Infra red and Ultraviolet radiation Research Papers (original) (raw)

2025

Electronic structure and vibrational characteristics of GaAlN wurtzoids at the molecular-nanoscale limit are investigated. The investigated properties include energy gap, vibrational properties, and phase stability against transition to GaAlN diamondoids. At the molecular-nanoscale limit, wurtzite GaAlN nanocrystals are represented by wurtzoids. The properties of GaAlN molecules and nanocrystals as a function of Ga and Al contents are shown. The results show that the energy gap depends on size, shape and surface conditions. Molecules with hydrogen passivated surface have wide energy gap while bare molecules have smaller energy gaps. On the other hand, vibrational longitudinal optical mode of bare molecules experiences a redshift after surface hydrogen passivation with smaller vibrational reduced masses and force constant at a given frequency. Differences between GaAlN two limits (GaN and AlN) are explained by the existence of d orbitals in Ga atoms. Calculated Gibbs free energy of atomization show the stability of wurtzoids against transition to the diamondoids at the molecular-nanoscale limit for both bare and hydrogen passivated cases.

2025, Astrophysics and Space Science

2024, British Journal of Dermatology

Background Several hundred million of the 3 billion formally employed people worldwide are at risk from high levels of solar ultraviolet radiation (UVR). Chronic light damage to the skin can lead to nonmelanoma skin cancer (NMSC), especially when irradiation is too high and is acquired for decades. However, data with uniform metrics, high resolution over time and in-depth occupational profiles are not available. Objectives To build a worldwide usable matrix of UVR exposure in occupations and to show use cases for the data. Methods One thousand test persons were recruited to wear electronic data logger dosimeters during their working time for 7 months each. The measurements yielded 3.7 billion data points for around 48 000 days with high-quality data capture covering more than 250 occupations and 650 activities. Scientific evaluation of the data included daily and half-hourly means, geographical transfer calculations to the world, threshold exceedance quotas, transcriptome effects, a...

2024, Bioprocess and Biosystems Engineering

Due to recent global warming threats, the changes in the atmosphere have caused significant ultraviolet (UV) radiation exposure, primarily emitted by the sun, which creates more awareness of photoprotection. Sunscreen development has been a convenient and crucial approach to photoprotection against ultraviolet radiation. Due to high demand, upgrading the quality of sunscreen products and certifying methods are necessary to guarantee the safety of commercial sunscreen products for use. Sunscreen products should have a satisfactory amount of sun protection factor (SPF), ultraviolet A protection factor, as well as the photostability of the sunscreens for them to be considered effective and safe for use. A rigorous study on the effectiveness of the sunscreen components and their safety standards is essential for the productive use and further improvement of the available sunscreen materials. This article summarizes the effects and issues, protective measures of sunscreen usage, and its components, mainly ultraviolet filters.

2024

Smart, low cost and environmentally safe aluminum gallium nitride (AlGaN)-based ultraviolet-B light-emitting diodes (UV-B LEDs) are promising in real-world applications including medical as well as agricultural sciences. Higher efficiency droops, low hole injection efficiency, and high operating voltage are the key problems that AlGaN-based UV-B LEDs are facing. In this work, a smart and clean AlGaN-based UV-B LED at 284 nm emission wavelength has been studied. Here an approach is presented to electrically operate the quantum tunnelling probability by exploiting the transported carriers at the interface of p-AlGaN/n-AlGaN/n ++-AlGaN tunnel junction (TJ) with moderate Si and Mg-doping levels and optimized thickness with the help of simulation study. The simulation results show that the Augur recombination rate is successfully suppressed and quite a high radiative recombination rate is achieved in the 284 nm N-polar AlGaN-based TJ UV-B LEDs, which is attributed to the improved hole injection toward the MQWs when compared to C-LED (conventional-LED). It is found that C-LED has a maximum IQE (internal quantum efficiency) of 40% under 200 A cm −2 injection current with an efficiency drop of 15%, while the TJ-LED has a maximum IQE of 93% with an efficiency droop of 0%. In addition, TJ-based AlGaN LED emitted power has been improved by 6 times compared to the C-LED structure. The emitted powers of TJ-LED increase linearly under varying current densities, whereas in the case of C-LED, the emitted power changes nonlinearly under varying current densities. This is attributed to the lower Augur recombination rate in the MQWs of N-AlGaN-based TJ UV-B LED. The operating voltages were reduced from 5.2 V to 4.1 V under 200 mA operation, which is attributed to the thickness and doping optimization in TJ and better selection of relatively lower Al-content in the contact layer. N-polar AlGaN-based TJ is explored for UV-B LEDs and the demonstrated work opens the door to epitaxial growth of high-performance UV emitters in MOCVD and MBE for a plethora of biomedical applications.

