Deep UV LEDs have historically pumped mild by way of the bottom of the chip, or substrate. Guo-Dong Hao, Manabu Taniguchi, Wei Lingjie, and Shinichiro Inoue from the Nationwide Institute of Info and Communications Know-how (NICT) in Kobe have now reported a 275-nm machine that emits mild from the highest and converts as much as 6.5% of enter energy into ultraviolet mild. Their open entry paper was revealed in ACS Photonics, Quantity 13, Problem 21 on November 4, 2026, and is obtainable on-line beginning October 21, 2026.
why is that this vital
Deep ultraviolet LEDs (DUV LEDs) are constituted of aluminum gallium nitride (AlGaN). The authors checklist its use in floor disinfection, air and water purification, meals security, photolithography, UV curing, and sun-blocking communications. LED specialists highlighted one in all them in an article about large-scale water disinfection utilizing deep ultraviolet LEDs.
In response to the paper, all DUV LEDs reported to date are flip-chip. That’s, the chip is flipped over, mounted on one other submount, and emitted by way of the sapphire substrate. This bottom-emitting construction has two drawbacks. Shifting the chip to a submount makes manufacturing extra advanced and expensive. Sapphire additionally has a decrease refractive index (about 1.8) than AlGaN (about 2.2 to 2.6), a lot of the sunshine is mirrored on the boundary between the 2 and stays confined to the semiconductor layer.
Sending the sunshine out from the highest avoids each issues, however the prime of the chip is the place the present enters. To create a low-resistance (ohmic) contact, producers develop a layer of p-type gallium nitride (p-GaN) on prime of it and canopy it with a steel p-electrode. Each strongly take in deep ultraviolet mild. Clear conductive supplies are usually not out there even at these wavelengths, so top-emitting DUV LEDs haven’t been realized.
What the researchers did
The NICT staff wasn’t on the lookout for a brand new clear contact materials. It builds on the micromesh electrodes the group launched for flip-chip LEDs in 2025, making the contacts translucent by way of their geometry.
- ring-shaped mesa. The mesa is a raised, etched area of the chip that accommodates the light-emitting layer and is a hoop with an interior diameter of 200 μm and an outer diameter of 600 μm. The ring has interior and outer sidewalls, so mild touring laterally contained in the layer can shortly attain the sides and escape from there. The n-electrode is a 180 µm disk within the middle of the ring that absorbs little or no mild touring in direction of the sting of the chip.
- Concentric micro-ring electrodes. A concentric p-electrode ring of nickel and gold with a width of two μm and a pitch of 10 μm is positioned on prime of the mesa. Collectively they cowl about one-fifth of the mesa. The p-GaN stays as a contact layer solely below these rings. Between them there may be an etching, opening a window of sunshine.
- Hafnium oxide nanostructure. Within the window, hafnium oxide (HfO2) truncated cones (flat-topped cones) are organized in a triangular lattice at intervals of 540 nm. Every cone is roughly 200 nm excessive, roughly 200 nm extensive on the prime, and the sidewall angle is roughly 60°. These dimensions have been optimized by optical simulation. The cone magnifies the escape cone, which is a slender vary of angles by way of which mild can go from the semiconductor to the surface.
- rearview mirror. An aluminum layer on the again of the sapphire substrate displays downward mild in direction of the highest.
These layers have been grown on sapphire by metal-organic chemical vapor deposition (MOCVD), a typical development course of for LEDs. The microrings have been outlined by electron beam lithography. The wafer was diced into 1 mm x 1 mm chips, mounted in a TO-CAN package deal (steel can housing), and sealed.
As a reference, the staff constructed a traditional flip-chip LED from the identical wafer with the identical electrode geometry and likewise in contrast top-emitting chips with and with out an HfO2 cone. All gadgets have been measured in DC operation at room temperature utilizing an integrating sphere calibrated for optical output with out exterior thermal administration. The paper doesn’t state the variety of gadgets measured.
Three effectivity phrases are used. Exterior quantum effectivity (EQE) is the variety of photons leaving the machine for every electron provided. Wall plug effectivity (WPE) is the optical output energy divided by {the electrical} enter energy. The authors estimate electrical effectivity by dividing WPE by EQE. Signifies how a lot of the utilized voltage is used.
Most important findings
- A primary for this machine class. The authors name their work “the primary demonstration of a top-emission AlGaN-based DUV LED.” The emission wavelength is 275 nm, the spectral width (FWHM) is 10 nm at 10 mA, and there’s no parasitic emission.
