Researchers in Korea and USA have developed sidewall emission-enhanced (SEE) deep ultraviolet (DUV) light-emitting diodes (LEDs) to improve light extraction efficiency
DUV LEDs with wavelengths less than 300nm become very inefficient due to an increasing tendency for the photons to be emitted in the plane of the device. The problem arises from the band structure of high-aluminium-content aluminium gallium nitride (AlGaN) used for short-wavelength LEDs.
In such materials the dominant electron transition is from the conduction band to a crystal-field split-off hole state in the valence band. This transition emits photons with transverse magnetic polarization that propagates perpendicular to the c-direction of the crystal structure.
There has been some progress in improving DUV LEDs, with an external quantum efficiency (EQE) of 10% reported for 278nm wavelengths. However, commercial devices languish around 5% EQE. These values fall far short of the EQE of more than 80% for visible LEDs based on gallium indium nitride (GaInN).
If these problems can be overcome, applications beckon such as air/water/food purification/sterilization, polymer curing, semiconductor photolithography, and high-density optical recording. LEDs would then be able to replace bulky, fragile, poisonous mercury lamps or more complex, expensive systems.
The researchers from Pohang University of Science and Technology and Samsung Electronics in Korea and Rensselaer Polytechnic Institute in the USA have developed the SEE structure to enable better extraction of the in-plane transverse-magnetic radiation.
