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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.

International audience; Hexagonal boron nitride (h-BN) can be used as a p-doped material in wide-bandgap optoelectronic heterostructures or as a release layer to allow lift-off of grown three-dimensional (3D) GaN-based devices. To date, there have been no studies of factors that lead to or prevent lift-off and/or spontaneous delamination of layers. Here, we report a unique approach of controlling the adhesion of this layered material, which can result in both desired lift-off layered h-BN and mechanically inseparable robust h-BN layers. This is accomplished by controlling the diffusion of Al atoms into h-BN from AlN buffers grown on h-BN/sapphire. We present evidence of Al diffusion into h-BN for AlN buffers grown at high temperatures compared to conventional-temperature AlN buffers. Further evidence that the Al content in BN controls lift-off is provided by comparison of two alloys, Al 0.03 B 0.97 N/sapphire and Al 0.17 B 0.83 N/sapphire. Moreover, we tested that management of Al diffusion controls the mechanical adhesion of high-electron-mobility transistor (HEMT) devices grown on AlN/h-BN/sapphire. The results extend the control of two-dimensional (2D)/3D hetero-epitaxy and bring h-BN closer to industrial application in optoelectronics.

International audience; (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.

International audience; We report wafer-scale growth and mechanical exfoliation of 20 periodAl0.58Ga0.42N/Al0.37Ga0.63N multiple quantum wells (MQWs) on h-BN buffered templates and compare them to control samples of the same structure on AlN templates. X-ray diffraction measurements of the MQW structure on h-BN clearly featured satellite peaks up to third order in the 2θ−ω scans indicating good MQW periodicity. Detailed transmission electron microscope (TEM) analysis show good heterointerface quality in the structure and large V-pits on the surface. Depth resolved cathodoluminescence of the MQWs on h-BN revealed a UV emission peak at 299 nm and a sharp shoulder at 292 nm. We also report lift-off and transfer of the MQW on the h-BN structure and have investigated post-transfer optical emission, which demonstrates good preservation of optical emission characteristics. Together these results show the suitability of h-BN buffers for the realization of free-standing or flexible optical devices emitting in the deep UV region.

International audience; We demonstrate the fabrication of vertical InGaN light-emitting diodes (LEDs) on large-area free-standing membranes, using a mechanical lift-off technique enabled by 2D h-BN. 30 μm-thick electroplated copper deposited on the epilayer (i) gives rigidity to the structure, preventing crack generation, (ii) functions as a back mirror and as a heat sink, and (iii) enables one-step self-lift-off and transfer of LED structures from h-BN/sapphire during a thermal treatment at 100 °C. Free-standing arrays of LEDs on thick membranes were processed and their electro-optical performance was characterized. This approach can provide a solution for the fabrication of low-cost, wafer scale, crack-free, and highly reproducible free-standing arrays of vertical LEDs with up to centimeter-size areas.

International audience; We present a critical study of LEDs on h-BN compared to the conventional LEDs on sapphire from materials characterizations, device fabrication to the device performances measurements performed before and after liftoff and transfer with and without intermediary adhesion layer to arbitrary substrates.

International audience; Combined photonic and electronic systems require diverse devices to be co-integrated on a common platform. This heterogeneous integration is made possible through several separation and transfer methods where the functioning epilayers are essentially released from their growth substrate. The use of 2D layered h-BN as a mechanical release layer has been demonstrated to be a promising technique for the hybrid integration of III-nitride devices. In this talk we will give an overview of our results on wafer-scale van der Waals epitaxy by MOVPE of different III-N heterostructure devices such as LEDs, HEMTs, solar cells, sensors and photodetectors. Furthermore, mechanical release and transfer techniques of crack-free III-N devices on foreign substrates will be presented along with a comparison between the device performances before and after transfer.

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. 2&theta, &omega, 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 &times, 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.

