Ultraviolet Light-Emitting Diodes: Challenges and Countermeasures
The ultraviolet (UV) light is an electromagnetic wave with a wavelength from 400 to 100 nm. UV spectral region is divided into three sub-regions, based on a convention established during the Second International Congress on Light in 1932. Semiconductor-based light-emitting diodes (LEDs) have lots of economic and technical advantages such as high efficiency, small form factor, low voltage operation, and compatibility with modern microelectronic technologies. Epitaxial growth of a high-quality material is the most important issue for developing efficient optoelectronic devices because defects such as cracks, dislocations, and unintentionally incorporated impurities in materials can act as an energy-loss path by generating defect states inside the band gap or nonradiative recombination centers. Since LED is an optoelectronic device based on p–n junction, which converts electrical power to optical power, both electrical and optical properties are important factors determining the overall performance.