We demonstrate the application of atom probe tomography for assessing the crystalline orientation of nanoscale semiconductor structures via the analysis of charge state ratio maps in the detector space. The experimental realization is carried out in the context of adventitious cone-shaped domains present in AlGaN quantum dot superlattices. The cone-shaped domains, which emerge from shallow pits generated in AlN and propagate through the superlattices, are shown to exhibit small misorientation angles of their crystalline 〈0001〉 poles. The results of the atom probe tomography analysis are confirmed by convergent beam electron diffraction measurements. The use of this methodology adds another layer to the application of this technique to semiconductor nanoscale systems, providing not only compositional maps but also information on the crystallographic orientation.

We study the origin of bimodal emission in AlGaN/AlN QD superlattices displaying a high internal quantum efficiency (around 50%) in the 230-300 nm spectral range. The secondary emission at longer wavelengths is linked to the presence of cone-like domains with deformed QD layers, which originate at the first AlN buffer/superlattice interface and propagate vertically. The cones originate at a 30 degrees-faceted shallow pit in the AlN, which appears to be associated with a threading dislocation that produces strong shear strain. The cone-like structures present Ga enrichment at the boundaring facets and larger QDs within the conic domain. The bimodality of the luminescence is attributed to the differing dot size and composition within the cones and at the faceted boundaries, which is confirmed by the correlation of microscopy results and Schrodinger-Poisson calculations.

We study the origin of bimodal emission in AlGaN/AlN QD superlattices displaying high internal quantum efficiency (around 50%) in the 230-300 nm spectral range. The secondary emission at longer wavelengths is linked to the presence of cone-like defects starting at the first AlN buffer/superlattice interface and propagating vertically. These defects are associated with a dislocation that produces strong shear strain, which favors the formation of 30{\deg} faceted pits. The cone-like structures present Ga enrichment at the boundary facets and larger QDs within the defect. The bimodality is attributed to the differing dot size/composition within the defects and at the defect boundaries, which is confirmed by the correlation of microscopy results and Schr\"odinger-Poisson calculations.

Conventional ultraviolet (UV) lamps for disinfection emit radiation in the 255-270 nm range, which poses a high risk of causing cancer and cataracts. To address these concerns, solid-state far UV-C sources emitting below 240 nm are gaining attention as a safe and sustainable disinfection solution for occupied spaces. Here, we delve into the extension of the AlxGa1-xN/AlN quantum dot (QD) technology towards the far UV-C range, which presents various challenges associated with the reduction of the lattice mismatch and band offset when Al is incorporated in the QDs. We explore the structural and optical impact of increasing the Al content through the increase of the Al flux and eventual correction of the Ga flux to maintain a constant metal/N ratio. We also examine the impact of extreme miniaturization of the QDs, achieved through a reduction of their growth time, on the spectral behavior and internal quantum efficiency (IQE). The high Al content results in QDs with a reduced aspect ratio (height/diameter) and thicker wetting layer when compared to the GaN/AlN system. Self-assembled QDs grown with a metal/N ratio ranging from 0.5 to 0.8 show an IQE around 50%, independent of the Al content (up to 65%) or emission wavelength (300-230 nm). However, samples emitting at wavelengths below 270 nm exhibit a bimodal luminescence associated with inhomogeneous in-plane emission attributed to fluctuations of the QD shape associated with extended defects. Reducing the QD size exacerbates the bimodality without reducing the emission wavelength. The power efficiencies under electron beam pumping range from 0.4% to 1%, with clear potential for improvement through surface treatments that enhance light extraction efficiency.

Ultraviolet GaN photodetectors based on nanowires (NWs)fabricatedby top-down strategies promise improved uniformity, morphology, anddoping control with respect to bottom-up ones. However, exploitingthe advantages of the NW geometry requires sub-wavelength NW diameters.We present fabrication of large-area sub-200 nm diameter top-downGaN p-i-n NW ultraviolet photodetectors with lengths over 2 & mu;m producedfrom a planar specimen using nanosphere lithography, followed by acombination of dry and crystallographic-selective wet etching. Photocurrentmeasurements in single-NW devices under bias show a linear responseas a function of the optical power, with increased current levelsunder reverse bias. The linearity proves that the drift of photogeneratedcarriers at the junction is the dominating photodetection mechanism,with negligible contributions from surface effects. These resultsdemonstrate that the unique properties of NW-based photodetectorscan be assessed through a scalable and low-cost fabrication process.

