Sensor Electronic Technology, Inc (SETi) of Columbia, South Carolina USA, announced record efficiencies of UV LEDs operating in the germicidal UV-C range of 11% external quantum efficiency (EQE) with a corresponding wall-plug efficiency (WPE) of 8%. This was achieved under the DARPA Compact Mid-Ultraviolet Technology (CMUVT) program in collaboration with Army Research Laboratories (ARL).
The company notes that this is more than 5X improvement in performance. The company attributes this improvement primarily to improved light extraction from encapsulated LED chips with a novel transparent p-region and a reflective contact and reductions in defect density in the LED structure on a sapphire substrate.
SETi points out that traditionally, UV LEDs are manufactured with GaN p-layers, due to the difficulties of p-doping AlGaN materials. However, GaN absorbs wavelengths shorter than 365nm, thereby reducing the extraction efficiency of short wavelength UV LEDs. SETi says it has developed a new p- type region using doped AlGaN, which is transparent in the UVC range. The company says that this along with a transparent p-contact significantly increases extraction efficiencies.
SETi reduced dislocation densities in quantum well structures with further development of its MEMOCVD® growth process on sapphire. SETi demonstrated threading dislocation densities (TDD) of less than 2x108 (measured by TEM) which the company claims led to internal quantum efficiency (IQE) of 60%. The encapsulated LEDs measuring 350um x 350um, emit at 278nm. They emitted 9.8mW at 20mA (the highest ever reported for Short wavelength UV) and 30mW at 100mA.
Source:
