Individually transferrable GaN-based MQWs micro-LED structures grown on two-dimensional (2D) hexagonal boron nitride (h-BN) have been demonstrated. Different sizes (60 x 30 mu m, 60 x 60 mu m, 90 x 60 mu m and 90 x 90 mu m) of GaN-based LED heterostructures on layered h-BN were grown on dielectric SiN patterned sapphire substrates using Metal Organic Vapor Phase Epitaxy (MOVPE). Scanning electron microscope (SEM) images show micro-LEDs were grown with high selectivity within the mask opening areas. Consistent MQWs emission from micro-LEDs was observed at 452 +/- 2 nm by cathodoluminescence (CL) spectroscopy for all micro-LED sizes. The structural and optical quality were similar to the GaN-based-LEDs grown on unpatterned substrates. In addition, we have successfully demonstrated the lift-off and transfer of individual micro-LEDs to arbitrary flexible templates using a transfer printing machine, which can be addressed by full front-end process. These studies highlight the role of combination of van der Waals (vdW) epitaxy and selective area growth (SAG) in facilitating the direct realization of dimensionally defined III-Nitride micro-LED structures and the mechanical release and transfer of these micro-LEDs to templates suitable for flexible display and optogenetics applications.

Hexagonal boron nitride encapsulation is the method of choice for protecting graphene from environmental doping and impurity scattering. It was previously demonstrated that metal-organic vapor phase epitaxy (MOVPE) grows epitaxially ordered, uniform BN layers on epigraphene (graphene grown on SiC). Due to graphene's nonwetting properties, h-BN growth starts preferentially from the graphene ledges. We use this fact here to selectively promote the growth of high-quality flat h-BN on epigraphene by patterning epigraphene microstructures prior to BN growth. Thin h-BN films (down to 6 nm) grown by MOVPE show a smooth and pleated surface morphology on epigraphene, whereas crumpled BN is observed on the SiC. Cross-sectional high-resolution transmission electron microscopy images and fluorescence imaging confirm the higher BN quality grown on the epigraphene. Transport measurements reveal p-doping, as expected from hydrogen intercalation of epigraphene and regions of high and low mobility. This method can be used to produce structurally uniform high-quality h-BN/epigraphene micro/nanoscale heterostructures.

Solid state semiconductor based neutron detectors have the potential to be energy efficient and compact, making them suitable for applications where low power consumption and size constraints are important considerations. Herein, neutron detection devices based on PIN structures consisting of BGaN/GaN superlattice (SL) are demonstrated. These SL structures enable to incorporate significant boron (B) content and achieve good crystalline quality epilayers crucial for better neutron detection. Further, by leveraging the built‐in electric field generated by the PIN structure, these devices can be operated without any applied bias, simplifying overall operation and enabling a more compact size system for detection. Their performance is evaluated by measuring real‐time current response under neutron irradiation ( I N ) and without it ( I D ). The neutron induced current density (Δ J = J N − J D ) is determined, reaching an impressive value of 0.67 pA cm −2 (two times J D ) under thermal neutron flux of 1.2 × 10 4 n cm −2 s −1 without biasing, demonstrating their self‐powered capability. They exhibit a linear response to varying thermal neutron flux levels. Additionally, the detectors successfully detect low thermal neutron fluxes down to 300 n cm −2 s −1 , showcasing their potential for diverse applications, including in low neutron environments, screening nuclear warheads, and preventing illegal trafficking of radiological materials.

The AlGaN materials system has been extensively studied in order to improve the efficiency of UV‐B and UV‐C light‐emitting diodes (LEDs). While progress has been made, significant challenges remain at shorter wavelengths. Most notably, increased Al composition for shorter‐wavelength operation results in increased activation energy of Mg dopants, resulting in low p‐doping. Although p‐doped h‐BN, with a bandgap of 5.9 eV, has been proposed as a potential replacement of p‐doped AlGaN, there have not been demonstrations of LEDs fabricated from p‐doped h‐BN/AlGaN heterostructures. Such unique heterostructures combine 2D p‐doped h‐BN materials with 3D AlGaN materials. Herein, fabrication and characterization of p‐doped h‐BN/AlGaN multiple quantum wells (MQWs)/n‐AlGaN LEDs, demonstrating emission of light at 290 nm corresponding to the AlGaN MQWs, with weaker emission at 262 nm corresponding to the AlGaN barrier, are reported. These results conclusively show hole injection through p‐doped h‐BN into AlGaN and provide a proof of concept that p‐doped h‐BN can be an alternative hole injection layer for UV LEDs.

