Quasi-pseudomorphic AlGaN based deep ultraviolet LEDs over sapphire substrates

III-Nitride sub-290 nm deep ultraviolet (DUV) light emitting diodes (LEDs) have the potential to replace the existing mercury lamps used in air/water purification, Bio-agent detection, Phototherapy and biomedical instruments sterilization applications. Most of the research activity 1–2 has been so far focused on improving the DUV LED's external quantum efficiency by increasing the carrier injection, radiative recombination and light extraction efficiency. Almost all nitride based deep UV LEDs are grown on sapphire substrates, mainly due to their transparency to UV light, low cost and availability. Nearly all the devices utilize a relaxed epilayer structure with thick n+-AlGaN current spread layers and strain relieving AlGaN-AlGaN superlattices inserted between the AlN buffer layers and the quantum-well active region.