| In this work, we have utilized the unique properties of III-nitride materials in order to demonstrate high-power ultraviolet light-emitting diodes with peak emission in the wavelength range of 250-340 nm. Most of the work is focused on the optimization of AlGaN epilayers used in the structure of these UV LEDs. There are numerous applications for UV LEDs: High-efficiency low-cost white lighting is one of the major applications that can have an impact on the market in the near future. An UV LED can be used to pump RGB phosphors in order to generate white light. Another important application of UV LEDs, especially at the aforementioned wavelengths, is detection of biochemical agents. Certain agents fluoresce when illuminated by an UV excitation source. The fluorescent light from these agents can then be sensed in order to detect the existence of those particular agents. Another important industrial application is the disinfection of air and water which requires light sources emitting optimally at 265 nm.; Growth of high-quality AlGaN epilayers, suitable for device application, is a very challenging task. Due to the absence of commercially available native substrates, III-nitride epilayers are forced to grow on lattice mismatched sapphire substrates, resulting in the generation of a large number of dislocations. In addition, due to their wide bandgap, doping levels in AlGaN epilayers are usually low, specially with increasing Al mole fraction (more than 35% Al is necessary for emission at such short wavelengths). In addition, large built-in polarization and piezoelectric fields lead to unwanted band bending that reduces the overlap of electron and hole wavefunctions, thereby reducing the rate of radiative recombination. In spite of all these problems, by optimizing the growth conditions and also by optimizing fabrication techniques, we have been able to demonstrate UV LEDs with optical output powers of over 6 mW at a wavelength of 280 nm, over 5 mW at 265 nm, and over 3 mW at 250 nm.; In this dissertation I have tried to explain the various problems associated with the realization of short wavelength UV LEDs and to describe our approach to resolve these issues. |