2024, Epj Web of Conferences

Light emitting diode (LED) employed a numerous applications such as displaying information, communication, sensing, illumination and lighting. In this paper, InGaN/AlGaN based on one quantum well (1QW) light emitting diode (LED) is modeled and studied numerically by using COMSOL Multiphysics 5.1 version. We have selected In0.06Ga0.94N as the active layer with thickness 50nm sandwiched between 0.15µm thick layers of p and n-type Al0.15Ga0.85N of cladding layers. We investigated an effect of doping concentration on InGaN/AlGaN double heterostructure of light-emitting diode (LED). Thus, energy levels, carrier concentration, electron concentration and forward voltage (IV) are extracted from the simulation results. As the doping concentration is increasing, the performance of threshold voltage, Vth on one quantum well (1QW) is also increases from 2.8V to 3.1V.

2024, Applied Physics Letters

Metals have been studied as terahertz sources for decades. Recent research has shown the potential of metals in generating extremely high THz pulse energy excited by intense laser pulses. To avoid the metal surface debris caused by laser pulses, here, we report the results of the broadband terahertz wave emission from a flowing liquid metal line excited by subpicosecond laser pulses. The THz signal emitted from the liquid gallium line shows the stronger field with the broader bandwidth compared to the signal from water under the identical optical excitation conditions. Our preliminary study suggests that the liquid metals have the potential to serve as efficient and powerful THz sources for the intense lasers with a high repetition rate.

2024, arXiv (Cornell University)

Using Fisher information matrices, we forecast the uncertainties σ M on the measurement of a "Planet X" at heliocentric distance d X via its tidal gravitational field's action on the known planets. Using planetary measurements currently in hand, including ranging from the Juno, Cassini, and Mars-orbiting spacecraft, we forecast a median uncertainty (over all sky positions) of σ M = 0.22M ⊕ (d x /400 AU) 3. A 5σ detection of a 5M ⊕ Planet X at d X = 400 AU should be possible over the full sky but over only 5% of the sky at d X = 800 AU. The gravity of an undiscovered Earth-or Mars-mass object should be detectable over 90% of the sky to a distance of 260 or 120 AU, respectively. Upcoming Mars ranging improves these limits only slightly. We also investigate the power of high-precision astrometry of ≈ 8000 Jovian Trojans over the 2023-2035 period from the upcoming Legacy Survey of Space and Time (LSST). We find that the dominant systematic errors in optical Trojan astrometry (photocenter motion, non-gravitational forces, and differential chromatic refraction) can be solved internally with minimal loss of information. The Trojan data allow cross-checks with Juno/Cassini/Mars ranging, but do not significantly improve the best-achievable σ M values until they are 10× more accurate than expected from LSST. The ultimate limiting factor in searches for a Planet X tidal field is confusion with the tidal field created by the fluctuating quadrupole moment of the Kuiper Belt as its members orbit. This background will not, however, become the dominant source of uncertainty until the data get substantially better than they are today.

2024, Nature Communications

Harnessing photoexcited “hot” carriers in metallic nanostructures could define a new phase of non-equilibrium optoelectronics for photodetection and photocatalysis. Surface plasmons are considered pivotal for enabling efficient operation of hot carrier devices. Clarifying the fundamental role of plasmon excitation is therefore critical for exploiting their full potential. Here, we measure the internal quantum efficiency in photoexcited gold (Au)–gallium nitride (GaN) Schottky diodes to elucidate and quantify the distinct roles of surface plasmon excitation, hot carrier transport, and carrier injection in device performance. We show that plasmon excitation does not influence the electronic processes occurring within the hot carrier device. Instead, the metal band structure and carrier transport processes dictate the observed hot carrier photocurrent distribution. The excellent agreement with parameter-free calculations indicates that photoexcited electrons generated in ultra-thin Au ...

2024, ACS Applied Materials & Interfaces

One-dimensional (1D) structures-based UV-light-emitting diode (LED) has immense potential for next-generation applications. However, several issues related to such devices must be resolved first, such as expensive material and growth methods, complicated fabrication process, efficiency droop, and unavoidable metal contamination due to metal catalyst that reduces device efficiency. To overcome these obstacles, we have developed a novel growth method for obtaining a high-quality hexagonal, well-defined, and vertical 1D Gd-doped n-ZnO nanotube (NT) array deposited on p-GaN films and other substrates by pulsed laser deposition. By adopting this approach, the desired high optical and structural quality is achieved without utilizing metal catalyst. Transmission electron microscopy measurements confirm that gadolinium dopants in the target form a transparent in situ interface layer to assist in vertical NT formation. Microphotoluminescence (PL) measurements of the NTs reveal an intense ZnO band edge emission without a defect band, indicating high quality. Carrier dynamic analysis via time-resolved PL confirms that the emission of n-ZnO NTs/p-GaN LED structure is dominated significantly by the radiative recombination process without efficiency droop when high carrier density is injected optically. We developed an electrically pumped UV Gd-doped ZnO NTs/GaN LED as a proof of concept, demonstrating its high internal quantum efficiency (>65%). The demonstrated performance of this cost-effective UV LED suggests its potential application in large-scale device production.

