Electrically injected deep ultra-violet emission is obtained using monolayer thin GaN/AlN quantum structures as active regions. The emission wavelength is tuned by controlling the thickness of ultrathin GaN layers with monolayer precision using plasma assisted molecular beam epitaxy. Single peaked emission spectra are achieved with narrow full width at half maximum for three different light emitting diodes operating at 232 nm, 246 nm, and 270 nm. 232 nm (5.34 eV) is the shortest electroluminescence (EL) emission wavelength reported so far using GaN as the light emitting material and employing polarization-induced doping.

Irradiation with deep-ultraviolet light-emitting diodes (DUV LEDs) is emerging as a low energy, chemical-free approach to mitigate microbial contamination, but the effect of surface conditions on treatment effectiveness is not well understood. Here, inactivation of L. innocua and E. coli ATCC25922, as examples of Gram-positive and Gram-negative bacteria, respectively, by DUV LED of 280 nm wavelength was studied. Surface scenarios commonly encountered in environmental, clinical or food processing environments were used: nutrient rich surfaces, thin liquid films (TLF), and stainless steel surfaces (SS). DUV LED exposure achieved 5-log reduction for both strains within 10 min in most scenarios, except for TLF thicker than 0.6 mm. Inactivation kinetics in TLF and on dry SS followed the Weibull model (0.96 ≤ R 2 ≤ 0.99), but the model overestimated inactivation by small-dose DUV on wet SS. Confocal microscopy revealed in situ that bacteria formed a dense outer layer at the liquid-air interface of the liquid droplet, protecting the cells inside the droplet from the bactericidal DUV. This resulted in lower than anticipated inactivation on wet SS at small DUV doses, and deviation from the Weibull model. These findings can be used to design effective DUV LED disinfection strategies for various surface conditions and applications. Persistence of pathogens on material surfaces often causes severe consequences, including infections in dental offices and hospitals 1 , or transfer of pathogenic or spoilage microorganisms from food contact surfaces to food products in food processing facilities and food service environments 2. Exposing surfaces contaminated by microorganisms to ultraviolet (UV) of wavelength 100-280 nm has been established as an effective disinfection method, often used as an alternative to or in tandem with chemical disinfection methods. Mercury lamps are currently the most commonly used source of UV light. Yet, according to the Minamata Convention on Mercury 3 , signed in 2013, manufacturing and trading of mercury-containing lamps for general lighting purposes will be disallowed after 2020, to reduce and eliminate the adverse effects of mercury on human health and the environment. This agreement accelerated the efforts for the development of alternatives to mercury lamps. Light-emitting diodes that emit light in the UV range (UV LEDs) present several advantages compared to mercury lamps, including the lack of toxic mercury, device compactness and flexible designs, zero warm-up time 4,5 , high durability, monochromatic light emission at specific wavelength 6 , wavelength diversity, possibility of pulsed illumination, and the capability of maintaining relatively high activity at cold temperatures (e.g. refrigeration) 5. UV LEDs are also known for their low heat emission in the form of IR radiation 7 , which enables applications that demand high UV fluence while preventing heating over long periods of time. Recent progress in improving the light-extraction efficiency of UV LEDs in the range 200-300 nm has increa...

The frozen internal polarization-induced electric fields due to broken inversion symmetry in all conventional blue and green nitride semiconductor light emitting semiconductor quantum well heterostructures point in a direction opposite to what is desired for efficient flow of electrons and holes. This state of affairs has persisted because of the desire to have p-type hole injectors on top of the quantum well active region. Because of the internal polarization fields in nitride heterostructures, there exist four permutations of doping and polarization for the realization of such light emitters. Which permutation is the most desirable for efficient light emission? In this work, we answer this question by demonstrating a fundamentally new approach towards efficient light emission with bottom-tunnel junctions. The bottomtunnel junction design aligns the polarization fields in a desired direction in the quantum well, while simultaneously eliminating the need for p-type contacts, and allowing efficient current spreading. By preventing electron overshoot past quantum wells, it disables carrier recombination in undesired regions of the quantized heterostructures, and opens up the possibility for new geometries of integrating and stacking multiple light emitters. Due to the inherent advantages, the bottom-tunnel junction light emitting diode enables a 200-300% increase in the light emission efficiency over alternate heterostructure designs.

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We report optically and electrically pumped ∼ 280 n m deep ultraviolet (DUV) light emitting diodes (LEDs) with ultra-thin GaN/AlN quantum disks (QDs) inserted into AlGaN nanorods by selective epitaxial regrowth using molecular beam epitaxy. The GaN/AlN QD LED has shown strong DUV emission distribution on the ordered nanorods and high internal quantum efficiency of 81.2%, as a result of strain release and reduced density of threading dislocations revealed by transmission electron microscopy. Nanorod assembly suppresses the lateral guiding mode of light, and light extraction efficiency can be increased from 14.9% for planar DUV LEDs to 49.6% for nanorod DUV LEDs estimated by finite difference time domain simulations. Presented results offer the potential to solve the issue of external quantum efficiency limitation of DUV LED devices.