Demonstration of 651†nm InGaN-based red light-emitting diode with an external quantum efficiency over 6% by InGaN/AlN strain release interlayer.

This work reports a high-performance InGaN-based red-emitting LED with a strain-release interlayer (SRI) consisting of an InGaN stress-release layer (SRL) and an AlN dislocation confinement layer (DCL) in unintentionally doped GaN (u-GaN). The SRL introduces a tensile strain which could decrease the in-plane compressive stress of the u-GaN layer, while the DCL could reduce the dislocation density and thus improve the crystal quality of the u-GaN layer. Consequently, a high-efficiency InGaN-based red-emitting LED with a peak wavelength of 651 nm and an external quantum efficiency of 6.04% is realized. In addition, the room-temperature photoluminescence (PL) mapping emission wavelength is uniform across a 4-inch wafer with a standard deviation of 3.3 nm. Therefore, the proposed SRI offers good potential for mass-producing high-performance and long-wavelength InGaN-based red-emitting LEDs.

Self-powered asymmetric metal-semiconductor-metal AlN deep ultraviolet detector.

Self-powered ultraviolet detectors may find application in aviation and military fields. Here we demonstrate a self-powered asymmetric metal-semiconductor-metal (MSM) deep ultraviolet (DUV) detector with an Ni/Al electrode contact to AlN, and a photoelectric response current increase from dark current (Id) 2.6 × 10-12 A to 1.0 × 10-10 A after UV illumination (Ip) at 0 V bias. To further improve device performance, trenches are etched in AlN, and the Ni/Al electrodes are deposited in trenches to form a three-dimensional MSM (3D-MSM) structure. The improved performance is attributed to the stronger electric field from the asymmetric electrode and a shorter carrier migration path from the 3D-MSM device configuration. Our work will promote the development and application of DUV self-powered devices.

Unidirectional-emitting GaN-based micro-LED for 3D display.

Naked-eye 3D micro-LED display combines the 3D characteristics and advantages of micro-LED simultaneously. A conventional micro-LED device emission exhibits Lambertian distribution, and it requires stacking of multiple optical components into a 3D display, resulting in bulky systems, low efficiency, and a limited viewing zone and points. We propose and investigate a single-chip micro-LED with unidirectional emission through an in-situ integrated resonant cavity and metasurface, which has great potential to be used for an efficient naked-eye 3D display with a wide viewing angle and multiple viewpoints. This Letter promotes the application of GaN-based micro-LEDs in a display, especially a 3D display.

Circularly polarized light emission from a GaN micro-LED integrated with functional metasurfaces for 3D display.

This Letter proposes a circularly polarized (CP) light GaN micro-LED which is integrated with functional metasurfaces. The one-dimensional metallic nanograting can achieve a high transverse electric (TE) reflectivity (${{\rm{R}}_{\rm{TE}}}$) and extinction ratio (ER) of TE and transverse magnetic (TM) waves, which is highly polarized output for micro-LEDs. Besides, the nanograting, which is integrated on the bottom of the GaN layer, can also support a resonant cavity, together with the top distributed Bragg reflector, which can shape the radiation pattern. By optimizing the structure parameters of nanograting, the ${{\rm{R}}_{\rm{TE}}}$ achieves over 80%, and the ER reaches higher than 38 dB at 450 nm for the GaN micro-LED. Additionally, the metasurface, which acts as a quarter-wave plate, was investigated to control the phase delay between the polarization state of the electric wave in two orthogonal components. Finally, the circular shape of the transmitted pattern denotes the high performance of the metasurface which is integrated in the micro-LED for CP light emission. The work reported in this Letter might provide potential application in a 3D polarized light display.

Understanding homoepitaxial growth of horizontal kinked GaN nanowires.