2024, TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES, AEROSPACE TECHNOLOGY JAPAN

which is a candidate mission of Epsilon Launch Vehicle, plans to execute scientific observations using instruments with the mass of up to about 10 kg on the transfer and Halo orbit of the sun to earth Lagrangian point L1/L2 or on the fly-by orbit of near earth objects (NEO). Potential scientific objects include in-situ observation and remote sensing from these space are solar system explorations, such as, the observations of plasma and energetic particles around the terrestrial magnetosphere, inter-planetary and inter-stellar dust, and NEO. It is also considered to be useful for the pilot observations for future infrared, gamma-ray, and cosmic-ray space astronomical telescope in the deep space. Applied missions of DESTINY will be able to go to deep space with higher mass of payloads. Using the Epsilon Launch Vehicle, it will convey instruments of up to 50 kg to the space between Venus and Mars. DESTINY launched by the improved launch vehicle with the power of M-V rocket will carry payloads of up to 200 kg into the orbit of Venus and Mars. In these phases, Explorations for Venus, Mars, and multiple NEO, and astronomical observations from the deep space observatory will be realized by low cost deep space missions.

2024, Research Square (Research Square)

In this study we suppressed the parasitic emission caused by electron over ow found in typical UVB lightemitting diodes (LEDs). Furthermore, modulation of the player structure and doping pro le allowed us to decrease the relaxation time of the holes to reach conditions of quasi-charge neutrality in the UVB quantum well. Our UVB LED (sample A) exhibited a clear exciton emission, with its peak near 306 nm and a band-to-band emission at 303 nm. The relative intensity of the exciton emission of sample A decreased as a result of a thermal energy effect. At temperatures of up to 363 K, sample A displayed the exciton emission. Our corresponding UVC LED (sample B) exhibited only a Gaussian peak emission at a wavelength of approximately 272 nm.

2024

In this study we suppressed the parasitic emission caused by electron overflow found in typical UVB light-emitting diodes (LEDs). Furthermore, modulation of the p-layer structure and doping profile allowed us to decrease the relaxation time of the holes to reach conditions of quasi-charge neutrality in the UVB quantum well. Our UVB LED (sample A) exhibited a clear exciton emission, with its peak near 306 nm and a band-to-band emission at 303 nm. The relative intensity of the exciton emission of sample A decreased as a result of a thermal energy effect. At temperatures of up to 363 K, sample A displayed the exciton emission. Our corresponding UVC LED (sample B) exhibited only a Gaussian peak emission at a wavelength of approximately 272 nm.

2024

This work presents an experimental and theoretical insight into formation mechanisms of single crystalline wurtzite InN quantum dots (QDs) fabricated via metal droplet epitaxy (DE) by employing plasma assisted molecular beam epitaxy. The applied procedure consists of two fabrication stages. During the first stage, the cold substrate (T % 15°C) is exposed to an impinging In flux, resulting in formation of metallic In droplets on the substrate surface, and then to an impinging active nitrogen flux, resulting in In conversion into polycrystalline InN islands. During the second stage, the substrate, which is still kept exposed to active nitrogen, is heated up to T % 300°C, to allow for the reorganization of extended polycrystalline InN islands into groups of independent single-crystalline wurtzite InN QDs. This work provides a detailed experimental insight into both fabrication stages and their qualitative explanations within the scopes of adatom surface kinetics (stage I) and total energy per unit crystal volume minimization (stage II). Finally, the formation mechanisms of InN QDs on the three different substrates (Si(1 1 1), Si (0 0 1) and In 0.3 Ga 0.7 N/Si(1 1 1)) are compared, and also linked to the formation mechanisms of other more studied nanostructures, such as self-assembled GaN/AlN QDs and self-assembled and selectivearea-grown GaN nanowires.

