Germicidal ultraviolet LEDs: a review of applications and semiconductor technologies

Ultraviolet LEDs are one of the most promising technologies for preventing future pandemics, improving health outcomes, and disinfecting water sources. Currently available UV LEDs emitting in the conventional germicidal wavelength range (254 nm – 285 nm) have efficiencies below 5% and cost about 100 times more (per watt) than mercury vapor lamps. On the other hand, germicidal UV LEDs provide many advantages over vapor lamps including instant-on and dimmable functionality, wavelength tunability, miniaturization, and durability, and are already in widespread use for certain applications. It is expected that III-nitride based UV LEDs will soon have similar cost and efficiency to white LEDs and will become the dominant germicidal light source within this decade. Unlike vapor discharge lamps, LEDs have theoretical efficiency limits approaching 100%; the challenges to improving UV LED efficiency are not fundamental, but technological. Improvements in material quality, chemical purity, electrical conductivity, optical transparency, and fabrication technologies are needed. In this review, we outline the major challenges in each of these areas and summarize the recent advances that have enabled rapid improvements in UV LED efficiency within the past five years. We discuss the physical principles underlying the mechanisms of improved efficiency, and comment on likely future trends in UV LED design and commercialization.