Nanowire UV LEDs on graphene

One of the most basic necessities for human life is the access to clean air and water. Many places this is achieved by sterilization and purification of less clean resources by ultraviolet (UV) light sources that effectively kill bacteria. As the international community is aiming to become mercury-free and mercury-containing UV lamps will be completely banned from 2020 through the Minamata Convention, there is a need for new, cheap and efficient technology to provide these applications. A promising candidate is the UV light emitting diode (LED). Current UV LED technology, especially in the UVC part of the spectrum, has a low efficiency and high prices due to material-related challenges and the use of expensive materials with complex fabrication. By utilizing novel device designs based on nanostructuring the LED materials in the form of nanowires, we believe we can reduce the material footprint and improve the efficiency. Furthermore, we are using graphene, a one-atom thick sheet of carbon atoms, to decrease the complexity of the fabrication process, as the graphene serves both as the growth substrate and transparent conducting electrode. In the project we developed various UV LED prototype chips based on positioned growth of AlGaN nanowires on graphene. In 2020 we reached a wavelength of 275 nm, which is the optimal wavelength for water disinfection. Furthermore, we developed a 45 mil die by standard processes which was integrated in a hermetically sealed SMD package. In 2021 we focused on further improvement of the power output and lifetime in the preparation for our first product. In the preparation for the market entry of our UVC LED, we have worked through various partnerships and contracts with graphene suppliers, processing partners, packaging partners and distributors to define supply quantities, price agreements and terms of supplier management. We have also implemented a targeted communication plan to the OEM water purification market including business meetings and webinars.

Our revolutionary approach to produce UVC LEDs, based on AlGaN nanowires-on-graphene, has the potential to eliminate the shortcomings of traditional thin-film-based design. The project was focused on solving and optimizing key material challenges, to reach UVC wavelengths and to optimize the efficiency. In the project we focused on both random and positioned AlGaN nanowires and reached the target wavelength of 275 nm. The results will have important benefits for the R&D of nanotechnology-based UVC LEDs but also for enabling devices in other application areas using a similar hybrid platform of semiconductor nanowires with 2D materials. Such devices are expected to enhance the flexibility, performance, energy output and price of semiconductor products, such as solar cells, other LEDs as well as lasers, power- and nano-electronics. Once we demonstrate the superior performance of our unique UVC LEDs, they will play a crucial role in the fast-growing disinfection markets globally.

In the proposed project CrayoNano AS will develop deep UV LEDs based on AlGaN nanowires (NWs) on graphene. The AlGaN NWs will be used as the UV emitting material, whereas graphene will be used both as a substrate for the NW growth and a UV transparent electrode. This may offer a breakthrough in the making of high-efficiency deep UV LEDs and allow disinfection and sterilization treatments on a much larger scale than is possible today. Existing deep UV (UVC) LEDs have a wall plug efficiency (WPE) of only 3-6%. Environmentally unfriendly mercury bulbs are therefore used instead in almost all UV applications. The UV LED market, and in particular deep UV LEDs, is immature with inefficient and very high prices compared to blue GaN LEDs and the potential for technological advancements are huge. This is mainly due to the very high cost of AlN substrate that is needed to achieve close lattice-match with AlGaN, and the lack of transparent electrodes for deep UV light. For the UV LED to be useful for sterilization and disinfection, it needs to emit in the deep UV range of 265 nm to 280 nm where it kills bacteria and other microbes by directly attacking their DNA at its peak absorption. However, a sudden drop in the performance (efficiency and lifetime) of standard thin film UV LEDs at an emission wavelength < 350 nm is of major concern for its use in such applications today. Today, the UVC market is therefore totally dominated by traditional mercury bulbs. This research project will therefore focus on solving and optimizing key material challenges in the active AlGaN nanowire UV emitters in order to reach deep UV wavelengths (<280 nm) and optimize the efficiency beyond state-of-the-art on the market today. This project will form the technical basis to develop and commercialize novel nanomaterials-based deep UV LEDs that could result in cheaper and more compact handheld devices for water and tool disinfection in especially medical applications.