2024

Les diodes electroluminescentes (DEL) a base de GaN ont deja ete commercialisees comme solution economique d’eclairage, etant donne que les multi-puits quantiques (MQW) bases sur InGaN/GaN peuvent etre concus pour produire de la lumiere dans toute la gamme spectrale visible. Pour obtenir une emission de lumiere blanche, la conversion a base de phosphore conduit a une faible efficacite due a la perte de Stokes et peut egalement produire un faible indice de rendu des couleurs (IRC). Par consequent, pour une efficacite elevee et une lumiere blanche avec un IRC eleve, la generation de lumiere blanche par combinaison rouges-vertes-bleues (RGB) est necessaire. La DEL bleue basee sur InGaN/GaN presente une bonne performance aujourd'hui. La DEL rouge a base de III-phosphure est egalement tres efficace. Cependant, avec des longueurs d'onde intermediaires pour l'emission de spectre vert, l'efficacite des dispositifs diminue avec l'augmentation de la composition d’indium (I...

2023

(COTS) and CubeSat technology. According to Apollo 17 astronaut Gene Cernan, "Dust is probably one of our greatest inhibitors to a nominal operation on the moon." [1] Exposed to bombardment of micrometeoroids, the lunar regolith becomes subjected to miniature shock waves that form sharp glassy fragments called agglutinates, believed to cause hardware failures and to be toxic to astronauts. There is still no effective method of protecting against this abrasive and adhesive dust. [2] During the lunar day, energetic charged particles charge the surface regolith by ejecting secondary electrons from atoms, thus forming positively charged regions. Forces of attraction between these dust particles are mainly horizontal, while the repulsive forces are mainly vertical, creating a dust cloud from the rise of particles. [3] The team proposes that ionizing particles have the ability to also charge surfaces comprised of atoms with low ionization energy. The AMARIS mission will evaluate the potential to repel dust using an ultra-thin lithium nanofoil coating that will be charged positively through ionization for use on instruments, suits, and other equipment. A study by A. P. Jordan outlines a model developed to show the energy levels at which energetic particles strike the lunar surface, causing deep dielectric charging. [4] It takes into account various factors including regolith density, electrical conductivity, permittivity, and the angle of incidence at which the particles hit, determining the depth to which they penetrate. The model demonstrates that the top micrometer of

2023, Plants

Phenolic compounds of 25 newly introduced strawberry cultivars were profiled using spectrophotometry, electron paramagnetic resonance (EPR) spectroscopy, and high-performance liquid chromatography-mass spectrometry. Total phenolic and anthocyanin content (TPC and TACY, respectively), as well as vitamin C, and concentrations of individual phenolic compounds in fruits were evaluated to identify the most promising cultivars according to their phenolic profile. The highest values of TPC, TACY, and vitamin C were recorded in ‘Premy’ (1.53 mg eq GA g−1 FW), ‘Sandra’ (30.60 mg eq Pg-3-g 100 g−1 FW), and ‘Laetitia’ (56.32 mg 100 g−1 FW), respectively. The DPPH and •OH radicals scavenging activity of fruit methanolic extracts was estimated using EPR spectroscopy. All cultivars are almost uniformly effective in the scavenging of •OH radical, while ‘Tea’, ‘Premy’, and ‘Joly’ were marked as highly potent cultivars (over 70%) in terms of DPPH-antiradical activity. Specific peroxidase activities ...

2023, Superlattices and Microstructures

The electronic states are calculated for the asymmetric AlGaAs/GaAs stepped quantum well. The results show a singular behavior of the energy levels as a function of the step layer's width Lw 2. Indeed, we show the existence of plateaus laying within certain Lw 2 intervals. Added to the broken selection rules, this offers more frequency modulation of the intersubband transitions. As a major consequence, there is at least one crossing between two different transitions that occurs for many geometries (at specific Lw 2 widths), which may enhance the optical properties (absorption and emission) in unipolar based devices. We have, then, performed the calculation of the optical absorption coefficient, in order to evaluate the response of such specific structures to an electromagnetic radiation, especially in the terahertz (THz) domain. The calculations are performed for a particular structure where a double two-photon absorption (TPA) may occur. The first TPA corresponds to the E 12 and E 24 transitions crossing at 70meV (17THz) and the second to the crossing of E 23 and E 34 transitions at 35meV (8.5THz).

2023

Purpose-This study aims to present a numerical study of atomic structure for aluminium nitride (AlN) when the crystal was assumed grown on different orientation of sapphire substrate. The change of the AlN atomic structure with sapphire orientation was associated to the interface between the AlN and the sapphire. The results from this study would provide a guideline in selecting suitable orientation of sapphire for obtaining desirable AlN crystals, in particular, for reducing threading dislocation density in the AlN/sapphire templates for developing UV LEDs. Design/methodology/approach-The approach of atomic structure by visualization for electronic and structural analysis numerical method to develop shape of atomic geometry to evaluate which plane are more suitable for the AlGaN technology UV-LED based. Findings-The calculation based on ratio on first and second layers can be done by introduction of lattice constant. Research limitations/implications-With plane's color of cutting plane on bulky materials, all the shape looks the same. Practical implications-By implementing this method, the authors can save time to find the most suitable plane on the growth structure.

