Ultraviolet light-emitting diodes (UV-LEDs) have started replacing UV lamps. The power per LED of high-power LED products has reached 12 W (14 A), which is 100 times the values observed ten years ago. In addition, the cost of these high-power LEDs has been decreasing. In this study, we attempt to understand the technologies and potential of UV-LEDs.

Design and fabrication of monolithic blue LED series arrays that can be operated under high ac voltage are described. Several LEDs, such as 3, 7, and 20, are connected in series and in parallel to meet ac operation. The chip size of a single device is 150 μm × 120 μm and the total size is 1.1 mm × 1 mm for a 40 (20 + 20) LED array. Deep dry etching was performed as device isolation. Two‐layer interconnection and air bridge are utilized to connect the devices in an array. The monolithic series array exhibit the expected operation function under dc and ac bias. The output power and forward voltage are almost proportional to LED numbers connected in series. On‐wafer measurement shows that the output power is 40 mW for 40 (20 + 20) LED array under ac 72 V.

With the widespread of the novel coronavirus (SARS-CoV-2), the inactivation of bacteria and viruses using ultraviolet (UV) light has been reevaluated. However, there are many applications where the safety to the human body itself and inactivation effect itself are questioned, and there is a movement to review the UV-C guidelines (Global Lighting Association, Position Statement on Germicidal UV-C Irradiation UV-C SAFETY GUIDELINES, 2020). Since the Minamata Convention on Mercurybans the production of mercury in principle, deep-ultraviolet light-emitting diodes (UVC-LEDs) are now being used in place of mercury lamps. In this paper, we will discuss effective irradiation methods for the inactivation of pathogens on solid surfaces, the inactivation of pathogens in water, and the inactivation of viruses in aerosols using UVC-LED.

Abstract— Progress in the development of blue light‐emitting diodes and yellow phosphor has led to the realization of solid‐state lighting. The development was followed by improvement in the luminous efficacy of ultraviolet light‐emitting diodes (UV‐LEDs). By using near‐UV‐LEDs (n‐UV‐LEDs) excited light for red, green, and blue (RGB) phosphors, a new type of solid‐state lighting was realized. An innovative method for increasing the efficiency of LEDs by using a silicon nitride layer as the active layer and piling them up to a nano‐sized level with nano‐sized holes has been developed.

Micro light emitting diode (μLED) displays have been in development since 2017, aimed for application in 2020. However, when using three-color, i.e., red, blue, and green LEDs, or blue LEDs that excite red and green phosphors, many challenges arise in mass production, cost, and quality. Our group has devised an ultraviolet (UV)-excited red, green, and blue (RGB) display that excites red, green, and blue phosphors using UV-LEDs. This paper studies how the composition and crystal defects of a light-emitting layer affect the luminous efficiency of a UV μLED chip from the perspective of internal quantum efficiency (IQE). It was confirmed that the luminous efficiency improves by making the LED chips in the near ultraviolet range μ-size. The UV μLED chip emitting at 385 nm exhibited a more linear output than a 400-nm purple μLED chip.