The biggest task in developing deep UV-LEDs was, how to achieve high-power light. Yusuke Matsukura, who is in charge of developing chips in the UV-LED Business, stated that, "Since the deep UV-LEDs were different from regular LEDs, it was necessary to make the structure of a chip that matched the deep UV-LEDs." Normally, LED light is emitted by making a PN junction where the n-type layer and p-type layer are joined and the current flows through there. However, in the case of deep UV-LEDs, the chip is manufactured mainly using AlGaN material and growing the crystals.

"Because making the p type AlGaN* is very difficult, GaN, which has been also used in blue LEDs, is used for the p-type layer. In the case of blue LEDs, since the emitted light is not absorbed even when a GaN is used for the p-type layer, the light can be effectively removed. However, in the case of deep UV-LEDs, since generated light is absorbed in the GaN layer if the GaN is used for the p-type layer, it has been necessary to change the structures of both the chip and wafer to make high-powered LEDs." (Matsukura)

Although there was a case where the "wafer glowed tremendously" (Matsukura) in the experiment, the wafer did not glow even afterwards even when created with a method, and then trial production and analysis was repeated for about half year. "Although several months passed before we identified the cause, we happened to take notice of the idea that the cause might be an influence of a certain material that our company newly introduced, and we tried to create wafers by changing the conditions in various ways." (Matsukura) As a result, the glowing wafer was reproduced. Thus, development of the High-powered deep UV-LEDs took a step forward.

* Making the p type AlGaN denotes adding an impurity that operates as the p type to the AlGaN, and creates the p-type semiconductor.

The package for deep UV-LEDs with a size of 3.5 mm received very high evaluations from many customers. Around that time, a certain client consulted with us as to whether deep UV-LEDs would be applicable to water purifying plants, instead of mercury lamps. The Module Development Group, including Hiroki Kiuchi, responded to this consultation. It was said that the mercury lamps have a risk of adversely affecting the human body, etc., and the international treaty, called the "Minamata Convention on Mercury" was concluded in 2013. "Because 'Mercury free' fields were targeted, naturally applications for water disinfection were included in the plan. However, in the case of large quantities of water such as water purifying plants, the method for enabling certain and effective water disinfection must be considered." (Kiuchi)

Although the water disinfection module of "2 L/min," applicable to drinking water at home, etc. was already at the end of the development stage, the ability to process even larger amounts of water, namely 50 to 100 L/min, is required in the case of water purifying plants. For that purpose, Kiuchi and other members made an array of multiple deep UV-LEDs to enhance disinfection ability and improve the light's use efficiency via the structure of the package. As a result, disinfection ability for 120 L/min or more was confirmed.

"There are still so many items to be considered, such as what we will do if it fails, what to do during repairs, and so on. We are aiming for a solution so that customers can use the deep UV-LEDs with a sense of security for a long period." (Kiuchi)