2023, Journal of Crystal Growth

Material quality is a critical factor which determines the performance, particularly the open-circuit voltage, of multiple quantum well (MQW) solar cells. In this study, we report an electroluminescence-based characterization technique for evaluating luminescence efficiency and Shockley-Read-Hall recombination lifetime in MQW structures as a measure of the material quality. As a demonstration, various structures of InGaAs/GaAsP MQWs inserted in GaAs solar cells are investigated. The complete compensation of strain and the insertion of GaAs interlayers between heterointerfaces result in significant improvement of electroluminescence homogeneity, external luminescence efficiency, and lifetime, agreeing well with the tendency of the open-circuit voltage. We show that this characterization technique can detect even subtle degradations, which are not easily detectable by other typical techniques, such as in-situ reflection, X-ray diffraction, and spectral and transient photoluminescence, but still have a significant impact on the performance of solar cells.

2023, AIP Advances

III-nitride light-emitting diodes (LEDs) exhibit an injection-dependent emission blueshift and linewidth broadening that is severely detrimental to their color purity. By using first-principles multi-scale modeling that accurately captures the competition between polarization-charge screening, phase-space filling, and many-body plasma renormalization, we explain the current-dependent spectral characteristics of polar III-nitride LEDs fabricated with state-of-the-art quantum wells. Our analysis uncovers a fundamental connection between carrier dynamics and the injection-dependent spectral characteristics of light-emitting materials. For example, polar III-nitride LEDs offer poor control over their injection-dependent color purity due to their poor hole transport and slow carrier-recombination dynamics, which forces them to operate at or near degenerate carrier densities. Designs that accelerate carrier recombination and transport and reduce the carrier density required to operate LED...

2023, SPIE Proceedings

The ultraviolet (UV) window has been largely unexplored through balloons for astronomy. We discuss here the development of a compact near-UV spectrograph with fiber optics input for balloon flights. It is a modified Czerny-Turner system built using off-the-shelf components. The system is portable and scalable to different telescopes. The use of reflecting optics reduces the transmission loss in the UV. It employs an image-intensified CMOS sensor, operating in photon counting mode, as the detector of choice. A lightweight pointing system developed for stable pointing to observe astronomical sources is also discussed, together with the methods to improve its accuracy, e.g. using the in-house build star sensor and others. Our primary scientific objectives include the observation of bright Solar System objects such as visible to eye comets, Moon and planets. Studies of planets can give us valuable information about the planetary aurorae, helping to model and compare atmospheres of other planets and the Earth. The other major objective is to look at the diffuse UV atmospheric emission features (airglow lines), and at column densities of trace gases. This UV window includes several lines important to atmospheric chemistry, e.g. SO 2 , O 3 , HCHO, BrO. The spectrograph enables simultaneous measurement of various trace gases, as well as provides better accuracy at higher altitudes compared to electromechanical trace gas measurement sondes. These lines contaminate most astronomical observations but are poorly characterized. Other objectives may include sprites in the atmosphere and meteor flashes from high altitude burnouts. Our recent experiments and observations with high-altitude balloons are discussed.

2023, Journal of Physical Chemistry C

The Energy Frontier Research Center (EFRC) for Solid-State Lighting Science (SSLS) is one of 46 EFRCs initiated in 2009 to conduct basic and use-inspired research relevant to energy technologies. The overarching theme of the SSLS EFRC is the exploration of energy conversion in tailored photonic structures. In this article we review highlights from the research of the SSLS EFRC. Major research themes include: studies of the materials properties and emission characteristics of III-nitride semiconductor nanowires; development of new phosphors and II−VI quantum dots for use as wavelength downconverters; fundamental understanding of competing radiative and nonradiative processes in current-generation, planar light-emitting diode architectures; understanding of the electrical, optical, and structural properties of defects in InGaN materials and heterostructures; exploring ways to enhance spontaneous emission through modification of the environment in which the emission takes place; and investigating routes such as stimulated emission that might outcompete nonradiative processes.