Selective Area van der Waals Epitaxy (SAVWE) of III-Nitride device has been proposed recently by our group as an enabling solution for h-BN-based device transfer. By using a patterned dielectric mask with openings slightly larger than device sizes, pick-and-place of discrete LEDs onto flexible substrates was achieved. A more detailed study is needed to understand the effect of this selective area growth on material quality, device performance and device transfer. Here we present a study performed on two types of LEDs (those grown on h-BN on patterned and unpatterned sapphire) from the epitaxial growth to device performance and thermal dissipation measurements before and after transfer. Millimeter-size LEDs were transferred to aluminum tape and to silicon substrates by van der Waals liquid capillary bonding. It is shown that patterned samples lead to a better material quality as well as improved electrical and optical device performances. In addition, patterned structures allowed for a much better transfer yield to silicon substrates than unpatterned structures. We demonstrate that SAVWE, combined with either transfer processes to soft or rigid substrates, offers an efficient, robust and low-cost heterogenous integration capability of large-size devices to silicon for photonic and electronic applications.

We report an elongation of emission wavelength by inserting a ∼70 nm thick high quality semi-bulk (SB) InyGa1-yN buffer layer underneath the InxGa1-xN/InyGa1-yN (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).

International audience; Boron rich BAlN alloys have been grown on 2-inch sapphire substrates by Metal-Organic Vapor Phase Epitaxy. The surface morphology of BAlN alloys exhibits a transition stage from a completely two-dimensional to a three-dimensional granular surface with an increased trimethylaluminum/group III (TMAl/III) ratio. Only a shift in the position of the 002 plane reflection peak to higher diffraction angles in the 2θ−ω scan along with a decrease in intensity was observed, specifying formation of layered BAlN alloys up to a TMAl/III ratio of 14. AlN phase separation was observed while increasing the TMAl/III ratio to 25, supporting SEM observations. Secondary-ion mass spectrometry measurements confirmed the presence of up to 17% Al in layered BAlN alloy systems. A cross sectional transmission electron microscopy (TEM) study confirmed the layered nature of single phase BAlN alloys. It also revealed the presence of wurtzite Al rich BAlN phases in a matrix of layered hexagonal B rich BAlN. Band to band transition around 5.86 eV has been observed, which shifted slightly to lower energy with increasing Al incorporation. The bowing parameter (C) in boron rich BAlN alloy systems was evaluated to be around 0.65 ± 0.05 eV. Encouraging results were obtained on boron rich BAlN alloy formation, motivating further exploration of growth conditions and study of BAlN fundamental properties for applications in deep UV optoelectronics.Hexagonal boron nitride (h-BN) is a unique III-nitride, which has interesting properties such as a layered structure, high thermal conductivity, and a wide bandgap (∼6 eV).1–5 Even though h-BN is an indirect bandgap semiconductor, it has an impressive deep ultraviolet (UV) emission and, hence, it is very promising for applications in deep UV optoelectronics when compared to direct bandgap AlN and other materials.3,6–13 The AlN alloy system, on the other hand, is the most studied material for applications in the deep UV regime, but growth of high quality materials and p-type doping are challenging.6,14 Both Al rich w-BAlN and B rich h-BAlN alloys may enable a desirable bandgap and lattice/strain engineering for applications. For example, h-BN can be made into a direct bandgap material through strain engineering or alloying with Al, which would enhance emission efficiency in the deep UV for UV LEDs. Alloying boron into AlN could also lead to a type II BAlN/AlGaN heterojunction,15 allowing the achievement of an electron blocking layer. BAlN has also been studied as a promising material candidate for high-reflectivity distributed Bragg reflectors (DBRs) due to strong refractive index modification.16,17 Because of their layered nature and reported intrinsic p-type behavior, the use of h-BN based alloys may give more flexibility to design highly efficient device structures.18–20 Theoretically, it was reported that BAlN alloys can have structural crossover from hexagonal to wurtzite at 50% of boron, and the band-gap transition from indirect to direct would occur at 75% of boron.21,22Apart from these theoretical investigations, boron rich BAlN alloys have not yet been explored experimentally. The growth of boron rich BAlN alloys and the understanding of its basic structural, as well as the optical, properties are of high importance. In this work, we report growth of single-phase boron rich BAlN alloys up to 17% of Al in a Metal-Organic Vapor Phase Epitaxy (MOVPE) reactor. We first studied in detail the relationship between morphology, Al composition, and the trimethylaluminum/group III (TMAl/III) ratio. Second, the bandgap variation in boron rich BAlN and the bowing effect were presented.The BAlN alloys were grown directly on c-plane sapphire substrates without any buffer in an Aixtron MOVPE close coupled showerhead (CCS) reactor. Triethylboron (TEB), trimethylaluminum (TMAl), and ammonia (NH3) were precursors for boron, aluminum, and nitrogen, respectively. 20 nm thick of BAlN layers were grown at 1280 °C and 90 mbar pressure. The TMAl/III ratio was varied from 0 to 25; in order to increase the Al content in gas phase, all other parameters were kept constant.A scanning electron microscope (SEM) was used to study the surface morphology of the samples. The crystalline structure and phase purity of BAlN alloys were examined by high-resolution X-ray diffraction (HRXRD) scans, performed in a Panalytical X'pert Pro Materials Research Diffractometers system with Cu Kα radiation in triple axis mode. The aluminum content was estimated by Secondary-ion mass spectrometry (SIMS) using Cs+ molecular ions. The interfaces of heterostructures were characterized by high-angle Annular Dark Field Scanning Transmission electron Microscopy (HAADF-STEM) performed on an aberration-corrected JEOL 2200FS electron transmission microscope. Prior to this study, cross sectional lamellae were prepared by the FIB process after coating a 100 nm thick carbon for layer protection. Transmission spectra were measured at room temperature with a Perkin Elmer LAMBDA 950 spectrophotometer.

