The 70th Japan Society of Applied Physics Spring Meeting 2023
Highlighted Presentations Press Release
April 18, 2023

Development of 230-nm Wavelength Range UV-LEDs on Sputtered and Annealed AlN

Ultraviolet LEDs Enable Future “Sterilization andDisinfection Devices”
Organization for Research Initiative and Promotion, Mie University1 , Graduate School of Regional Innovation Studies,
Mie Univ.2 , Graduate School of Engineering, Osaka Univ.3 , Research Center for Ultra-High Voltage ElectronMicroscopy, Osaka Univ. 4 , Graduate School of Engineering, Mie Univ.5 , Stanley Electric Co.6
Kenjiro Uesugi 1,2 , Shuhei Ichikawa 3,4 , Shiyu Xiao5 , Kanako Shojiki3,5 , Takao Nakamura5 , Masahiko Tsuchiya6 ,Kazunobu Kojima3 , Hideto Miyake5
E-mail: k.uesugi@opri.mie-u.ac.jp

Summary• Sputter-annealed aluminum nitride (AlN) enables low-cost, high-performance UV-LEDs
with wavelengths from 260 nm to 280 nm that inactivate bacteria and viruses.
• UV-LEDs with wavelengths of 220–230 nm that do not cause damage to the human body
have been realized.
• This fundamental technology is capable of becoming a future infrastructure for thesterilization and disinfection of society.
A research group led by Kenjiro Uesugi of the Organization for Research Initiative and Promotion at Mie University havedeveloped a UV-LED that generates far-UV light capable of inactivating bacteria and viruses. Employing a original
method called “face-to-face annealed and sputter-deposited AlN (FFA Sp-AlN),” the group has realized a UV-LED with awavelength of 260 nm to 280 nm that can inactivate bacteria and other viruses. In addition, a wavelength of 220–230 nm,
which does not damage the human body, has been realized. This technology which operates on a power supply
equivalent to that utilized in households is low-cost, enables non-contact sterilization and disinfection, and is truly thesterilization and disinfection device of the future.

DetailCurrent Status and Issues of Glowing Sterilization and Disinfection
Since the pandemic of the COVID-19, a global crisis in public health, disinfection and sterilization
have become a part of society's infrastructure worldwide. However, the existing disinfection
methods rely significantly on liquid disinfectants. Liquid disinfectants have the disadvantages ofbeing very large in volume, expensive to clean because disinfectants adhere to the area aroundthe sprayer when used on the human body, and difficult to operate and manage from thestandpoint of replacement costs.
A research group led by Kenjiro Uesugi of the Organization for Research Initiative and Promotion
at Mie University has developed a UV-LED that generates far-UV light capable of inactivating
bacteria and viruses. When ultraviolet light strikes bacterial DNA, a few DNA bonds are broken andthe bacteria are unable to multiply. This is due to bacterial inactivation by ultraviolet light.
Mercury lamps have been utilized as UV light sources to inactivate bacteria and viruses. However,
mercury lamps can only emit a fixed wavelength of 254 nm and the devices themselves are large(several centimeters to several tens of centimeters). In addition, they have the disadvantages ofsolely operating at high voltages, high costs, and high environmental impact.
LEDs that generate ultraviolet light with wavelengths in the 260–280 nm range have already beencommercialized. However, commercially available UV-LEDs in this wavelength range have low
output power and high device prices, which are barriers to their social implementation. Therefore,
we developed a highly functional and inexpensive UV LED utilizing our proprietary thin-film crystal
growth technology, stated Uesugi.
High temperature annealing at 1700 °C eliminates crystal defects
Uesugi and his research group focused on “threading dislocations,” defects that exist insemiconductor crystals. Nitride semiconductors which make up LEDs have high output power andefficiency when there are few threading dislocations and the atoms are arranged neatly. Therefore,
the fewer the number of threading dislocations, the more efficient the conversion of power into
ultraviolet light.
In semiconductor manufacturing, thin films of crystals for n-type, light-emitting, and p-type layers
are grown on a crystal substrate (wafer) using “thin-film crystal growth technology,” andsemiconductor chips are fabricated by cutting the substrate. In this process, an aluminum nitride(AlN) freestanding substrate with fewer defects is known to reduce threading dislocations, which
are defects in semiconductors, and improve the performance. Utilizing freestanding aluminumnitride (AlN) substrates can achieve a high performance. However, a single 2-inch substrate alone
costs several thousand dollars; thus, cost reduction cannot be achieved.
A way to reduce costs is to utilize inexpensive industrial sapphire substrates. The price of thesubstrate can be reduced to approximately one-hundredth that of a freestanding aluminum nitride(AlN) substrate. However, when sapphire substrates are used, aluminum nitride (AlN) templates
have to be stacked on top of the sapphire substrate. The disadvantage of stacking materials withdifferent crystal structures is that an extremely significant number of crystal defects are generated,which reduces the performance of the LEDs and makes it impossible to achieve high functionality.

The method proposed by Uesugi and his research group is “face-to-face annealed and sputterdeposited AlN (FFA Sp-AlN),” which offers both low cost and high performance. The researchgroup employed the sputtering method as the deposition technology. Sputtering is a film deposition
technology employed in the fabrication of large-area displays. However, semiconductor crystal
fabricated by sputtering results in far more crystal defects than those prepared by common
metalorganic vapor phase epitaxy method. We then annealed (heat-treated) the films at a hightemperature of 1,700 °C after deposition. Consequently, the crystal defects that occurred during
deposition by the sputtering method were eliminated, and a high-performance thin film wascreated."
Normally, exposure to temperatures as high as 1,700 °C would cause thermal decomposition anddamage to the sapphire substrate and thin film of aluminum nitride (AlN); however, the researchgroup has established a method that can eliminate only crystal defects without causing thermal
decomposition using a unique “face-to-face” arrangement of two substrates facing each other. FFA
Sp-AlN can reduce crystal defects even in thin films that are far thinner than those produced by thegeneral metalorganic vapor phase epitaxy method. The advantage of using FFA Sp-AlN is that thinfilms with fewer crystal defects can be fabricated (Figure 1).
Toward the Disinfection Devices of the Future
The UV LEDs (Figure 2) realized by the research group using FFA Sp-AlN can be operated with apower supply equivalent to that utilized in households. They are hygienic because they enablenon-contact sterilization and disinfection, far less expensive than conventional mercury lamps, andenvironmentally friendly.
Because of these characteristics, their application areas are wide. For example, irradiation of foodcan delay spoilage. This approach can provide a solution to the issue of food loss in several
developed countries. It can also be employed to build water purification systems in developing
countries that face challenges in procuring clean drinking water. A research group is currently
focusing on UV LEDs to achieve a wavelength of 220–230 nm that does not cause damage to thehuman body. The advantage of being harmless even when directly irradiated on humans, furtherexpands the range of applications. It is truly the disinfection and sterilization device of the future.
Compared with conventional aluminum nitride (AlN) freestanding substrates, sapphire substrates
and FFA Sp-AlN can reduce costs by approximately one-tenth. In the future, we will expand ourtechnologies to manufacturers that replace mercury lamps with UV LEDs and develop high-valueadded sterilization and disinfection equipment.

Annotation※ Metalorganic vapor phase epitaxy (MOVPE): A commonly employed crystal growth method for fabricating compoundsemiconductors. It utilizes mixed gases containing organometallic materials as raw materials, and is a key technology
for the mass production of optical devices.

Figures

Figure 1 Comparison between existing UV-LEDs and this study

Figure 2 Prototype UV-LED