Recently, there has been an increased interest in germicidal ultraviolet (GUV) lamps for disinfection. Despite extensive studies on GUV LEDs, their efficiency and cost per Watt is still far from that of mercury lamps due to electrical injection issues, among others. Also, the fact that 254 nm radiation is highly carcinogenic and cataractogenic, has motivated research on radiation with shorter penetration (200-230 nm) depth, for non-invasive disinfection. In this study, we propose electron pumped UV lamps as an alternative to LEDs (to tackle electrical issues) in the spectral range 230-330 targeting both wavelength ranges of disinfection and exhibiting IQE ranging from 20%-50%.

Electron beam pumping is a promising technique to fabricate compact and efficient light emitters (lamps or lasers) in those spectral ranges where electrical injection is problematic due to doping, transport or contacting issues. Interest in this technology has increased in recent years, particularly driven by the demand for ultraviolet sources and the difficulties in developing efficient AlGaN devices to cover the spectral range of 220–350 nm. The use of a highly energetic electron beam enables the semiconductor structure to be pumped without the need for doping or contacting. The active volume is defined by the acceleration voltage, which allows the homogeneous excitation of a large active volume. The efficiency of cathodoluminescent lamps can compete and even outperform light emitting diode in the deep ultraviolet window, and lasers can deliver high optical power (up to around 100 W). Here, we analyze the advantages and challenges of this technology platform, and discuss its potential applications.

There is a soaring demand for UV lamps emitting at 220-270 nm for applications in disinfection. These needs are currently met by mercury lamps, hazardous for heath and the environment. Despite intense studies on UV LEDs, their efficiency remains limited by problems related to electrical injection. Here, we propose electron pumped UV lamps as an alternative to LEDs in this spectral range. For this purpose, superlattices of close-packed self-assembled AlGaN quantum dots are particularly promising, due to their high internal quantum efficiency (around 50%) and promising external quantum efficiency (4% in as-grown material, increasing to 7% by dice polishing).

The emergence of 2D materials has gained immense attention for photocatalytic applications due to their thickness dependent physical and chemical properties. In this paper, MoS2 nanosheets were synthesized by low cost hydrothermal method. The sample was well characterized by X-ray diffraction (XRD) and UV-Vis spectroscopy and scanning electron microscopy (SEM) micrographs confirm the formation of MoS2 ultra-thin nanosheets. A deep and extensive photocatalytic comparative study is performed on bulk MoS2 with hydrothermally synthesized MoS2 nanosheets under the sunlight by the degradation of methylene blue (MB) dye.

Acetylcholine (ACh) present inside the brain has ability to alter neuronal activation, influencing transmission of synapse by inducing neurons causing the enhancement in the ability of neuronal networks inside the brain. In result, ACh modifies the response of internal and external environment and perform function as a neuromodulator. This empowers the plan of a sensor particular for ACh that is effectively brought into biological frameworks. The work described here, an acetylcholinesterase (AChe) based sensor which is the most promising tool for analysis of neuromodulator level in biological samples. The prepared biosensor interface is based on co-immobilization of the AChe and choline oxidase (Cho) onto palladium nanoparticles (Pd-nano) adsorbed over molybdenum disulfide (MoS2) nanostructures electrodeposited on the surface of gold electrode (Au-ET). The sensor had excellent linear range of 1.0 nM to 10 niM with 1.0 nM as limit of detection. The novel AChe-Cho/Pdnano/MoS2@Au-ET shows a tremendous potential for applications in medical research and clinical diagnosis. The novel biosensor formed has good accuracy, precision and reliability hence, it might provide a new outlook for the detection and recognition of ACh in real serum samples.