International audience; In article number 1900164 by Abdallah Ougazzaden and co‐workers, III‐Nitride based LEDs have been locally grown on h‐BN and fabricated at a wafer‐scale. This enables a simple and a dicing‐free pick‐and‐place of the devices on a flexible substrate without performance degradation.

International audience; Gas sensors based on AlGaN/GaN transistors are fabricated using platinum gate to detect and to quantify H2 (1.5-10%) and O2 (1.5-100%) species at high temperature (500 °C). The metrics ΔI/Δt measured within the 5 first seconds of the transient response to the target gas exposure is used to quantify the performance of the sensors. A linear relation between ΔI/Δt and gas concentration is found. ΔI/Δt increases with gas concentration and decreases at high temperature. Sensor sensitivity increases when gas concentration increases. For H2 gas, it is noticed that the sensitivity increases when temperature increases. Sensors response and recovery times decrease as gas concentration increases and decrease when temperature decreases.

International audience; InGaN nano-structures, grown using nano selective area growth, have been shown to exhibit high crystalline quality, even for high In content InGaN alloy, and reduced polarization charge effect. They are thus very attractive for the realization of high efficiency solar cells. Compared to planar InGaN absorbers, nanopyramid-based absorbers are shown to relax the usual challenging constraint on the doping of the p-GaN layer, which would be needed to overcome the polarization-induced electric field. NP-based solar cells maintain the same performance with ten times lower p-GaN doping. Furthermore, the SiO2 mask used for selective area growth of the nanopyramids is shown to help trap light into the nanopyramids, leading to increased optical absorption and thus efficiency. Last, InGaN nanopyramid absorber-based solar cells can allow for a higher InGaN residual donor concentration than that of the planar InGaN solar cells. Overall, an optimized In0.3Ga0.7N nanopyramid-based solar cell can lead to an efficiency twice than that of a planar InGaN-based solar cells with standard p- and n-GaN doping level. As a proof of concept, an In0.09Ga0.91N nanopyramid-based solar cell has been fabricated and is shown to have larger short circuit photocurrent and open circuit voltage than a state of the art In0.08Ga0.92N-based planar solar cell.

International audience; In article number 1900207, Suresh Sundaram, Abdallah Ougazzaden, and co‐workers demonstrate self‐organized GaN nanorods formation on layered h‐BN templates by van der Waals epitaxial growth. This approach is used to grow III‐N nanowire light‐emitting diodes. In addition, this approach also mitigates transfer processes and scaling issues seen with other 2D materials, since both the 1D (GaN nanorods) and 2D (h‐BN) are grown at the wafer‐scale and in one epitaxial growth run.

