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The growth of hexagonal boron nitride (h‐BN) and van der Waals (vdW) epitaxy of blue multi‐quantum well (MQW) GaN‐based LED heterostructures on 6‐inch sapphire substrates using metal‐organic chemical vapour deposition (MOCVD) is demonstrated. Challenges associated with the growth of large surface h‐BN and the subsequent vdW epitaxy of GaN‐based LED heterostructures are discussed. To overcome these challenges, the spatial uniformity is controlled of the growth temperature, optimizes the slope of temperature variations during the growth and cooling process, and manages the surface temperature during switching of gas flows. With these adaptations, high quality GaN‐based LED heterostructures are grown on h‐BN without any spontaneous delamination. The GaN‐based LED devices are then fabricated on a 6‐inch sapphire wafer, which are lifted off as a membrane and transferred to a flexible copper support. These GaN‐based LED devices emitt bright blue illumination with an electroluminescence peak at 437 nm. This scaling up of growth, lift‐off, and transfer can lead to the commercialization of GaN‐based LEDs on h‐BN template on 6‐inch sapphire substrates, with a process compatible with current modern equipment for the fabrication of LEDs and electronic devices. [ABSTRACT FROM AUTHOR]

Several technological challenges have prevented GaN‐based micro‐LEDs from finding application in mass market displays, despite their unique properties such as very high brightness and the very fast response time of GaN‐based materials. The primary challenges are the cost and complexity of lift‐off and transfer of LEDs from sapphire substrates to suitable supports as well as the lowered performance of tiny micro‐LEDs caused by chemical etching that defines individual LEDs. Herein, this work reports demonstration of a complete process that solves these challenges with epitaxy and cleanroom technologies that are commercially available. The process begins with van der Waals epitaxy of 2D h‐BN on silica masks with square, triangular and hexagonal patterns on sapphire substrates which define the micro‐LED regions. Then selective area growth of MQW LED heterostructures, with ultra smooth crystalline sidewalls, down to ultra tiny size of 1.4 µm is performed. Because of the lack of vertical chemical bonds in the h‐BN layer, simple mechanical lift‐off and transfer is performed on an array of LEDs heterostructures down to size of 8 µm. Finally, transparent ITO p‐contacts are deposited on LEDs with uniform lift‐off, resulting in high brightness LEDs. [ABSTRACT FROM AUTHOR]

We have previously surveyed a panel of 508 physicians from around the world about which biomarkers would be relevant if obtained in a very short time frame, corresponding to emergency situations (life-threatening or not). The biomarkers that emerged from this study were markers of cardiovascular disease: troponin, D-dimers, and brain natriuretic peptide (BNP). Cardiovascular disease is a group of disorders affecting the heart and blood vessels. At the intersection of medicine, basic research and engineering, biosensors that address the need for rapid biological analysis could find a place of choice in the hospital or primary care ecosystem. Rapid, reliable, and inexpensive analysis with a multi-marker approach, including machine learning analysis for patient risk analysis, could meet the demand of medical teams. The objective of this opinion review, proposed by a multidisciplinary team of experts (physicians, biologists, market access experts, and engineers), is to present cases where a rapid biological response is indeed valuable, to provide a short overview of current biosensor technologies for cardiac biomarkers designed for a short result time, and to discuss existing market access issues. [ABSTRACT FROM AUTHOR]

The van der Waals (vdW) epitaxy of three-dimensional (3D) device structures on two-dimensional (2D) layers is particularly interesting for III-nitrides because it may relax lattice matching and thermal mismatch requirements and can allow convenient lift-off of epilayers and optoelectronic devices. In this article, we report the vdW epitaxy of 3D GaN/AlGaN on 2D h-BN grown on a-, c-, and m-plane sapphire substrates via metal–organic chemical vapor phase epitaxy. First, we study 2D h-BN layers grown on a-, c-, and m-plane sapphire to demonstrate the effect of the substrate on h-BN growth and h-BN alignment. We find that h-BN can align itself to its preferred c-axis with a slight misorientation on the m-plane sapphire substrate. However, the differences in crystallographic orientation, thermal expansion coefficient, and surface energy of differently oriented sapphire substrates strongly influence the surface morphology (good for a- and c-planes) and the adhesion of h-BN layers (lift-off only possible for the c-plane). Second, the vdW growth of 3D GaN/AlGaN on 2D h-BN grown on a-, c-, and m-planes of sapphire was investigated. High-resolution X-ray diffraction (HR-XRD) 2θ–ω scan and selected area electron diffraction pattern were used to demonstrate the misorientation of GaN/AlGaN grown on 2D h-BN/m-plane sapphire compared to polar GaN grown on 2D h-BN/a- and c-plane sapphire. It was found that the morphology and crystalline quality of GaN/AlGaN are directly affected by the 2D h-BN layers. These results provide initial insight into the impact of substrate orientation, thereby acting as a guide for the potential design of III-nitride/h-BN vdW epitaxy seeking to use nonpolar or semipolar planes of sapphire for optoelectronic devices such as light-emitting diodes (LEDs), high-power electronics, and detectors. [ABSTRACT FROM AUTHOR]

