High-power extraction of 340- to 350-nm UV LEDs

The potential of high power extraction from AlGaN-based ultraviolet light emitting diodes (UV-LEDs) is described. Improvements of UV-LEDs are shortly introduced from the viewpoints of nitride epitaxial growth, heterostructure optical characteristics based on the internal polarization field, and p-n junction design. The UV light extraction enhancement by utilizing the GaN-free transparent UV-LED structure and highly efficient UV-LEDs fabricated by introducing a high-quality AlN template on sapphire substrate are described. The maximum output powers are 8.6 mW and 5.5 mW at an injection current of less than 150 mA, at the emission wavelength of 350 nm and 340 nm, respectively. The highest external quantum efficiencies are 2.2 and 1.7%, respectively. The application to white lighting and the potential of the high-flux UV-extraction utilizing bulk AlN substrate are also investigated.