International audience; Hexagonal boron nitride (h‐BN) is a promising 2D template that decouples substrate effects from the layer above it by van der Waals epitaxy, because there are only weak forces out of the h‐BN. It also permits convenient mechanical transfer of devices grown on their surface to an appropriate substrate. Here, van der Waals epitaxial growth resulting in the formation of self‐organized GaN nanorods on h‐BN templates is demonstrated. This approach to the growth of III‐N nanostructures avoids transfer processes and scaling issues seen with other 2D materials, since both the 1D (GaN nanorods) and 2D (h‐BN) are grown at the wafer‐scale and in one growth run. Further, this process is used to grow vertical core–shell p‐GaN/InGaN/n‐GaN nano‐PIN device structures on wafer‐scale 2D h‐BN on sapphire and silicon substrates. The high quality of the core–shell nanostructures is confirmed by detailed electron microscopy study, which gives more insight into the nanorod formation mechanism on 2D material. Mechanical transfer of nanostructures on sapphire substrates to copper tape is then demonstrated, with no resulting damage of nanorods. Use of MOVPE grown large‐area h‐BN to realize nanostructures is a significant advancement and can lead to new nanodevice architectures needed for next‐generation optoelectronic devices.

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

p-GaN/i-InGaN/n-GaN (PIN) structures were grown epitaxially on ZnO-buffered c-sapphire substrates by metal organic vapor phase epitaxy using the industry standard ammonia precursor for nitrogen. Scanning electron microscopy revealed continuous layers with a smooth interface between GaN and ZnO and no evidence of ZnO back-etching. Energy Dispersive X-ray Spectroscopy revealed a peak indium content of just under 5 at% in the active layers. The PIN structure was lifted off the sapphire by selectively etching away the ZnO buffer in an acid and then direct bonded onto a glass substrate. Detailed high resolution transmission electron microscoy and grazing incidence X-ray diffraction studies revealed that the structural quality of the PIN structures was preserved during the transfer process.

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.

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.

International audience; GaN is a durable, radiation hard and wide-bandgap semiconductor material, making it ideal for usage with betavoltaic batteries. This paper describes the design, fabrication and experimental testing of 1 cm$^2$ GaN-based betavoltaic batteries (that achieve an output power of 2.23 nW) along with a full model that accurately simulates the device performance which is the highest to date (to the best of our knowledge) for GaN-based devices with a $^{Ni}$63 source.

Due to its high absorption coefficient and variable bandgap, InGaN is being intensively studied for photovoltaic applications. Growth of thick homogenous InGaN absorbers is challenging due to relaxation, clustering, and transition from 2D to 3D growth. These issues can be avoided by a semibulk multilayer structure. In this work, we analyze InGaN-based semibulk-structured solar cells in detail. We show that for indium content lower than 15%, GaN interlayers’ thickness has no influence on carrier transport due to the low barrier height. A conversion efficiency of 2.4% can be expected for this indium content. However, for higher indium content (15–30%), we show that the thinner the GaN interlayers, the better the conversion efficiency. Beyond 30% of indium, the conversion efficiency is hindered by the barriers’ important height even for very thin thicknesses of GaN interlayers. We show also that, for semibulk structure, both growth direction (N-face and metal-face) have similar impact on efficiency. This theoretical study gives the guidelines for the fabrication of InGaN-based solar cells that can be used as a wide-bandgap top cell in multijunction solar cells.

In0.16Ga0.84N/In0.05Ga0.95N Multiple Quantum Well (MQW) structure grown on a 70 nm thick high quality semi-bulk InGaN buffer layer is reported. Temperature dependent photoluminescence (PL) reveals 67.5% of room temperature Internal Quantum Efficiency (IQE) at an emission peak of ∼455 nm with FWHM of 20 nm. Low temperature PL study shows clear improvement in emission intensity when conventional GaN buffer and GaN barrier are replaced by semi-bulk InGaN buffer in addition with InGaN barrier. Simulation confirms improved IQE and reduced efficiency droop when using semi-bulk as buffer which is attributed to the improved overlapping of electron-hole wave functions due to the reduced internal electric field from counteraction by surface polarization field. This efficiency improvement is very beneficial for high In content green LEDs where the efficiency is limited by polarization induced Quantum Confined Stark Effect (QCSE) for excess indium content.