GaN, with its wide bandgap of 3.4 eV, has emerged as an efficient material for designing high-efficiency betavoltaic batteries. An important part of designing efficient betavoltaic batteries involves a good understanding of the full process, from the behavior of the nuclear material and the creation of electron-hole pairs all the way through the collection of photo-generated carriers. This paper presents a detailed model based on Monte Carlo and Silvaco for a GaN-based betavoltaic battery device, modeled after Ni-63 as an energy source. The accuracy of the model is verified by comparing it with experimental values obtained for a GaN-based p-i-n structure under scanning electron microscope illumination. [ABSTRACT FROM AUTHOR]

We summarize our recent progress in Metal organic vapor phase epitaxy (MOVPE) van der Waals epitaxy of wafer-scale 2D layered hexagonal boron nitride (h-BN) on sapphire and subsequently grown III-N materials. This one step growth process allows for mechanical transfer of GaN-based devices from h-BN on sapphire to various supports. We first review the growth of h-BN on unpatterned and patterned sapphire templates. Second, we describe h-BN growth on dielectric pre-patterned sapphire templates, which enables dicing-free GaN-based device structures' pick-and-place heterogenous integration of III-N devices. Third, we review the growth of self-assembled 1D GaN-based nanowire light emitting diode (LED) structures on layered 2D h-BN for mechanical transfer of nanowire LEDs. Together, these results illustrate the potential of wafer-scale van der Waals h-BN MOVPE to enhance the III-N device functionality and to improve III-N processing technology. [ABSTRACT FROM AUTHOR]

We report an elongation of emission wavelength by inserting a ∼70 nm thick high quality semi-bulk (SB) In y Ga 1-y N buffer layer underneath the In x Ga 1-x N/In y Ga 1-y N (x > y) multi-quantum-well (MQW).While the MQW structure without the InGaN SB buffer is fully strained on the n-GaN template, the MQW structure with the buffer has ∼15% relaxation. This small relaxation along with slight compositional pulling induced well thickness increase of MQW is believed to be the reason for the red-shift of emission wavelength. In addition, the SB InGaN buffer acts as an electron reservoir and also helps to reduce the Quantum Confined Stark Effect (QCSE) and thus increase the emission intensity. In this way, by avoiding fully relaxed buffer induced material degradation, a longer emission wavelength can be achieved by just using InGaN SB buffer while keeping all other growth conditions the same as the reference structure. Thus, a reasonably thick fully strained or very little relaxed InGaN buffer, which is realized by “semi-bulk” approach to maintain good InGaN material quality, can be beneficial for realizing LEDs, grown on top of this buffer, emitting in the blue to cyan to green regime without using excess indium (In). [ABSTRACT FROM AUTHOR]

The effect of indium (In) in the barrier of InGaN/GaN multiple quantum well (MQW) has been studied for MQWs with and without semi-bulk InGaN buffer. From simulation, the optimum In content in the barrier with 3-5 nm width is 5-7% to get the optimal material quality and internal quantum efficiency (IQE) of ∼65% for 450-480 nm emission range. Simulation shows a reduction of the potential barrier due to band flattening, a more homogeneous distribution of electrons and holes in the active region and subsequently, a more radiative recombination rate with InGaN as barrier layer. Both cathodoluminescence (CL) and photoluminescence (PL) experimental results show a blue-shift of emission wavelength along with an enhancement in the emission intensity when GaN barrier is replaced with InGaN barrier, for a MQW structure both with and without the semi-bulk InGaN buffer. We attribute this blue shift to the reduced polarization mismatch and increased effective bandgap. This InGaN barrier-related improvement in IQE and efficiency droop could be useful for the realization of longer wavelength 'green-gap' range LEDs where poor IQE and efficiency droop are more prominent due to high indium (In) in the active region. [ABSTRACT FROM AUTHOR]