Epitaxial horizontal nanowires (NWs) have attracted much attention due to their easily large-scale integration. From the reported literature, epitaxial growth is usually driven by minimization of strain between NW and substrate, which governs the growth along with specific crystallographic orientation. Here, we report the first homoepitaxial growth of horizontal GaN NWs from a surface-directed vapor-liquid-solid growth method. The NWs grow along with six symmetry-equivalent 〈1-100〉 (m-axis) directions, exhibiting a random 60°/120° kinked configuration. Owing to homoepitaxial growth, strain could be eliminated. From the obtained results, we suggest that the formation the horizontal NWs, and their growth direction /orientation is not directly related to the strain minimization. A general rule based on the epitaxial relationship and potential low-index growth orientation is proposed for understanding the arrangement of epitaxial horizontal NWs. It is deduced that kinking of the horizontal NWs was attributed to unintentional guided growth determined by the roughness of the substrates' surface. This study provides an insight for a better understanding of the evolution of epitaxial horizontal NWs, especially for the growth direction/orientation.

Multiplexing multifoci optical metasurfaces for information encoding in the ultraviolet spectrum.

Recently, optical metasurfaces have attracted much attention due to their versatile features in manipulating phase, polarization, and amplitude of both reflected and transmitted light. Because it controls over four degrees of freedom: phase, polarization, amplitude, and wavelength of light wavefronts, optical cryptography is a promising technology in information security. So far, information encoding can be implemented by the metasurface in one-dimensional (1D) mode (either wavelength or polarization) and in a two-dimensional (2D) mode of both wavelength and polarization. Here, we demonstrate multiplexing multifoci optical metasurfaces for information encoding in the ultraviolet spectrum both in the 1D and 2D modes in the spatial zone, composed of high-aspect-ratio aluminum nitride nanorods, which introduce discontinuous phases through the Pancharatnam-Berry phase to realize multifoci in the spatial zone. Since the multiplexed multifocal optical metasurfaces are sensitive to the helicity of the incident light and the wavelength is within the ultraviolet spectrum, the security of the information encrypted by it would be guaranteed.

Pixel crosstalk in naked-eye micro-LED 3D display.

Micro-LED display is considered to be the most promising display technology, and naked-eye 3D display represents the most advanced frontier of display. Naked-eye 3D micro-LED display has both the advantages of micro-LED display and the characteristics of naked-eye 3D display. Only conceptual solutions for 3D micro-LED display have been reported so far. The effect of luminescence distribution and the direction of micro-LED devices on crosstalk in the naked-eye 3D display is not clear. In this paper, we first investigated the chip-shaping effect on the emission characteristics, mainly the luminescence distribution and direction of the micro-LED, and then we investigated the influence of luminescence distribution and direction of micro-LED on the pixel crosstalk in naked-eye micro-LEDs 3D display. Our work should advance the micro-LED display, especially the micro-LED 3D display.

Sputtering AlN/InxAl1-xN distributed Bragg reflector across the full visible range on Si and SiO2 substrates.

III-nitride-based distributed Bragg reflectors (DBRs) are advantageous in being in-situ integrated in III-nitride devices, and the bandgaps and their other corresponding optical parameters are tunable. However, a growing nitride DBR with low strain and high reflectivity remains a challenge. Here we demonstrate an AlN/InxAl1-xN DBR grown on Si and SiO2 substrates by reactive radio-frequency magnetron sputtering. Reflectance wavelengths covering the whole visible regions of the visible spectrum were achieved by rationally tuning the indium composition in InxAl1-xN and each layer's thickness of an AlN/InxAl1-xN DBR. This Letter should advance the design and fabrication of nitride optical and optoelectrical devices by incorporating an AlN/InxAl1-xN DBR, such as vertical-cavity surface-emitting laser (VCSEL) and RC LEDs.

Ultrawide bandgap AlN metasurfaces for ultraviolet focusing and routing.