International audience; Nanoselective area growth (NSAG) by metal organic vapor phase epitaxy of high-quality InGaN nanopyramids on GaN-coated ZnO/c-sapphire is reported. Nanopyramids grown on epitaxial low-temperature GaN-on-ZnO are uniform and appear to be single crystalline, as well as free of dislocations and V-pits. They are also indium-rich (with homogeneous 22% indium incorporation) and relatively thick (100 nm). These properties make them comparable to nanostructures grown on GaN and AlN/Si templates, in terms of crystallinity, quality, morphology, chemical composition and thickness. Moreover, the ability to selectively etch away the ZnO allows for the potential lift-off and transfer of the InGaN/GaN nanopyramids onto alternative substrates, e.g. cheaper and/or flexible. This technology offers an attractive alternative to NSAG on AlN/Si as a platform for the fabrication of high quality, thick and indium-rich InGaN monocrystals suitable for cheap, flexible and tunable light-emitting diodes.

International audience; The mechanical release of III‐nitride devices using h‐BN is a promising approach for heterogeneous integration. Upscaling this technology for industrial level requires solutions that allow a simple pick‐and‐place technique of selected devices for integration while preserving device performance. An advance that satisfies both of these requirements is demonstrated in this work. It is based on a lateral control of the h‐BN quality, using patterned sapphire with a SiO2 mask, to achieve localized van der Waals epitaxy of high‐quality GaN based device structures. After process fabrication, the devices can be individually picked and placed on a foreign substrate without the need for a dicing step. In addition, this approach could reduce delamination of h‐BN on large diameter substrates because each h‐BN region is smaller, with independent device structures. Discrete InGaN LEDs on h‐BN are grown and fabricated on 2 in. patterned sapphire using a SiO2 mask. A set of devices are selectively released and transferred to flexible aluminum tape. The transferred LEDs exhibit blue light emission around 435 nm. The approach presented here is scalable on any wafer size, can be applied to other types of nitride‐based devices, and can be compatible with commercial pick‐and‐place handlers for mass production.

AlGaN/GaN distributed Bragg reflectors have been grown on GaN templates by Metal Organic Vapor Phase Epitaxy (MOVPE). To overcome the problem of crack generation and achieve high reflectivity with an optimum number of periods a simple approach has been investigated. Using this approach, a coherently strained 20-pair Al 0.27 Ga 0.73 N/GaN (42 nm/36 nm) DBR has been designed and grown. No cracks were observed over 2” wafer. Around 90% reflectivity at 384 nm and a stop-bandwidth of 18 nm was obtained by having good crystalline quality and abrupt and flat interfaces.

We report the numerical study of n-GaN/i-InGaN/p-GaN solar cells on Ga-face substrates with thin GaN interlayers present in the intrinsic InGaN region. These interlayers have recently been shown to significantly increase the crystal quality of thick InGaN layers $$(>\!\!\!120\,\text{ nm})$$ . We find that tunneling is efficient in n-i-p structures having interlayers $$\le \! 1.5\,\text{ nm}$$ thick if polarization charges are sufficiently screened. If left unscreened, the large polarization charges naturally formed at the heterointerfaces degrades n-i-p performance, at a given interlayer thickness, because polarization charges increase the distance that carriers must tunnel. Simulations identify favorable parameter ranges.

International audience; We report an AlGaN/GaN HEMT gas sensor designed to enable NO, NO 2 , and NH 3 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 NO 2 , and NH 3 is detected at concentrations as low as 150 ppb.

International audience; This article reports on two-dimensional (2D) layered hexagonal BN (h-BN) grown on sapphire by metalorganic vapor phase epitaxy (MOVPE). The highly oriented lattice and hexagonal phase of the epitaxial layers were confirmed by X-ray diffraction, Raman spectrum, and cross-section scanning transmission electron microscopy. The surface of BN over a 2-in. wafer exhibits specific 2D material morphology features for different BN thicknesses, from an atomically flat surface to a honeycomb wrinkle network. The grown epitaxial layers demonstrate a large absorption coefficient (∼106 cm–1) above the bandgap energy of 5.87 eV with direct band transition behavior. Near-bandgap luminescence at 216.5 nm (5.73 eV) and characteristic defect band recombination at longer wavelengths were observed by cathodoluminescence at 77 K. This wafer-scale MOVPE-grown layered h-BN with different 2D morphology and with near bandgap emission can facilitate applications such as graphene-based electronics, advanced van der Waals heterostructures, and deep UV photonics.