We report on the optimization of p-GaN layers for high indium (In) content InGaN applications by optimizing temperature, precursor CP2Mg flow rate and III/V ratio and report also on the optimization of p-contact performance. Using MOVPE, a 150 nm thick p-type GaN with moderate Mg doping and a 50 nm contact layer with high Mg doping concentration were grown on standard GaN templates at growth temperatures in the range of 850-1000 °C. Hall measurement yields hole concentration of 4.8 × 1017 cm−3 for the optimized sample. SIMS shows Mg concentration of 1.7 × 1020 cm−3 on average in the heavily doped and 4 × 1019 cm−3 on average in the moderately doped p-GaN layer for the optimized p-GaN. A multilayer Pd/Ag/Ni/Au metal contact has been deposited on this p-GaN and studied using the CTLM technique. Optimization of both p-GaN layers and p-contact processing led to a low resistance contact with specific contact resistivity of 6 × 10−4 Ω cm2. We believe, the very high Mg concentration of the surface layer in intimate contact with the contact metal reduces the Schottky barrier height and band bending. This optimization of p-GaN is an important step towards high efficiency green LEDs and solar cells. [ABSTRACT FROM AUTHOR]

We study the influence of V-pits on the overall conversion efficiency of bulk In0.12Ga0.88N based heterojunction solar cells grown by MOVPE. We show that V-pits significantly enhances the extraction of the photogenerated carriers in the InGaN absorber, resulting in a peak external quantum efficiency of 79% and a short circuit current density (twice the state of the art) of 2.56 mA/cm-2 under AM 1.5G conditions. [ABSTRACT FROM AUTHOR]

We report an AlGaN/GaN HEMT gas sensor designed to enable NO, NO2, and NH3 detection from 100 °C–400 °C over a large concentration range. Device modeling is performed to optimize several HEMT device parameters for sensing, and the experimental results show that the optimized sensor has improved performance compared with the previously reported HEMT sensors. The device shows significant no sensitivity for the first time in an HEMT device, with sensitivity up to 7% at 400 °C. In addition, high sensitivities of up to 17% are reported for NO2, and NH3 is detected at concentrations as low as 150 ppb. [ABSTRACT FROM PUBLISHER]

Recent advances in epitaxial growth have led to the growth of III-nitride devices on 2D layered h-BN. This advance has the potential for wafer-scale transfer to arbitrary substrates, which could improve the thermal management and would allow III-N devices to be used more flexibly in a broader range of applications. We report wafer scale exfoliation of a metal organic vapor phase epitaxy grown InGaN/GaN Multi Quantum Well (MQW) structure from a 5 nm thick h-BN layer that was grown on a 2-inch sapphire substrate. The weak van der Waals bonds between h-BN atomic layers break easily, allowing the MQW structure to be mechanically lifted off from the sapphire substrate using a commercial adhesive tape. This results in the surface roughness of only 1.14 nm on the separated surface. Structural characterizations performed before and after the lift-off confirm the conservation of structural properties after lift-off. Cathodoluminescence at 454 nm was present before lift-off and 458 nm was present after. Electroluminescence near 450 nm from the lifted-off structure has also been observed. These results show that the high crystalline quality ultrathin h-BN serves as an effective sacrificial layer—it maintains performance, while also reducing the GaN buffer thickness and temperature ramps as compared to a conventional two-step growth method. These results support the use of h-BN as a low-tack sacrificial underlying layer for GaN-based device structures and demonstrate the feasibility of large area lift-off and transfer to any template, which is important for industrial scale production. [ABSTRACT FROM AUTHOR]

