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SETi Breaks Barriers With UV-C LED Efficiencies Of Over 10%

Bringing consumer disinfection markets within reach, SETi has developed a completely new p-type region using doped transparent aluminium gallium nitride. This, together with a transparent p-contact, significantly increases extraction efficiencies

Sensor Electronic Technology, Inc (SETi) has achieved, what it says, are record efficiencies of ultraviolet light (UV) LEDs operating in the germicidal UV-C range. UV Germicidal LED lamps with the power to disinfect water, surfaces and air Literature says that the UV-C range peaks at around 254nm although the latest LEDs developed by SETi have been designed to emit at 278nm. The firm's latest devices have an external quantum efficiency of 11% with a corresponding wall-plug efficiency of 8%.  SETi says this is an "industry beating result". It was achieved under the DARPA Compact Mid-Ultraviolet Technology (CMUVT) program and performed in collaboration with Army Research Laboratories (ARL). This latest development represents more than a five times improvement in performance. Traditionally, UV LEDs have been manufactured with GaN p-layers, due to the difficulties of p-doping AlGaN materials. However, GaN absorbs wavelengths shorter than 365nm, reducing the extraction efficiency of UV LEDs operating at short wavelengths. SETi has now developed a completely new p-type region using doped AlGaN, which is transparent, even in the UVC range. This coupled with a transparent p-contact significantly increases extraction efficiencies. The firm has also enhanced its proprietary MEMOCVD growth process to reduce dislocation densities in the quantum well structure of UV LEDs grown on sapphire substrates. The company has demonstrated threading dislocation densities of less than 2 x 108, as measured by TEM. This improvement leads to a high internal quantum efficiency of 60%.  “This milestone is a very exciting development of UV LEDs, and represents a major step forward in reaching efficiencies of incumbent technologies, such as medium pressure mercury vapour lamps, which typically operate at efficiencies of 15% or less," notes Remis Gaska, President and CEO of SETi. The 350µm x 350µm encapsulated LEDs were designed for emission at 278nm and measured independently at ARL. SETi says the emission of 9.8mW at 20mA is the highest value ever reported for an LED shorter than 365nm at this forward current, and 30mW at 100mA. Details of the research will be presented at CLEO 2012 meeting, San Jose, California. SETi has previously reported LED based water treatment systems that disinfect with over 4 log reduction drinking water flowing at 0.5 litres per minute with less than 35mW of optical power at 275nm. The results from this development put UV LED disinfection systems within the reach of consumer markets for applications such as point of use water purification.

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