Development of high efficiency 255–355 nm AlGaN‐based light‐emitting diodes

We report on the fabrication and characterization of high efficiency ultraviolet (UV) light emitting diodes (LEDs) with emission wavelength ranging from 255 to 355 nm. Epi‐layers of UV LEDs were grown on AlGaN templates with sapphire substrates. Flip‐chip configuration without removing sapphire is used for characterization of the UV LEDs. External quantum efficiencies (EQEs) over 3% were obtained for all the investigated wavelengths with maximum value reaching 5.1% for 280 nm LED. Under RT DC operation at a current of 500 mA, output powers of 38, 77, and 64 mW were measured for 257, 280, and 354 nm, respectively. By using enhanced light extraction technologies, such as, moth‐eye structure on the back side of the sapphire substrate, we expect to improve these values by up to 50%.