We report the growth of high-quality triangular GaN nanomesas, 30-nm thick, on the C-face of 4HSiC using nanoselective area growth (NSAG) with patterned epitaxial graphene grown on SiC as an embedded mask. NSAG alleviates the problems of defects in heteroepitaxy, and the high mobility graphene film could readily provide the back low-dissipative electrode in GaN-based optoelectronic devices. A 5-8 graphene-layer film is first grown on the C-face of 4H-SiC by confinement-controlled sublimation of silicon carbide. Graphene is then patterned and arrays of 75-nm-wide openings are etched in graphene revealing the SiC substrate. A 30-nm-thick GaN is subsequently grown by metal organic vapor phase epitaxy. GaN nanomesas grow epitaxially with perfect selectivity on SiC, in the openings patterned through graphene. The up-or-down orientation of the mesas on SiC, their triangular faceting, and cross-sectional scanning transmission electron microscopy show that they are biphasic. The core is a zinc blende monocrystal surrounded with single-crystal wurtzite. The GaN crystalline nanomesas have no threading dislocations or V-pits. This NSAG process potentially leads to integration of high-quality III-nitrides on the wafer scalable epitaxial graphene/silicon carbide platform. [ABSTRACT FROM AUTHOR]

We report improved sensitivity to NO, NO2 and NH3 gas with specially-designed AlGaN/GaN high electron mobility transistors (HEMT) that are suitable for operation in the harsh environment of diesel exhaust systems. The gate of the HEMT device is functionalized using a Pt catalyst for gas detection. We found that the performance of the sensors is enhanced at a temperature of 600 °C, and the measured sensitivity to 900 ppm-NO, 900 ppm-NO2 and 15 ppm-NH3 is 24%, 38.5% and 33%, respectively, at 600 °C. We also report dynamic response times as fast as 1 s for these three gases. Together, these results indicate that HEMT sensors could be used in a harsh environment with the ability to control an anti-pollution system in real time. [ABSTRACT FROM AUTHOR]

In this work, wurtzite BAlN layers with boron composition as high as 12% were successfully grown by MOVPE. The growth was performed at 650 °C and then annealed at 1020 °C. Low temperature growth was used in order to alleviate B-rich phase poisoning under high TEB/III ratio. The growth was performed by continuous epitaxy as well as by flow-modulate epitaxy. BAlN single layers with clearly defined X-ray diffraction peaks were achieved on AlN templates which are appropriate substrates for deep UV devices, as well as on GaN templates to facilitate distinguishing of the XRD peak of BAlN from the substrate peak. The layer demonstrated columnar crystalline features and inherited wurtzite structure from substrates. Cross-section STEM image (bright field) of 75 nm thick BAlN layers containing 12% boron taken along the [11−2 0] zone axis. Zone A is lattice-oriented along c-axis and zone B has columnar structure; (b) higher magnification image for the top part of the layer; (c) higher magnification image for the film/substrate interface. [ABSTRACT FROM AUTHOR]

Nanoselective area growth (NSAG) of thick InGaN nanopyramid and nanostripe arrays was demonstrated using metal organic chemical vapor deposition. SiO2 nanopattern masks were fabricated using a simple and industry friendly e-beam lithography process. One hundred nanometer thick InGaN is grown with perfect selectivity over patterned GaN templates. InGaN nanostructures are homogenously pyramidal in shape, are mostly free from intrinsic material defects, and show six smooth semipolar facets. Catholuminescence emission peaks from the nanostructures are stronger than those from planar InGaN, which is due to improvement in crystal quality. The emission peaks from nanostructures are considerably redshifted from 397 to 425 nm, confirming increase in In incorporation in the nanostructures from 7 to 9% indium in InGaN. The ability to incorporate more indium depending on the geometry of the patterns and to grow selectively defect-free thick InGaN nanostructures via a simple patterning process offers a new route to develop monolithic InGaN-based high efficiency solar cells. [ABSTRACT FROM AUTHOR]

A GaN/ultrathin BGaN/GaN heterojunction is used in AlGaN/GaN high electron mobility transistors (HEMTs) to provide an electrostatic barrier to electrons and to improve the confinement of the 2-dimensional electron gas. BGaN back-barrier layers limit leakage in the GaN buffer thanks to two effects: a polarization-induced band discontinuity and a resistive barrier originating from excellent insulation properties of BGaN. Compared to conventional AlGaN/GaN HEMTs, structures grown with BGaN back-barrier showed a significant improvement of static performances, transport properties, and trapping effects involving a limited current collapse in dynamic regime. A DC maximum current increase of 58.7% was observed. [ABSTRACT FROM AUTHOR]