All-dielectric metasurfaces offer a promising way to control amplitude, polarization, and phase of light. However, ultraviolet (UV) component metasurfaces are rarely reported due to significant absorption loss for most dielectric materials and the required smaller footprint or feature size. Here, we demonstrate broadband UV focusing and routing in both transmission and reflection modes in simulations by adopting aluminum nitride (AlN) with ultrawide bandgap and a waveplate metasurface structure. As for experiments, the on-axis, off-axis focusing characteristics in transmission mode have been investigated at representative UVA (375 nm) wavelength for the first time, to the best of our knowledge. Furthermore, we fabricated a UV transmission router for monowavelength, guiding UV light to the designated different spatial positions of the same or different focal planes. Our work is meaningful for the development of UV photonics components and devices and would facilitate the integration and miniaturization of UV nanophotonics.

Three-dimensional metal-semiconductor-metal AlN deep-ultraviolet detector.

Conventional metal-semiconductor-metal (MSM) ultraviolet (UV) detectors have the disadvantage of limited adjustable structural parameters, finite electrical field, and long carrier path. In this Letter, we demonstrate a three-dimensional (3D) MSM structural AlN-based deep-UV (DUV) detector, fabricated through simple trench etching and metal deposition, while flip bonding to the silicon substrate forms a flip-chip 3D-MSM (FC-3DMSM) device. 3D-MSM devices exhibit improved responsiveness and response speed, compared with conventional MSM devices. Time-dependent photoresponse of all devices is also investigated here. The enhanced performance of the 3D-MSM device is to be attributed to the intensified electrical field from the 3D metal electrode configuration and the inhibition of the carrier vertical transport, which unambiguously increases the carrier collection efficiency and migration speed, and thus the responsivity and speed as well. This work should advance the design and fabrication of AlN-based DUV detectors.

Crystal phase evolution in kinked GaN nanowires.

Seed-catalysed growth has been proved to be an ideal method to selectively tune the crystal structure of III-V nanowires along its growth axis. However, few results on relevant nitride NWs have been reported. In this study, we demonstrate the growth of epitaxial kinked wurtzite (WZ)/zinc-blende (ZB) heterostructure GaN NW arrays under the oxygen rich condition using hydride vapour-liquid-solid vapour phase epitaxy (VLS-HVPE). The typical GaN crystal includes WZ and ZB phases throughout the whole NW structure. A detailed structural analysis indicates that a stacking faults free zone was occasionally observed near the NW tips and in the relatively long kinked 〈11-23〉 directions segments (>200 nm). Furthermore, some NWs (<5%) develop phase boundaries, resulting in kinking and crystal phase evolution. A layer-by-layer growth mode was proposed to explain the crystal phase evolution along the phase boundaries. This study provides new insights into the controlled growth of wurtzite (WZ)/zinc-blende (ZB) heterostructure GaN NW.

Design of AlN ultraviolet metasurface for single-/multi-plane holography.

The metasurface promises an unprecedented way for manipulating wavefronts and has strengths in large information capacity for the hologram. However, strong absorption loss for most dielectric materials hinders the realization of such a metasurface operating in the ultraviolet (UV) spectrum. Herein, aluminum nitride (AlN) with an ultrawide bandgap has been utilized as the material of the UV metasurface for multi-plane holography, increasing the information capacity and security level of information storage simultaneously. The metasurface for multi-plane holography achieving a correlation coefficient of over 0.8 with three reconstructed images has been investigated, and also the single-plane holography at an efficiency of 34.05%. Our work might provide potential application in UV nanophotonics.

Exploring how Chinese adults living with spinal cord injury viewed the prospect of inpatient peer support programs within a hospital-based rehabilitation setting.