International audience; We report nano-selective area growth (NSAG) of BGaN by MOCVD on AlN/Si(111) and GaN templates resulting in 150 nm single crystalline nanopyramids. This is in contrast to unmasked or micro-selective area growth, which results in a multi-crystalline structure on both substrates. Various characterization techniques were used to evaluate NSAG as a viable technique to improve BGaN material quality on AlN/Si(111) using results of GaN NSAG and unmasked BGaN growth for comparison. Evaluation of BGaN nanopyramid quality, shape and size uniformity revealed that the growth mechanism is the same on both the templates. Further STEM analysis of BGaN nanopyramids on AlN/Si (111) templates confirmed that these are single-crystalline structures without any dislocations, likely due to single nucleation occurring in the 80 nm mask opening. CL results correspond to boron content between 1.7% and 2.0% in the nanopyramids. We conclude that NSAG is promising for growth of high-quality BGaN nanostructures and complex nano-heterostructures, especially for low-cost silicon substrates.

In this paper we report on a spontaneous 2D/3D transition observed in InGaN alloys after 60 nm of growth. This transition is responsible for the formation of a stack of distinct InGaN layers. The driving mechanism is shown to be lateral fluctuations of the indium composition, that arise to accommodate the increasing strain energy of the InGaN layer. Three distinct stages of growth have been identified. First, a homogeneous, 2D InGaN layer forms, pseudomorphically strained on the underlying GaN. Then, at around 30 nm large lateral fluctuations of the indium composition are observed and a second pseudomorphic layer, composed of indium-rich and indium-poor clusters, is formed. Finally induces a 2D/3D transition at 60 nm and a 3D InGaN layer is formed.

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.

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-NO 2 and 15 ppm-NH 3 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.

Recent plasmonics experiments focus light to 10 nm focal spots. We show that with such illumination, electrostatically gated graphene nanoribbon photoconductors produce photocurrents whose direction depends on illumination wavelength.

At the present time, serious threats are being posed to the environment due to pollutants in both the air (e.g. automotive exhaust emissions) and water (e.g. phosphates, nitrates, heavy metals). In an effort to improve these environmental hazards, automotive emissions standards and regulations on water pollutants are becoming more and more strict each year. One of the major limitations in meeting these regulations is the ability to quickly and accurately detect low concentrations of the target molecules.We report the fabrication and experimental testing of a new generation of microsensor technology that can detect a wide range of gases in the air as well as pollutants in a liquid environment. These sensors are based on AlGaN/GaN high electron mobility transistors (HEMT) with functionalized gate contacts acting as the sensing layer. The use of high bandgap, group-III nitride semiconductor materials gives the sensors a high thermal and chemical stability, making them suitable for high temperature applications (above 600°C) and in harsh chemical conditions. Depending on the type and structure of functional layer, the adsorption of the target molecules leads to change the surface depletion layer which has a direct affect on the sensitivity and the selectivity of the device. Extensive modeling and design of the AlGaN/GaN HEMTs has been performed to optimize the devices for detection of exhaust gases and water pollutants. This includes the design of each of the material parameters (e.g. AlGaN thickness, Al incorporation) and the functionalized contacts (e.g. material, dimensions, morphology).Experimental results using a Pt sensing layer show detection of 10–1000 ppm NO and NO2 gas with changes in current of 0.8 and 2.8 mA, respectively. Detection of NH3 gas in a range of 150 ppb–15 ppm was also demonstrated, and can be compared to detection limits of only 35 ppm for similar devices. This is the first time that detection of NO has been demonstrated using a HEMT sensor, and the first time selective detection of NO, NO2, and NH3 has been demonstrated using a single transistor device. Furthermore, the sensitivity to NO2 and NH3 were significantly higher in our optimized device compared to other HEMT sensors. Dynamic response times were shown to be between 1–3 seconds for each gas, showing that these sensors can perform in real-time applications.In addition to exhaust gas detection, an open-gate HEMT sensor was designed and fabricated as a water pollution sensor and showed detection of both phosphates and nitrates in water. This is the first time that phosphates have been detected using a HEMT sensor, and shows that HEMT sensors can be useful in the prevention of eutrophication of fresh water bodies. We are currently exploring HEMT sensor designs for the detection other water pollutants such as heavy metals, inorganic and organic molecules that damage or contaminate water supplies.The experimental results presented in this abstract demonstrate that the functionalized AlGaN/GaN HEMT sensors we have developed are promising for real-time air and water treatment applications due to their low detection limits, high sensitivities, fast response times, and selectivity by functionalizing the sensing layer for specific target molecules. Therefore, this technology has the potential to drastically improve the reduction of pollution in the air caused by automotive exhaust and other gases, as well as pollution in lakes and other viable sources of water.