The spectra and optical quantum state of guided acoustic wave Brillouin scattering in optical fibers are measured. Spectra from 0.95 to 2 GHz are obtained with amplitude resolution as sensitive as 0.01 shot noise unit. Quantum homodyne tomography measurements confirm the thermal quantum statistics of guided acoustic wave Brillouin scattering, which is useful knowledge in the context of experimental continuous-variable quantum key distribution. [ABSTRACT FROM AUTHOR]

(1) Backround: Technological advances should foster gains in physicians' efficiency. For example, a reduction of the medical decision time can be enabled by faster biological tests. The main objective of this study was to collect responses from an international panel of physicians on their needs for biomarkers and also to convey the improvement in the outcome to be made possible by the potential development of fast diagnostic tests for these biomarkers. (2) Methods: we distributed a questionnaire on the Internet to physicians. (3) Results: 508 physicians participated in this survey. The mean age was 38 years. General practice and emergency medicine were heavily represented, with 95% CIs of 44% (39.78, 48.41) and 32% (27.84, 35.94)), respectively. The two most represented countries were France (95% CI: 74% (70.20, 77.83)) and the USA (95% CI: 11% (8.65, 14.18)). Ninety-eight percentages of the physicians thought that obtaining cited biomarkers more quickly would be beneficial to their practice and to patient's care. The main biomarkers of interest identified by our panel were troponin (95% CI: 51% (46.24, 54.94)), C-reactive protein (95% CI: 42% (38.03, 46.62)), D-dimer (95% CI: 29% (24.80, 32.68)), and brain natriuretic peptide (95% CI: 13% (10.25, 16.13)). (4) Conclusions: Our study highlights the real technological need for fast biomarker results, which could be provided by biosensors. The relevance of some answers such as troponin is questionable. [ABSTRACT FROM AUTHOR]

We investigate schemes for generating polarization-entangled photon pairs in standard optical fibres. The advantages of a double-loop scheme are explored through comparison with two other schemes, namely, the Sagnacloop scheme and the counter-propagating scheme. Experimental measurements with the double-loop scheme verify the predicted advantages. [ABSTRACT FROM AUTHOR]

We have developed high speed gated-mode single-photon counters based on InGaAs/InP avalanche photodiodes for use at 1.55 μm wavelength. Operation at room temperature allows afterpulse probability to be below 0.2% for gate rates up to 14 MHz. We obtained optimum noise-equivalent power of 2.2 × 10 -15 W Hz -1/2 at 14% quantum efficiency with dark-count probability of 0.2%. We propose a metric (noise-equivalent power divided by gate frequency) for comparing high speed photon counters and show that for this metric our system outperforms previously reported counters at 1.55 μm wavelength. We demonstrate that for gate widths of a nanosecond or below, the differing amplitude distributions of dark versus light counts allow an optimal decision threshold to be set for a given bias voltage. [ABSTRACT FROM AUTHOR]

Reliable p-doped hexagonal boron nitride (h-BN) could enable wide bandgap optoelectronic devices such as deep ultra-violet light emitting diodes (UV LEDs), solar blind photodiodes and neutron detectors. We report the study of Mg in h-BN layers as well as Mg h-BN/AlGaN heterostructures. Mg incorporation in h-BN was studied under different biscyclopentadienyl-magnesium (Cp2Mg) molar flow rates. 2θ-ω x-ray diffraction scans clearly evidence a single peak, corresponding to the (002) reflection plane of h-BN with a full-width half maximum increasing with Mg incorporation in h-BN. For a large range of Cp2Mg molar flow rates, the surface of Mg doped h-BN layers exhibited characteristic pleats, confirming that Mg doped h-BN remains layered. Secondary ion mass spectrometry analysis showed Mg incorporation, up to 4 × 1018 /cm3 in h-BN. Electrical conductivity of Mg h-BN increased with increased Mg-doping. Heterostructures of Mg h-BN grown on n-type Al rich AlGaN (58% Al content) were made with the intent of forming a p-n heterojunction. The I-V characteristics revealed rectifying behavior for temperatures from 123 to 423 K. Under ultraviolet illumination, photocurrent was generated, as is typical for p-n diodes. C-V measurements evidence a built-in potential of 3.89 V. These encouraging results can indicate p-type behavior, opening a pathway for a new class of wide bandgap p-type layers. [ABSTRACT FROM AUTHOR]