2023, Applied Surface Science

We report the growth of lower aspect ratio, nano-island shaped, lower stress and strain facilitated gallium nitride nanostructures (GaN-NS) on Si (111) substrate via plasma assisted molecular beam epitaxy (PA-MBE) and fabrication of GaN-NS based UV photodetection device even with NS's tiny dimensionality. GaN-NS were grown on Si (111) substrate with an inhomogeneous layer of Si 3 N 4 which act as anti-surfactant to Ga atoms and also offer localized compressive strain. The developed strain can be relaxed by the growth of inhomogeneously oriented GaN NS. The three dimension (3D) growth of GaN-NS in real time was observed by in-situ RHEED technique which displays transformation from streaky to spotty pattern. A micro-Raman technique has been employed to elaborate NS's crystallinity and lower stress value which is found be in good agreement with related lower strain as evaluated by HR-XRD spectra. A sharp near band edge emission at 363.2 nm is observed by room temperature photoluminescence measurement which signifies the presence of GaN. Metal semiconductor metal Au-GaN-NS/Si(111) device was fabricated to specifically analysed its ability to detect harmful ultraviolet radiations (325nm) with GaN islands of just 26nm height and 50nm width. The performance of the fabricated device was analysed at fixed optical power of 13mW with varying bias voltages (0.4-3V).

2023, Bioprocess and Biosystems Engineering

2023, SPIE Proceedings

The Australian Space Eye is a proposed astronomical telescope based on a 6 U CubeSat platform. The Space Eye will exploit the low level of systematic errors achievable with a small space based telescope to enable high accuracy measurements of the optical extragalactic background light and low surface brightness emission around nearby galaxies. This project is also a demonstrator for several technologies with general applicability to astronomical observations from nanosatellites. Space Eye is based around a 90 mm aperture clear aperture all refractive telescope for broadband wide field imaging in the i and z bands.

2023, Applied Sciences

Visible Light Communication (VLC) technology is an emerging technology using visible light modulation that, in the modern world, will mainly facilitate high-speed internet connectivity. VLC provides tremendous advantages compared to conventional radio frequency, such as a higher transmission rate, high bandwidth, low-power consumption, no health hazards, less interference, etc., which make it more prominent in recent days. Due to their outstanding features, including low cost, low power consumption, etc., µ-light-emitting diodes (LEDs) have gained considerable attention for VLC implementation, but mostly for the ability to be used for lighting as well as communications. In this review paper, we will focus mainly on recent developments in VLC applications and various factors affecting the modulation bandwidth of VLC devices. Numerous factors, such as quantum confined stark effect (QCSE), carrier lifetime, carrier recombination time, crystal orientation, etc. affect the modulation ban...

2023, arXiv (Cornell University)

Ultra-wide bandgap (UWBG) materials are poised to play an important role in the future of power electronics. Devices made from UWBG materials are expected to operate at higher voltages, frequencies, and temperatures than current silicon and silicon carbide based devices; and can even lead to significant miniaturization of such devices. In the UWBG field, aluminum nitride and boron nitride have attracted great interest, however, the BxAl1−xN alloys are much less studied. In this article, using first-principles simulations combining density-functional theory and the cluster expansion method we predict the crystal structure of BxAl1−xN alloys. We find 17 ground state structures of BxAl1−xN with formation energies between 0.11 and 0.25 eV/atom. All of these structures are found to be dynamically stable. The BxAl1−xN structures are found to have predominantly a tetrahedral bonding environment, however, some structures exhibit sp 2 bonds similar to hexagonal BN. This work expands our knowledge of the structures, energies, and bonding in BxAl1−xN which aids their synthesis, the innovation of lateral or vertical devices, and discovery of compatible dielectric and Ohmic contact materials.

2023, Master-Thesis

Sonic Tractions. The sound art by Emeka Ogboh, and Ultra-red in the struggle against gentrification.

2023, Applied Physics Letters

Space charge profile study of AlGaN-based p-type distributed polarization doped claddings without impurity doping for UV-C laser diodes

2023

This paper sets out to show the in-flight results of The Netherlands-China Low-Frequency Explorer (NCLE) – one of the first times CubeSat hardware has left low Earth Orbit. The Netherlands-China Low-Frequency Explorer (NCLE), is a low-frequency payload which is part of the Chinese Chang’e 4 mission. The NCLE instrument consists of three 5-meter long monopole antennas mounted on the Queqiao satellite and will be measuring in the 80 kHz 80 MHz radio frequency range. The instrument is designed to address a multitude of high-profile science cases, but predominantly NCLE will open up the low-frequency regime for radio astronomy and will prepare for the ground-breaking observations of the 21-cm line emission from the Dark Ages and the Cosmic Dawn, considered to be the holy grail of cosmology. The design of the instrument began in May 2016, with a launch scheduled May 2018. This left only 2 years to develop, build and test the instrument. Given the short development time the design is base...

2023

Optoelectronics (e.g., light-emitting diodes, photodetectors) is one of the most widely used fields nowadays. But it is still necessary to improve their characteristics for using in general lighting. In this chapter, the heterostructure conductivity type, impurity and indium atoms influence on the LEDs and phototransistor characteristics are investigated by computer simulation. It was found that current-voltage characteristic and quantum efficiency depend on impurity and indium atoms change a lot. By varying impurity and indium atom concentration, controlling their distribution in InGaN and AlGaP heterostructure LEDs and photodetector characteristics can be improved.

