Semiconductor lasers have been used in many fields due to their compactness and high efficiency. In this paper, we report on recently realized UV-B AlGaN-based laser diodes, focusing on the perspective of crystal growth techniques. We also discuss the effect of dislocations in UV AlGaN-based lasers by comparing the threshold power densities of optically pumped lasers and the internal losses measured by using the optically pumped variable stripe length method. As a result, it was found that dislocations in AlGaN lead to non-radiative recombination and increased internal losses, and the realization of high quality AlGaN crystals is very important for the realization of high-performance UV lasers. After describing the high current density operation using polarization doping, the characteristics of laser diodes based on these techniques are introduced.