International audience; 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.

International audience; We report a double Schottky junction gas sensor based on a BGaN/GaN superlattice and Pt contacts. NO2 is detected at concentrations from 4.5 to 450 ppm with current responsivity of 6.7 mA/(cm(2) x ppm) at 250 degrees C with a response time of 5 s. The sensor is also selective against NH3 at least for concentrations less than 15 ppm. The BGaN layer at the surface increases surface trap density and trap depth, which improves responsivity and high temperature stability while the GaN layer improves the magnitude of the diode current. The BGaN layer's columnar growth structure also causes a Pt morphology that improves O2- diffusion.

International audience; We propose to use two new approaches that may overcome the issues of phase separation and high dislocation density in InGaN-based PIN solar cells. The first approach consists in the growth of a thick multi-layered InGaN/GaN absorber. The periodical insertion of the thin GaN interlayers should absorb the In excess and relieve compressive strain. The InGaN layers need to be thin enough to remain fully strained and without phase separation. The second approach consists in the growth of InGaN nano-structures for the achievement of high In content thick InGaN layers. It allows the elimination of the preexisting dislocations in the underlying template. It also allows strain relaxation of InGaN layers without any dislocations, leading to higher In incorporation and reduced piezo-electric effect. The two approaches lead to structural, morphological, and luminescence properties that are significantly improved when compared to those of thick InGaN layers. Corresponding full PIN structures have been realized by growing a p-type GaN layer on the top the half PIN structures. External quantum efficiency, electro-luminescence, and photo-current characterizations have been carried out on the different structures and reveal an enhancement of the performances of the InGaN PIN PV cells when the thick InGaN layer is replaced by either InGaN/GaN multi-layered or InGaN nanorod layer.

(In)GaN p-i-n structures were grown by MOVPE on both GaN- and ZnO-coated c-sapphire substrates. XRD studies of the as-grown layers revealed that a strongly c-axis oriented wurtzite crystal structure was obtained on both templates and that there was a slight compressive strain in the ZnO underlayer which increased after GaN overgrowth. The InGaN peak position gave an estimate of 13.6at% for the indium content in the active layer. SEM and AFM revealed that the top surface morphologies were similar for both substrates, with an RMS roughness (5 μm x 5 μm) of about 10 nm. Granularity appeared slightly coarser (40nm for the device grown on ZnO vs 30nm for the device grown on the GaN template) however. CL revealed a weaker GaN near band edge UV emission peak and a stronger broad defect-related visible emission band for the structure grown on the GaN template. Only a strong ZnO NBE UV emission was observed for the sample grown on the ZnO template. Quarter-wafer chemical lift-off (CLO) of the InGaN-based p-i-n structures from the sapphire substrate was achieved by temporary-bonding the GaN surface to rigid glass support with wax and then selectively dissolving the ZnO in 0.1M HCl. XRD studies revealed that the epitaxial nature and strong preferential c-axis orientation of the layers had been maintained after lift-off. This demonstration of CLO scale-up, without compromising the crystallographic integrity of the (In)GaN p-i-n structure opens up the perspective of transferring GaN based devices off of sapphire substrates industrially.