Improvements of the internal quantum efficiency by reduction of the threading dislocation density and of the light extraction by using UV transparent p-type cladding and contact layers, UV reflecting ohmic contact, and chip encapsulation with optimized shape and refractive index allowed us to obtain the external quantum efficiency of 10.4% at 20 mA CW current with the output power up to 9.3 mW at 278 nm for AlGaN-based deep-ultraviolet light-emitting diodes grown on sapphire substrates.

We report blue-purple pn-junction light-emitting diodes (LEDs) with a-plane GaN–InGaN multiple quantum well active region. The LEDs were grown over r-plane sapphire substrates. Our study has shown the low pump intensity photoluminencence and electroluminescence to be dominated by emission from the band-tail states which then saturates rapidly giving rise to band-edge emission.

The need for efficient, compact and robust solid-state UV optical sources and sensors had stimulated the development of optical devices based on III–nitride material system. Rapid progress in material growth, device fabrication and packaging enabled demonstration of high efficiency visible-blind and solar-blind photodetectors, deep-UV light-emitting diodes with emission from 400 to 250 nm, and UV laser diodes with operation wavelengths ranging from 340 to 350 nm. Applications of these UV optical devices include flame sensing; fluorescence-based biochemical sensing; covert communications; air, water and food purification and disinfection; and biomedical instrumentation. This paper provides a review of recent advances in the development of UV optical devices. Performance of state-of-the-art devices as well as future prospects and challenges are discussed.

We report AlGaN deep ultraviolet light-emitting diodes (LEDs) at 250 and 255nm that have short emission wavelengths. For an unpackaged 200×200μm square geometry LED emitting at 255nm, we measured a peak power of 0.57mW at 1000mA of pulsed pump current. For a similar device emitting at 250nm the peak output power of 0.16mW was measured at 300mA of pulsed pump current. Progress is based on the development of high quality AlGaN cladding layers with an Al content up to 72%, which were grown over AlGaN∕AlN superlattice buffer layers on sapphire substrates. These n-Al0.72Ga0.28N layers were doped with Si up to about 1×1018cm−3 and electron mobilities up to 50cm2∕V∙s were estimated. High resolution x-ray diffraction studies gave a narrow (002) rocking curve with full width at half maximum of only 133arcsec.

We present the analysis of the external quantum efficiency in AlGaN deep ultraviolet (DUV) light-emitting diodes (LEDs) on sapphire substrates and discuss factors affecting the output power of DUV LEDs. Performance of the LED is related to optimization of the device structure design and improvements of the epitaxial material quality.