STUDY DESIGN: Generic qualitative design. OBJECTIVES: To explore how Chinese adults living with spinal cord injury (SCI) viewed the prospect of inpatient peer support programs within a rehabilitation setting. SETTING: Hospital in China. METHODS: A purposive sample of adult inpatients with SCI (N = 6) currently undergoing rehabilitation was recruited. Each participant was interviewed twice. Twelve interview transcripts were analyzed using a thematic method. RESULTS: Five higher-order themes were developed. First, participants had unique backgrounds and personal lives before and after their SCI and reported frustrations about their lives resulting from their SCI. Second, participants reported varying degrees of satisfaction with their rehabilitation and identified the facilitators and barriers to their rehabilitation. Third, their perspectives on peer support were shaped by their rehabilitation goals. For example, participants who solely focused on the recovery of physical functioning noted that peers could help to supplement existing rehabilitation programming by guiding their rehabilitation exercises. Participants who concentrated on their future lives believed peers could teach them new skills to facilitate their integration in the community. However, some participants felt they could not trust peers' advice because peers are not healthcare providers. Fourth, peer support delivery options varied from online chat groups (i.e., WeChat), in-person conversations, and mentoring lectures. Finally, anticipated outcomes were related to obtaining practical and emotional support from peers, being motivated, and feeling understood. CONCLUSIONS: Participants harbored mixed views on potential use-value and necessity of hospital-based peer support programs, which could inform future utilization of SCI peer support within Chinese hospitals.

Simultaneously improve the luminous efficiency and color-rendering index of GaN-based white-light-emitting diodes using metal localized surface plasmon resonance.

With the penetration of semiconductor lighting, GaN-based white-light-emitting diodes (WLEDs) with a high color-rendering index (CRI) and simultaneous high luminous efficiency (LE) are required, especially for high-quality indoor lighting. Here, by adopting metal nanoparticles (Ag and Au NPs) into hybridized color conversion material composed of broadband LuAG:Ce phosphor and narrowband CdSe/ZnS red quantum dots, we have fabricated AgAu-WLEDs with simultaneously increased LE (12% increment at 40 A/cm2) and CRI (maximum of 94.5), and decreased correlated color temperature (CCT, from CCT=6000 K to = 4800 K), compared with WLEDs without metal NPs. This improved performance of WLEDs is ascribed to increased color conversion efficiency brought from localized surface plasmon resonance and thus a strong resonant light scattering effect from the incorporated metal NPs. We believe the approach reported in this work will find its application in GaN WLEDs, thus advancing the development of high-efficiency and quality semiconductor lighting.

Horizontal GaN nanowires grown on Si (111) substrate: the effect of catalyst migration and coalescence.

Here, we demonstrate the growth of horizontal GaN nanowires (NWs) on silicon (111) by a surface-directed vapor-liquid-solid growth. The influence of the Au/Ni catalysts migration and coalescence on the growth of the NWs has been systematically studied. 2D root-like branched NWs were gown spontaneously through catalyst migration. Furthermore, a novel phenomenon that a catalyst particle is embedded in a horizontal NW was observed and attributed the destruction of growth steady state due to the catalysts coalescence. The transmission electron microscopy and photoluminescence, cathodoluminescence measurement demonstrated that the horizontal NWs exhibit single crystalline structures and good optical properties. Our work sheds light on the horizontal NWs growth and should facilitate the development of highly integrated III-V nanodevices on silicon.

Multilevel Resistive Switching in P-N Heterostructure Memory.

High storage density is an important requirement for resistive random access memory (RRAM) devices. Multilevel resistive switching (RS) in RRAMs does not require much change to current technologies compared with device size reduction and 3D integration. Herein, five stable resistance states can be obtained in a Pt/p-NiO/n+-Si memory device by controlling the current compliance (CC). The RS mechanism can be attributed to the formation and rupture of localized conducting filaments (CFs) in an NiO film. The conductivity of the low resistance states (LRS) is determined through the combined action of the P-N junction and localized CFs. The CC can be used to effectively modulate the formation of localized CFs and junction resistance. Importantly, different LRS have large differences in resistance values, resulting in multilevel memory. A model is suggested and discussed to account for the observed multilevel memory operation.

Theoretical Analysis of Lattice-Mediated Plasmon Resonance Using Finite-Difference Time-Domain Method.

Although much progress has been made on lattice plasmon mode (LPM), there is still a lack of systematic studies on LPM generation; questions remain unanswered on topics such as high-order LPM generation, LPM generation from near-coupling complex elements, and modulation of incidence energy. Here, we systematically evaluated the properties of multiple high-order LPM, energy flow modulation of incident polarization, element, angle of incidence, and hybrid of dual lattice using the finite-difference time-domain method. This study presents a clear illustration of LPM and will help on further development of LPM and plasmonics-based fields.