2023, physica status solidi c

The influence of built-in piezoelectric field in the lightemitting diodes based on InGaN/AlGaN/GaN heterostructures on the electroreflectance spectra have been studied. The structures were grown by MOCVD technology and «flipchip» mounted. The spectral line connected with the InGaN/GaN multiple quantum wells region are observed in the electroreflectance spectra. The blue shift of this spectral line with the increasing reverse bias voltage has been explained as the result of decreasing of the electric field in the quantum well.

2023, Physics Education

Solar current is an increasingly important aspect of modern life and will be even more so crucial in the students' future. Encouraging students to be the 'toolmakers' allows students to take ownership of scientific investigations, as well as forcing them to refine their research questions and hypothesis the design and refinement of their tools. The modern day has seen an unprecedented opportunity for toolmaking, in the form of adapting and programming apps that use the micro-electro-mechanical sensors that are an intrinsic part of smartphone technology. A sample in-class experiment and an experimental investigation are presented; these represent an increase in toolmaking and student ownership with a corresponding decrease in teacher guidance. Toolmaking progresses from the construction of a physical sunspotter, using a hand lens and cutoff tube, using apps, to future considerations such as programming, adapting pre-existing code samples to be able to manipulate the smartphone sensors.

2023, Nanotechnology

Developing single-nanowire terahertz (THz) electronics and employing them as sub-wavelength components for highly-integrated THz time-domain spectroscopy (THz-TDS) applications is a promising approach to achieve future low-cost, highly integrable and high-resolution THz tools, which are desirable in many areas spanning from security, industry, environmental monitoring and medical diagnostics to fundamental science. In this work, we present the design and growth of n(+)-i-n(+) InP nanowires. The axial doping profile of the n(+)-i-n(+) InP nanowires has been calibrated and characterized using combined optical and electrical approaches to achieve nanowire devices with low contact resistances, on which the highly-sensitive InP single-nanowire photoconductive THz detectors have been demonstrated. While the n(+)-i-n(+) InP nanowire detector has a only pA-level response current, it has a 2.5 times improved signal-to-noise ratio compared with the undoped InP nanowire detector and is compara...

2023, Nanotechnology

2023, Japanese Journal of Applied Physics

The nitride semiconductor materials GaN, AlN, and InN, and their alloys and heterostructures have been investigated extensively in the last 3 decades, leading to several technologically successful photonic and electronic devices. Just over the past few years, a number of “new” nitride materials have emerged with exciting photonic, electronic, and magnetic properties. Some examples are 2D and layered hBN and the III–V diamond analog cBN, the transition metal nitrides ScN, YN, and their alloys (e.g. ferroelectric ScAlN), piezomagnetic GaMnN, ferrimagnetic Mn4N, and epitaxial superconductor/semiconductor NbN/GaN heterojunctions. This article reviews the fascinating and emerging physics and science of these new nitride materials. It also discusses their potential applications in future generations of devices that take advantage of the photonic and electronic devices eco-system based on transistors, light-emitting diodes, and lasers that have already been created by nitride semiconductors.

2023, Optical Materials

A deep ultraviolet light-emitting diode (DUV LED) consisting of a specifically designed intermediate p-type region involving a superlattice quaternary nitride alloy has been proposed. The light output power of the proposed structure has been found significantly large; around 28.30 times high in comparison to the conventional structure, at the current density of 200 A/cm 2. The maximum internal quantum efficiency of the proposed structure is 153.63% higher compared to the conventional one. Moreover, the efficiency droop has been reduced by 99.08%. Absence of abrupt potential barrier owing to the strain compensation provided by the superlattice p-AlInGaN layer offers an attractive solution for enhancing the hole injection into the active region leading to the improvement in performance of DUV LED.

2023, Physical Review Letters

White light emitting diodes based on III-nitride InGaN/GaN quantum wells currently offer the highest overall efficiency for solid state lighting applications. Although current phosphor-converted white LEDs have high electricity-to-light conversion efficiencies, it has been recently pointed out that the full potential of solid state lighting could be exploited only by color mixing approaches without employing phosphor-based wavelength conversion. Such an approach requires direct emitting LEDs of different colors, in particular in the green/yellow range ov the visible spectrum. This range, however, suffers from a systematic drop in efficiency, known as the "green gap", whose physical origin has not been understood completely so far. In this work we show by atomistic simulations that a consistent part of the "green gap" in c-plane InGaN/GaN based light emitting diodes may be attributed to a decrease in the radiative recombination coefficient with increasing Indium content due to random fluctuations of the Indium concentration naturally present in any InGaN alloy.