This article describes the fabrication of nitrogen‐polar AlxGa1−xN/AlN (x = 0, 0.1) quantum dot (QD) superlattices (SLs) integrated along GaN nanowires (NWs) for application in electron‐pumped UV sources. The NWs are grown using plasma‐assisted molecular beam epitaxy on n‐type Si(111) wafers using a low‐temperature AlN nucleation layer. Growth conditions are tuned to obtain a high density of noncoalesced NWs. To improve the uniformity of the height along the substrate, the growth begins with a long (≈900 nm) NW base, with a diameter of 30–50 nm. The AlxGa1−xN/AlN active region is 400 nm long (88 periods of QDs), long enough to collect the electron–hole pairs generated by an electron beam with an acceleration voltage ≤5 kV. The spectral response is tuned in the 340–258 nm range by varying the dot/barrier thickness ratio and the Al content in the dots. Internal quantum efficiencies as high as 63% are demonstrated.

Ce projet est une contribution au développement de lampes ultraviolettes (UV) à haute luminosité, sans mercure, 100 % recyclables et à haute brillance, pour la désinfection à 270 nm. Les performances des LED UV à base d'AlGaN restent limitées par des problèmes d'injection de porteurs, dus à la haute énergie d'activation des dopants dans ce matériau et aux difficultés de mise en œuvre des contacts ohmiques. Pour contourner ces problèmes, nous proposons de pomper une région active à base de nanostructures d'AlGaN avec un faisceau d'électrons. Pour étudier les milieux actifs des lampes UV à pompage électronique pour la désinfection, deux types d'hétérostructures sont considérés, à savoir les boîtes quantiques (BQs) AlGaN/AlN intégrées dans des nanofils (NFs) GaN synthétisés sur des substrats Si(111) et les BQs AlGaN/AlN développées par la méthode Stranski-Krastanov (SK) sur des matrices AlN sur saphir. Ces choix étaient basés sur la haute efficacité quantique interne (IQE) qui peut être atteinte dans les BQ grâce au confinement tridimensionnel des porteurs. La croissance de toutes les structures a été réalisée par épitaxie par jets moléculaires assistée par plasma.La première étape du travail a consisté à établir la faisabilité des BQ dans les NFs pour cette application. Des études structurelles et optiques ont démontré que les dimensions des BQs étaient assez homogènes le long du super-réseau (SR) de 400 nm de long, donnant une seule raie d'émission accordable dans la plage de 340 à 258 nm. Nous avons démontré des niveaux d'IQE supérieurs à 60% à 340 nm à température ambiante, diminuant lors de la réduction de la longueur d'onde d'émission. A 270 nm, l'IQE était d'environ 30 %. Ces valeurs ont été obtenues sous faible injection, mais restent stables pour des densités de pompage jusqu'à 200 kW/cm2. Sous pompage par faisceau d'électrons, les effets de canalisation dus à la géométrie NF peuvent être compensés en augmentant la longueur de la région active de 60 % par rapport aux couches planaires. L'efficacité quantique externe sous pompage optique donne des résultats prometteurs (3,42±0,55%).La deuxième étape du travail a consisté à étudier les SRs de BQs SK AlGaN/AlN. Il est démontré qu'en modifiant le rapport III/V et/ou la composition des BQs, la longueur d'onde d'émission maximale peut être réglée de 225 nm à 335 nm, tout en maintenant l'IQE autour de 50 % dans la gamme 250-335 nm, et plus de 35 % dans la gamme 225-250 nm. L'IQE de ces nanostructures reste stable des densités de puissance d'injection faibles jusqu'à 200 kW/cm2. Un rendement énergétique moyen de 0,38 % est mesuré pour les structures brutes de croissance, et cela sans aucun traitement pour améliorer l'efficacité d'extraction de la lumière ou la gestion thermique. Ces résultats sont très prometteurs pour le développement d'une technologie UV efficace et respectueuse de l'environnement pour la désinfection.