| This research addressed the development of AlGaN-based deep ultraviolet light emitting diodes (UV-LEDs). Deep UV-LEDs are crucial for a number of applications such as water purification, free space non-line-of-sight communications, and fluorescence identification of biological agents. Reports in the existing literature indicate that such devices are highly inefficient, a result that can be accounted for by low internal quantum efficiency (IQE), low carrier injection efficiency (IE), low light extraction efficiency (EE), or a combination of all three factors. The focus of my research was to develop such devices on inexpensive sapphire substrates and address materials issues such as strain management to prevent nucleation and propagation of cracks as well as device issues such as the IQE and the IE.;To improve the IQE, I developed methods of growth to introduce band structure potential fluctuations in the AlGaN quantum well (QW) layers. Such potential fluctuations are the result of either lateral compositional inhomogeneities of the AlGaN alloy or of partial alloy ordering, where the ordered domains have a smaller energy gap than the random domains. The injected electron-hole pairs in the QWs are localized at the minima of such potential fluctuations and form excitons, and thus are prevented from migrating to and recombining non-radiatively at dislocations.;The novel feature of the AlGaN QWs provides additional design flexibility in the n-AlGaN cladding layer of the device. The emission is red shifted from the wavelength corresponding to homogeneous alloy and this allows employment of n-AlGaN cladding layer with reduced AlN mole fraction. Such device design includes also efficient carrier injection layers at the n- and p-sides of the device, which lead to significant improvement in the IE.;Deep UV-LED structures emitting from 320 nm to 270 nm were grown by plasma-assisted MBE and fabricated into devices. A flip-chip bonded UV-LED emitting at 273 nm with CW output power of 0.35 mW at 20 mA and AC output power of 1.3 mW at 100 mA were obtained, and its maximum CW external quantum efficiency is 0.4%. The device performance would improve further by removing the substrate and texturing the n-layer surface to increase the EE. |
