitude dependence of

Due to their unique photoelectric properties, two-dimensional (2D) semiconductors have recently attracted much attention as active elements in optoelectronic devices. However, the effectiveness of such devices is limited by the high transparency of 2D semiconductor films, which leads to a photosensitivity decrease. An increase in the electric field due to the local plasmons excitation is a widely used

In this work, anatase N-doped TiO 2 was prepared by a facile pre-sintering method. The usage of N-doped TiO 2 not only improved the electrical performance of the electron transport layer, but prevented high-temperature sintering of the substrate. As a result, the devices with N-doped TiO 2 exhibited higher average power conversion efficiency of 16.65%. Furthermore, N-doped TiO 2 was used in flexible

The impact of sulfur doping on broadband terahertz emission in GaSe single crystals was investigated by optical rectification with oo-o phase matching. The maximum peak value of THz radiation generated from S-doped 2.5 mass% GaSe is 28.3% larger than that of intrinsic GaSe with pump fluence of 637 mW cm −2 and azimuthal angle of 0 o . The saturation of THz emission in S-doped 2.5 mass% GaSe is increased

By reducing the noise component induced by the amplitude-to-phase conversion, a broadband phase-noise suppression of a 20.5 GHz photonic microwave, generated from an optical heterodyne of a dual-wavelength single-frequency fiber laser (DW-SFFL) is experimentally demonstrated. This is done by suppressing the intensity noise of the DW-SFFL through optoelectronic feedback, the microwave shows phase-noise

In this paper, a single-layer ultrawideband polarization conversion metasurface with high-efficiency is proposed. The top metallic structure is formed by folding the L-shaped structure in meanders, which can produce additional resonances and reduce the resonant frequency. Therefore, ultrawideband polarization conversion is realized (ranging from 7.79 to 30.22 GHz, covering C-, X-, Ku-, K-, and Ka-bands)

Metal-oxide-semiconductor capacitors with HfO 2 /1-monolayer TiO 2 /SiO 2 stacks were examined to explore the origin of the interface dipole modulation. The capacitance–voltage ( C–V ) measurements exhibited that the polarity of the interface dipole layer changes depending on the gate bias. The hard X-ray photoelectron spectroscopy measurements demonstrated that an applied gate voltage induces small

We report that the superconducting critical magnetic field can be nonreciprocal under a bias of an electric current in a superconducting [Nb/V/Ta] n superlattice without a center of inversion. The critical magnetic field showed a clear difference between positive and negative magnetic fields. Furthermore, the magnitude relation between the positive and negative critical magnetic fields is reversed

We report on the first demonstration of metalorganic vapor phase epitaxy-regrown (MOVPE) ohmic contacts in an all MOVPE-grown β -Ga 2 O 3 metal semiconductor field effect transistor (MESFET). The low-temperature (600 °C) heavy (n + ) Si-doped regrown layers exhibit extremely high conductivity with a sheet resistance of 73 Ω/□ and a record low metal/n + -Ga 2 O 3 contact resistance of 80 mΩ·mm and specific

We demonstrate backscattering X-ray imaging using a Fresnel zone aperture (FZA), where the line width of the outermost circle is100 μ m. The method is a lensless imaging technique employing an optical aperture instead of a lens. We successfully reconstructed test objects from four images observed using a series of FZAs without an iterative procedure during the reconstruction process. We also confirmed

The combined effect of the mass and stiffness on a double-layered microcantilever has been studied. The resonance frequency of a silicon microcantilever with thin nickel film deposited on top is monitored as a function of the film thickness and examined based on a bi-layer cantilever model. These reveal that both mass and stiffness of the top layer on the cantilever structure affect the rate of the

We apply a surface thermal fluctuation spectroscopy technique to investigate the liquid nature of ionic liquid (IL) thin films and micro-droplets. While the spectrum for bulk IL was well explained by a simple Newtonian fluid model, a significant contribution of viscoelasticity was suggested for the vacuum-deposited thin films and micro-droplets. For a sample of IL micro-droplets with statistical distributions

We design a supermolecular structure composed of two identical scatterers with opposite orientations in air. By adjusting the interval between them and rotating them, topological phase transitions occur. The combination of rotational and translational operations provides us with wide scope of interface states and multiple-choice to achieve interface states. Therefore, the interface states must exist

We present a general synthesis of transition metal difluorides (TMF 2 )–carbon nanocomposite films by magnetron co-sputtering the Fe/Co and polytetrafluoroethylene (Teflon) targets. The composites consist of binary TMF 2 (TM = Fe, Co) nanoparticles with a crystallite size of ∼8 nm immersed in a carbon matrix. The antiferromagnetic nature of TMF 2 nanoparticles with the Néel temperature T N of 40 K

Low-density electronic states in the energy gap of an amorphous In–Ga–Zn–O film control device performance. Herein, density of states (DOS) distribution from valence band to the in-gap states of 10 14 cm −3 eV −1 level was determined using high-sensitivity UV photoemission spectroscopy. Exponential tail states accompanying two energetically-localized states were directly observed as reported previously

In this study, switching of the spin-wave propagation was investigated using an yttrium iron garnet (YIG) waveguide. A dynamic magnonic crystal (DMC) was designed to control the non-reciprocal surface spin waves. The DMC controlled the periodic modulation field on the YIG film and caused a strong Bragg reflection on the surface spin waves. The maximum effect of Bragg reflection was analyzed by the

Photochromic diarylethenes that are reversibly isomerized by visible and ultraviolet light irradiation could be had the potential to be utilized in a variety of functional devices and systems. In this study, we observed the autonomous formation of a sharp, nanometer-scale boundary between two different surface morphology of photochromic diarylethene crystals when both visible and ultraviolet light

We report a highly efficient blue thermally activated delayed fluorescence (TADF) emitter, namely, MCz-TXO. MCz-TXO exhibits close energy level matching of the three states: charge transfer (CT) and locally excited triplet states, and a CT singlet state. Owing to the good energy level matching and heavy atom effect of sulfur in the molecular structure, MCz-TXO shows very large experimental rate constant

A simple measurement technique is proposed for multi-pitched grating inserted in an external cavity diode laser. Measuring grating rotation and variation of multiple resonant wavelengths enables us to estimate grating periods and Littrow angles simultaneously. We experimentally determined that sufficient variation of resonant wavelength (i.e. ∼1.6 nm) could be obtained even with a grating rotation

A multi-wavelength compact ultrafast laser based on a single-mode waveguide inscribed in Nd:YAG and graphene saturable absorber is developed. By changing the pump parameters, we demonstrate single-, dual- and multi- wavelength mode-locking regimes. Accurate control of intracavity losses provides stable CW passive mode-locking at a wavelength of 1064 nm and dual-wavelength mode-locking at 1061 and 1064 nm