We demonstrated AlGaN-based multi-quantum-well (MQW) deep-ultraviolet (UV) light-emitting diodes (LEDs) with wavelengths in the range of 222-351 nm, fabricated on low threading dislocation density (TDD) AlN template on sapphire. High internal quantum efficiency (IQE) of 50-80% was observed from AlGaN or quaternary InAlGaN MQWs by fabricating them on low TDD AlN templates. Also, an electron injection efficiency (EIE) was markedly improved by using multi-quantum barrier (MQB). Over 20 mW cw output power was obtained for 256-275 nm LEDs, which will be useful for sterilization applications. The maximum external quantum efficiencies (EQEs) were 1.8 and 2.75% for 247 and 270 nm AlGaN-LEDs, respectively.© (2010) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.