Hexagonal boron nitride (h-BN) bubbles are of significant interest to micro-scale hydrogen storage thanks to their ability to confine hydrogen gas molecules. Previous reports of h-BN bubble creation from grown h-BN films require electron beams under vacuum, making integrating with other experimental setups for hydrogen production impractical. Therefore, in this study, the formation of h-BN bubbles is demonstrated in a 20 nm h-BN film grown on a sapphire substrate with a 213 nm UV laser beam. Using atomic force microscopy, it is shown that longer illumination time induces larger h-BN bubbles up to 20 mu m with higher density. It is also demonstrated that h-BN bubbles do not collapse for more than 6 months after their creation. The internal pressure and gravimetric storage capacity of h-BN bubbles are reported. A maximum internal pressure of 41 MPa and a gravimetric storage capacity of 6% are obtained. These findings show that h-BN bubbles can be a promising system for long-term hydrogen storage. Hexagonal boron nitride (h-BN) bubbles induced using a UV laser beam are a promising system for hydrogen gas storage. These bubbles demonstrate high gravimetric storage capacity and internal pressure. In addition, h-BN bubbles exhibit long-term stability for more than 6 months after their creation. image

Hexagonal boron nitride is shown to exhibit very significant persistent photoconductivity after UV illumination. This behavior can be initiated by sub-bandgap or close to bandgap illumination. Neither temperature nor pressure affects the buildup of photoinduced carriers. The effect persists at least for months at room temperature and is maintained significantly after heating up to 300 °C. Up to six orders of magnitude increased conductivity has been durably established in the devices, and the effect is reproducible. Double exponential fitting gives time constants up to 4600 days. Irradiation after having saturated the devices is shown to drastically reduce the decay rate. The bulk origin of such effect has been demonstrated. p-hBN/n-AlGaN diodes based on magnesium doped h-BN have been used to determine the type of conductivity through studies of junction capacitance variations under UV irradiation. Depending on illumination wavelength, both n- and p-type durable photoinduced carriers can be produced. These results are of interest for UVC LEDs in which the usual conductive AlGaN layers are still a hurdle toward efficient UV emitters.

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.

Aluminium Gallium Nitride (AlyGa1-yN) quantum dots (QDs) with thin sub-µm AlxGa1-xN layers (with x > y) were grown by molecular beam epitaxy on 3 nm and 6 nm thick hexagonal boron nitride (h-BN) initially deposited on c-sapphire substrates. An AlN layer was grown on h-BN and the surface roughness was investigated by atomic force microscopy for different deposited thicknesses. It was shown that for thicker AlN layers (i.e., 200 nm), the surface roughness can be reduced and hence a better surface morphology is obtained. Next, AlyGa1-yN QDs embedded in Al0.7Ga0.3N cladding layers were grown on the AlN and investigated by atomic force microscopy. Furthermore, X-ray diffraction measurements were conducted to assess the crystalline quality of the AlGaN/AlN layers and examine the impact of h-BN on the subsequent layers. Next, the QDs emission properties were studied by photoluminescence and an emission in the deep ultra-violet, i.e., in the 275–280 nm range was obtained at room temperature. Finally, temperature-dependent photoluminescence was performed. A limited decrease in the emission intensity of the QDs with increasing temperatures was observed as a result of the three-dimensional confinement of carriers in the QDs.

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.

Passivating graphene with a layer of hexagonal boron nitride (hBN) is known to protect it from environment effects that degrade its mobility. However, growth of high-quality BN on graphene is challenging because of the lack of surface dangling bonds. Here, we report the growth of thin BN films (down to 10 nm) on monolayer epigraphene grown on silicon carbide single-crystal substrates using metal-organic vapor phase epitaxy (MOVPE). The BN film has continuous coverage on the epigraphene surface, with smooth morphology. Particles consisting of layered BN are also observed on the surface with a higher density at the step edges. High-Resolution Scanning Transmission Electron Microscopy (HRSTEM) reveals high structural quality BN layers, with a clean and abrupt interface with graphene. The BN/epigraphene/SiC heterostructure is stable up to high temperature (1550 degrees C), and annealing improves its crystallinity. These results show that MOVPE growth technique has a potential for large-scale production of BN fully coated graphene and high-temperature applications.

Giant room temperature persistent photoconductivity in hexagonal boron nitride under UVC irradiation has been demonstrated. Scanning lasers dots on sample surface at two different wavelengths (213 and 266 nm) have been used to induce such effect, the former being more efficient. Conductivity has been increased by 6 orders of magnitude upon illumination. Such increase persists significantly for at least 6 months. Decrease of photoinduced current has been shown to be 10% more important for samples irradiated under vacuum than for those irradiated under atmospheric pressure. Type of photoinduced carriers were investigated using p-hBN/n-AlGaN junctions through C/V measurements. P-type carriers are believed to be generated by 213 nm illumination whereas 266 nm laser is supposed to trigger n-type carriers.

