Semiconductor lasers with emission wavelengths in the ultraviolet (UV)-B (280-315 nm) and UV-C (100-280 nm) bands are important for a broad range of applications including sensing, disinfection, and non-line-of-sight (NLOS) communications, surface treatment and chemical/biochemical sensing. To date, such deep UV lasers are limited to a few gas lasers and lasers based on frequency conversion using nonlinear crystals, which are bulky and inefficient. In this regard, AlGaN quantum well lasers with high Al content have been intensively studied. Although optically pumped AlGaN quantum well lasers in the UV-B and UV-C bands have been demonstrated, electrically pumped AlGaN quantum well lasers have remained limited in the UV-A band (315-400 nm), with thresholds on the order of tens of kA/cm2. It is envisioned that AlGaN nanowires could be a viable technology towards practical all-semiconductor deep UV lasers through direct current injection.