A boron nitride electrode modified with a nanocomposite prepared from an ionic liquid and tungsten disulfide for voltammetric sensing of 4-aminophenol.

Boron nitride (BN) was used as a support and covered with an ionic liquid (IL) and tungsten disulfide (WS2) nanoparticles to obtain an electrode for the determination of 4-aminophenol (4-AP). BN was prepared using a "solvent cutting" method, and the BN-IL-WS2 nanocomposite was obtained by an ultrasonic method. BN and its hybrids were characterized by scanning electron microscopy, transmission electron microscopy and X-ray diffraction. When the BN-IL-WS2 composites were coated on the surface of the electrode, the response to 4-AP was strongly amplified due to the strong synergetic effect between the three materials. The voltammetric response of the modified sensor (with a maximum at 0.29 V vs. Ag/AgCl) in solutions with a pH of 6 is linear in the 0.01-50 µΜ 4-AP concentration range, and the limit of detection is 3 nM. A modified glassy carbon electrode was applied for the determination of 4-AP in seawater and dispersions containing paracetamol tablets. The results were consistent with those obtained by HPLC. Graphical abstract Schematic representation of the voltammetric determination process of 4-aminophenol (4-AP). The electrochemical sensor based on the glassy carbon electrode modified with boron nitride (BN), ionic liquid (IL) and tungsten disulfide (WS2) nanomaterials. They, exhibit an excellent performance compared with other electrodes.

Phosphorus Particles Embedded in Reduced Graphene Oxide Matrix to Enhance Capacity and Rate Capability for Capacitive Potassium-Ion Storage.

Early studies indicate that graphite is feasible as the negative electrode of a potassium-ion battery, but its electrochemical performance still cannot meet the demands of applications. More efforts should be focused on increasing the specific capacity and improving the rate capability in the meantime. Thus, stainless-steel autoclave technology has been utilized to prepare phosphorus nanoparticles encapsulated in reduced graphene oxide matrix as the electrode materials for a potassium-ion battery. As a result, the composite matrix affords high reversible capacities of 354 and 253 mA h g-1 at 100 and 500 mA g-1 , respectively. The superior electrochemical performance is mainly because the composite matrix possesses better electronic conductivity and a robust structure, which can promote the electron-transfer performance of the electrode. Furthermore, phosphorus particles can contribute to the high capacity through an alloying mechanism. In addition, the silklike, ultrathin, film composite with a high surface area is conducive to capacitive potassium-ion storage, which plays a more important role in rate performance and a high current density capability.

Fusion of Haptic and Gesture Sensors for Rehabilitation of Bimanual Coordination and Dexterous Manipulation.

Disabilities after neural injury, such as stroke, bring tremendous burden to patients, families and society. Besides the conventional constrained-induced training with a paretic arm, bilateral rehabilitation training involves both the ipsilateral and contralateral sides of the neural injury, fitting well with the fact that both arms are needed in common activities of daily living (ADLs), and can promote good functional recovery. In this work, the fusion of a gesture sensor and a haptic sensor with force feedback capabilities has enabled a bilateral rehabilitation training therapy. The Leap Motion gesture sensor detects the motion of the healthy hand, and the omega.7 device can detect and assist the paretic hand, according to the designed cooperative task paradigm, as much as needed, with active force feedback to accomplish the manipulation task. A virtual scenario has been built up, and the motion and force data facilitate instantaneous visual and audio feedback, as well as further analysis of the functional capabilities of the patient. This task-oriented bimanual training paradigm recruits the sensory, motor and cognitive aspects of the patient into one loop, encourages the active involvement of the patients into rehabilitation training, strengthens the cooperation of both the healthy and impaired hands, challenges the dexterous manipulation capability of the paretic hand, suits easy of use at home or centralized institutions and, thus, promises effective potentials for rehabilitation training.