- Wall outlet effectivity. The packaged LED reaches a peak WPE of 6.5% at 7 mA. That is roughly 1.35 instances bigger than the flip-chip reference.
- Exterior quantum effectivity. Peak EQE is 7.5% at 10 mA.
- electrical effectivity. Roughly 85% at 10mA.
- Output energy. 38mW at 200mA.
- mild extraction. Beneath 50 mA, the highest emitter delivers about 1.35 instances the output of the flip-chip reference with the HfO2 cone and about 1.13 instances the output with out the HfO2 cone. Since all gadgets are constituted of the identical wafer, the authors attribute this achieve to improved mild extraction.
- Benefits improve with circulation. The output of 200mA is roughly 2.1 instances that of a flip chip. The authors consider this is because of much less self-heating, and pulse measurements assist this. With the highest emitter, the whole board (1 mm²) is on the package deal, however the flip-chip dissipates warmth solely by way of contact pads with an space of 0.06 mm².
- There isn’t a voltage penalty. The highest emitter and flip chip present the identical current-voltage curve, with turn-on voltages of 4.5V and 6.5V at 100mA, however the p-contact space is diminished.
- completely different beam shapes. The flip chip emits mild in an virtually Lambertian sample, being brightest straight forward and fading evenly to the edges. The highest emitter sends extra mild laterally, and the HfO2 cone displays robust emission at roughly ±40° from the floor regular (measured at 5 mA).
- Even with the present unfold. Close to-field photos at 50 mA present uniform emission throughout the ring mesa, regardless of the small central n-electrode, and robust emission from the interior and outer edges of the mesa on the prime emitter.
What it means for the lighting business
This research reveals that clear p-contact supplies are usually not a prerequisite for top-emission deep UV LEDs. Electrodes that cowl solely one-fifth of the mesa can carry present with out rising the working voltage, and the chip not requires a submount.
In our view, thermal outcomes are simply as vital to product builders as effectivity numbers. Chips with their whole base on the package deal have much less output loss at excessive currents, and on this research, the hole with the flip chip widened from 1.35 instances to about 2.1 instances at 200 mA. How nice this benefit truly is is determined by how the flip chip being changed is applied. The reference thermal contact space right here was solely 0.06 mm².
In our opinion, UV-C module builders also needs to take note of the beam form. Emissions that peak at about ±40° relatively than a Lambertian sample change the necessity for reflector, lens, and reactor chamber layouts, and optics designed for flip-chip emitters can’t be assumed to work unmodified.
Effectivity have to be learn in context. A peak WPE of 6.5% implies that greater than 93% of {the electrical} enter turns into warmth, and the height happens at 7 mA, which is way decrease than the 200 mA at which 38 mW was measured. In our view, this paper is an indication of structure relatively than a file. A novel reference checklist features a 2017 report for 275 nm LEDs with EQE higher than 20%.
The authors consider that eliminating the chip switch step might pave the best way for lower-cost gadgets. In our view, this isn’t but clear. Prices weren’t quantified on this paper, and the microrings on this research have been outlined by electron beam lithography, a time-consuming analysis approach that may must be changed for mass manufacturing. For lighting designers, their work does not have a direct affect. This considerations UV-C sources which will later be utilized in disinfection and curing merchandise.
Restrictions
The paper reveals one chip design at one wavelength and doesn’t say what number of gadgets have been measured. This comparability is with the group’s personal flip-chip LEDs with similar electrode geometries from the identical wafer, isolating architectural results, however just isn’t a benchmark towards one of the best flip-chip gadgets. Lifetime, reliability, and operation at excessive temperatures haven’t been studied, and radiation patterns have been reported solely at low currents of 5 mA. Price advantages are mentioned from the method circulation and are usually not quantified.
citation
Hao, G.-D., Taniguchi, M., Wei, L., Inoue, S., “Extremely environment friendly top-emitting AlGaN-based deep-UV light-emitting diode,” ACS Photonics, 13 (21), 2026, pp. 6333–6338. Doi: 10.1021/acsphotonics.6c00589
Writer’s affiliation: Nationwide Institute of Info and Communications Know-how (NICT), Kobe Metropolis.
License: Open Entry below CC BY-NC-ND 4.0. © 2026 American Chemical Society.
Paper key phrases: aluminum gallium nitride, deep ultraviolet mild emission, mild emitting diode, prime emission machine, mild extraction effectivity, excessive outlet effectivity.
Supply: ACS Photonics; https://doi.org/10.1021/acsphotonics.6c00589 – Read the original paper at ACS Publications
