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 by Staff Writers Pohang, South Korea (SPX) Jan 20, 2022
A Korean research team has developed a deep-ultraviolet (DUV) LED with an entirely new material. The DUV LED refers to a semiconductor light source designed to emit ultraviolet (UV) light with a short wavelength of 200 to 280 nanometers. Irradiating this LED on viruses or bacteria destroys harmful pathogens while minimizing harm to the human body. A POSTECH research team led by Professor Jonghwan Kim and Ph.D. candidates Su-Beom Song and Sangho Yoon (Department of Materials Science and Engineering) has produced DUV LED for the first time using hexagonal boron nitride (hBN). Unlike visible light, UV light can destroy or alter the form of a material. Among UV lights, the near-UV light has high penetration depth and can cause diseases when the skin is exposed to it. However, DUV light has extremely low skin penetrability and is anticipated to be safely used. For this reason, research to develop DUV LEDs has been active, mainly using aluminum gallium nitride (AlxGa1-xN). However, this material has a fundamental limitation in that its electroluminescence rapidly deteriorates as the wavelength becomes shorter and fabricating LEDs that can be used in the DUV frequencies remains a challenge. Hexagonal boron nitride (hBN) used by Professor Jonghwan Kim's research team is a van der Waals (vdW) layered material like graphite. It is often called the 'white graphene' because its monolayer structure is similar to graphene and is transparent. Unlike AlxGa1-xN, it emits luminescence at DUV frequencies and therefore considered an effective new material for developing DUV LEDs. However, it has been difficult to inject electrons and holes due to its large bandgap, rendering it difficult to make into an LED. To this, the researchers focused on injecting electrons and holes to the hBN band edges by applying a strong voltage to the hBN nanofilm inducing the tunneling mechanism. With this, the researchers successfully fabricated an LED device based on a van der Waals heterostructure stacked with graphene, hBN, and graphene. Subsequent DUV micro-spectroscopy confirmed that the newly fabricated device emits strong UV light. "The development of a new high-efficiency LED material in a new frequency can be the starting point for pioneering groundbreaking optical device applications that have never been seen before," remarked Professor Jonghwan Kim who led the study. "It is significant that this study presented the first demonstration of a deep-ultraviolet LED based on hBN." He added, "Compared to the conventional AlxGa1-xN material, the new material has significantly higher efficiency of luminescence and enables miniaturization. It is anticipated to be highly applicable in viral and bacterial sterilization systems, semiconductor device manufacturing processes, and short-range wireless communication in the future." Recently published in the world-renown journal Nature Communications, this research was conducted with the support from the Senior Researcher Program of the National Research Foundation of Korea and the Institute for Basic Science.
Research Report: "Deep-ultraviolet electroluminescence and photocurrent generation in graphene/hBN/graphene heterostructures"
Organic light emitting diodes operated by 1.5 V battery Tokyo, Japan (SPX) Jan 07, 2022 Various properties of organic light-emitting diodes (OLEDs) have been optimized, including current to photon conversion efficiency. An external quantum efficiency exceeding 20%, with internal quantum efficiency of 100%, has been achieved owing to the development of thermally activated delayed fluorescent and phosphorescent materials that manage the spin of excited states. However, the operating voltage of common types of OLEDs is very high; that of an OLED emitting approximately 600-nm light at a ... read more
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