ICULTA 2023: Expanding horizons for deep-UV LEDs
Tremendous progress is underway with the deep-UV LED, in terms of its
use in healthcare and it gains in output power, efficiency and lifetime,
in both the UVC and far UVC.
BY MICHAEL KNEISSL FROM TU BERLIN AND THE FERDINAND-BRAUN-INSTITUT
Devices that attract a great deal of attention tend to have breakthroughs on many fronts. As well as a hike in performance, they often undergo improvements in reliability, along with increasing interest from more applications, opened up by superior characteristics. That’s certainly the case for the deep-UV LED. Its increasing power and lifetime in both the UVC and the far UVC is attracting interest for fighting hospital germs and airborne viruses.
Reports of progress in all these areas lay at the heart of the third International Conference on UV Light Emitting Technologies and Applications, known as also ICULTA 2023. Held in Berlin, Germany, from 23-26 April 2023, this year’s meeting, which attracted more than 220 attendees from 27 countries, was organised by the recently established Advanced UV for Life e.V. association, together with Ferdinand-Braun-Institut (FBH), Berlin, and in collaboration with the International UV Association (IUVA).
Building better devices
Two solid-state lighting heavyweights helping to drive progress in the UVC are ams Osram and Nichia. At ICULTA 2023 representatives from both these chipmakers unveiled their latest developments in UVC-LED technologies, showcasing peak powers in the disinfection band between 260 nm and 280 nm.
Speaking on behalf of ams Osram were Project Manager Marc Hoffmann and Director of Product Management Christian Leirer. As well as outlining the company’s advances, this duo delivered an excellent overview on the latest advances in UVC-LEDs, as well as their use in industrial and consumer applications. The application space is now moving from consumer to industrial applications, influencing the requirements for UVC-LEDs. To support this trend, ams Osram is improving the performance of its UVC LEDs. Current products are delivering output powers of up to 100 mW when driven at 250 mA, and have a lifetime of 10,000 hours, judged in terms of L70, which is the time it takes for the output power to fall to 70 percent of its initial value. According to the speakers, the third generation of devices from ams Osram are producing up to 200 mW at a wall-plug efficiency (WPE) of 10 percent.
The company has set itself a very ambitious goal, targeting a WPE of 20 percent by 2026, a L70 lifetime of 40,000 hours, and a pricing level that’s just ten times above that of the current cost of the mercury lamp. Such a level of improvement would be revolutionary, ensuring that the cost of a UVC-LED based system is lower than that of a conventional mercury-lamp based system. This rival to the incumbent would also deliver energy savings, alongside enhanced product safety and reliability, thanks to the combination of UVC-LED and UV sensors. Note that this forecast of progress lies within the range that I gave in my presentation (see Figure 1).
Figure 1. Wall-plug efficiencies for production level UVC-LEDs and engineering prototypes in the 250 nm - 280 nm and 225 nm – 235 nm wavelength bands. Credit: Michael Kneissl/TU Berlin
Representing Nichia Europe, Managing Director Ulf Meiners offered an interesting comparison between the chronology of WPE increases for the blue and the UVC-LED, noting that both technological developments appear to be on a similar fast-paced trajectory. Meiners didn’t present an extended outlook, but forecast that the WPE of Nichia’s devices will hit 7.5 percent in 2024, with output power at 280 nm reaching 150 mW.
While many make a direct comparison between UVC-LEDs and mercury lamps using individual performance parameters, Meiners argued that this is not very meaningful. He emphasised the importance of studying concrete use cases that account for the specific properties of UVC-LEDs. For example, it is important to be aware of completely new, more efficient system designs that cannot be realised with conventional UV sources. Merits of deep-UV LEDs that can increase the light utilisation efficiency of the system include point source emission, which enables a tailoring of the source to fit the application, and the opportunity to trim energy consumption – UVC-LEDs are easily dimmable, and can be turned on-and-off rapidly, allowing activation only when it’s needed and at the required power level. This point of view was reinforced by Alexander Wilm, Senior Key Expert Applications at ams Osram, who described several use case scenarios in which UV-C LEDs are already outperforming conventional UV-C lamps despite their lower WPE.
An interesting difference between the two heavyweights is the peak wavelength of their UVC LEDs. Nichia is sticking with its 280 nm LED technology platform, reasoning that the reliability of the UVC-LED is higher at the slightly longer wavelength, while ams Osram is focusing on LEDs centred near the germicidal efficiency peak that’s around 265 nm.
Competition for the production of class-leading devices is coming from a handful of other suppliers, including Crystal IS, a subsidiary of Asahi Kasai. Delegates at ICULTA were given an update on the capability of these devices by Rajul Randive, Director, Applications Engineering, Crystal IS. Randive revealed record performance levels for the company’s 265 nm LEDs, with single-chip output power now as high as 160 mW at 500 mA and maximum WPE reaching 6.5 percent. Unlike most UVC-LED products, those made by Crystal IS are grown on internally produced, low-defect-density bulk AlN substrates. Threading dislocation densities in bulk AlN are many orders of magnitude lower than those found in the heterostructures of UVC-LEDs grown on sapphire. The company attributes the far lower level of threading dislocations to superior device lifetimes. The L70 lifetimes of Crystal IS devices are already reaching 25,000 hours at a drive current of 350 mA.