2023, Optoelectronics - Advanced Device Structures

2023, Experimental Astronomy

Observing the ultraviolet (UV) sky for timevaryiable phenomena is one of the many exciting science goals that can be achieved by a relatively small aperture telescope in space. The Near Ultraviolet Transient Surveyor (NUTS) is a wide-field (3 •) imager with a photoncounting detector in the near-UV (NUV, 200-300 nm), to be flown on an upcoming small satellite mission. It has a Ritchey-Chrétien (RC) telescope design with correction optics to enable wide-field observations while

2023, Physi Rev B

Slides by C.Jayant Praharaj on Instantons for Optically-Generated Quantum Entanglement in InGaN Quantum Dots

2023, Nature Communications

On-chip plasmonic circuitry offers a promising route to meet the ever-increasing requirement for device density and data bandwidth in information processing. As the key building block, electrically-driven nanoscale plasmonic sources such as nanoLEDs, nanolasers, and nanojunctions have attracted intense interest in recent years. Among them, surface plasmon (SP) sources based on inelastic electron tunneling (IET) have been demonstrated as an appealing candidate owing to the ultrafast quantum-mechanical tunneling response and great tunability. However, the major barrier to the demonstrated IET-based SP sources is their low SP excitation efficiency due to the fact that elastic tunneling of electrons is much more efficient than inelastic tunneling. Here, we remove this barrier by introducing resonant inelastic electron tunneling (RIET)—follow a recent theoretical proposal—at the visible/near-infrared (NIR) frequencies and demonstrate highly-efficient electrically-driven SP sources. In ou...

2023, IEEE Transactions on ED

Slides by C.Jayant Praharaj on Quantum Ergodicity and Quasi-Ergodicity in Scaled InGaN Devices

2023

We explore the effect of the subwell centers and related carrier dynamics mechanisms in dislocation-free DUV AlGaN/AlGaN multiple quantum wells (MQWs) homoepitaxially grown on an AlN substrate. Cross-sectional imaging and energydispersive X-ray compositional analyses using scanning transmission electron microscopy (STEM) reveal epitaxial layers of very high crystalline quality, as well as ultrathin Al-rich subquantum barrier and subwell layers at the interface between the wells and the barriers. Carrier dynamic analyses studied by power-and temperature-dependent time-resolved and time-integrated photoluminescence (PL) and PL excitation measurements, as well as numerical simulations, reveal the carrier repopulation mechanisms between the MQWs and subwell sites. This advanced analysis shows that the subwell/sub-barrier structure results in additional exciton localization centers, enhancing the internal quantum efficiency via staggered carrier repopulation into the MQWs to reach a maximum of ∼83% internal quantum efficiency, which remains high at high injected carrier densities in the droop region. Both experimental and numerical simulation results show that the slight efficiency droop can be due to Auger recombination, counteracted by a simultaneous increase in radiative recombination processes at high power density, demonstrating the role of the subwells/sub-barriers in efficiency enhancement.

2023, IEEE Transactions on Electron Devices

Slides by C.Jayant Praharaj on Semiconductor Physics for Ultrafast Electronics - Polarization and High-Speed Transport

2023, Instrumentation Science & Technology

A method for determining the dark response for scientific imaging with smartphones.

2023, Journal of Crystal Growth

Deep ultraviolet (UV) emission at 260nm has been obtained from high Al conetent AlGaN/AlN multi-quantum well (MQW) structures by plasma-assisted molecular beam epitaxy (PA-MBE) on AlN template on sapphire substrates. The effect of III/V ratio and growth temperature on structural and optical properties of AlGaN was studied. It was observed that Al content in AlGaN material increased with increasing Al flux ratio or growth temperature. By altering growth conditions, AlGaN with high Al content of 47% ~ 80% was obtained. Further studies indicate that AlGaN layers have excellent surface morphology and optical properties grown in slightly metal-rich condition. As for AlGaN/AlN MQW, the emission wavelength was tuned by controlling the thickness of AlGaN quantum well, and deep ultraviolet emission below up to 260 nm was obtained from AlGaN (2.4 nm)/AlN(6.9 nm) MQW at room temperature.

2023, Applied Physics Letters

Electron paramagnetic resonance studies of Si-doped Al x Ga 1Àx N (0.79 x 1.0) reveal two Si negative-U (or DX) centers, which can be separately observed for x ! 0.84. We found that for the stable DX center, the energy jE DX j of the negatively charged state DX À , which is also considered as the donor activation energy, abruptly increases with Al content for x $ 0.83-1.0 approaching $240 meV in AlN, whereas E DX remains to be close to the neutral charge state E d for the metastable DX center