This work deals with the effect of Sn doping at mole percentages of 1 %, 2 %, 3 % and 4 % on the structural, morphological, and optical properties of Co3O4 thin films. These physical properties were carried out by X-Ray Diffraction (XRD), Raman, Atomic Force Microscopy (AFM), scanning electron microscope (SEM), Ultraviolet-Visible-Near infrared spectroscopy (UV-Vis-NIR) and spectroscopic ellipsometry (SE). Co3O4 thin films were grown on amorphous glass substrates by spray pyrolysis technique. Experimental and modeling rigorous studies using these different techniques particularly SE were achieved in order to determinate the effect of tin doping on physical properties of cobalt oxide thin films. The incorporation of Sn into the Co sites affects drastically the optical transitions values as well as other optical properties such as the dielectric function, the band gap, the refractive index and the extinction coefficient. All doped samples exhibited a relatively higher absorption coefficient compared to the undoped ones, greater than 105 cm−1 over a wide energy range. SE analysis revealed a smaller transition of approximately 0.77 eV considered as fundamental band gap energy that was assigned to a 3d-d type within the Co2+ tetrahedral site.

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 hBN 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) 2 theta-omega 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.

Metal-semiconductor-metal (MSM) detectors based on Ti/Au and Ni/Au interdigitated structures were fabricated using 2.5 micrometer thick hexagonal boron nitride (h-BN) layer with both natural and 10B-enriched boron. Current-voltage (I-V) and current-time (I-t) curves of the fabricated detectors were recorded with (IN) and without (Id) neutron irradiation, allowing the determination of their sensitivity (S = (IN- Id)/Id= ΔI/Id). Natural and 10B-enriched h-BN detectors exhibited high neutron sensitivities of 233 and 367% at 0 V bias under a flux of 3 × 104 n/cm2/s, respectively. An imbalance in the distribution of filled traps between the two electric contacts could explain the self-biased operation of the MSM detectors. Neutron sensitivity is further enhanced with electrical biasing, reaching 316 and 1192% at 200 V and a flux of 3 × 104 n/cm2/s for natural and 10B-enriched h-BN detectors, respectively, with dark current as low as 2.5 pA at 200 V. The increased performance under bias has been attributed to a gain mechanism based on neutron-induced charge carrier trapping at the semiconductor/metal interface. The response of the MSM detectors under thermal neutron flux and bias voltages was linear. These results clearly indicate that the thin-film monocrystal BN MSM neutron detectors can be optimized to operate sensitively with the absence of external bias and generate stronger signal detection using 10B-enriched boron.

In this study, AlN epilayers were grown by ammonia-assisted molecular beam epitaxy on 3 nm h-BN grown on c-sapphire substrates. Their structural properties were investigated by comparing as-grown and postgrowth annealed layers. The role of annealing on the crystalline quality and surface morphology was studied as a function of AlN thickness and the annealing duration and temperature. Optimum annealing conditions were identified. The results of X-ray diffraction showed that optimization of the annealing recipe led to a significant reduction in the symmetric (0 0 0 2) and skew symmetric (1 0 −1 1) reflections, which was associated with a reduction in edge and mixed threading dislocation densities (TDDs). Furthermore, the impact on the crystalline structure of AlN and its surface was studied, and the results showed a transition from a surface with high roughness to a smoother surface morphology with a significant reduction in roughness. In addition, the annealing duration was increased at 1650 °C to further understand the impact on both AlN and h-BN, and the results showed a diffusion interplay between AlN and h-BN. Finally, an AlN layer was regrown on the top of an annealed template, which led to large terraces with atomic steps and low roughness.

The design of solution- processed transparent transistors with ultralow-voltage operations and a planar architecture can be a paradigm shift toward the realization of ultralow-power electronic circuits due to conformity with the existing complementary metal oxide semiconductor (CMOS) platform. We report a robust and solution-based device fabrication protocol to demonstrate near-steep-slope transparent oxide field-effect transistors (TO-FETs) with operating voltages at or below 0.5 V using a nanometer-thick amorphous indium-gallium-zinc oxide (a-IGZO) channel and an ultrathin anodized aluminum dielectric. The transmittance spectra confirm the excellent transparency (>98%) of the a-IGZO thin film for the entire visible range. Hysteresis-free transfer characteristics exhibit the film's operation as an n-channel TO-FET with a low threshold voltage (similar to 96 mV), a near-thermionic subthreshold swing (SS) down to 85 mV/dec, and a high ON/OFF current ratio (>10(5)). The consistency of these TO-FET results of ultralow-power operation with a near-steep-slope nature was demonstrated by enormously large specific capacitance values of ultrathin anodized aluminum gate dielectrics as the forcing factor. Moreover, half-volt operation of the TO-FET is also flawlessly demonstrated at room temperature with hysteresis-free characteristics. Hence, these planar TO-FETs could be a potential technological breakthrough for the future of cost-effective and high-performance transparent ultralow-power applications, including quantum and neuromorphic computation fields of research.

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 mu m-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 degrees 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.