Optimization of underlying layer and the device structure for group‐III‐nitride‐based UV emitters on sapphire

Abstract

Epitaxial lateral overgrowth (ELO) was applied for the growth of AlGaN on a sapphire substrate by metalorganic vapor phase epitaxy. Among several processes, the ELO of AlGaN on grooved AlGaN showed the best surface morphology and the lowest dark‐spot density of 1×108 cm–2 as measured using cathodoluminescence. The light output power of a UV LED fabricated on ELO‐Al0.25Ga0.75N on grooved Al0.25Ga0.75N was the strongest among several UV LEDs fabricated by different processes. The effect of the Al composition in the electron‐blocking (EB) layer on the performance of UV LEDs was investigated. The UV LED with a low‐Al‐content EB layer showed high output power under a low‐injection condition, while the output power of a UV LED with a high‐Al‐content EB layer did not saturate even under a high‐injection condition. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)