"AlGaN-based light-emitting devices are promising ultraviolet light sources to replace the existing UV gas lasers and UV lamps containing toxic substances (mercury). However, the performance of AlGaN-based UV emitters are limited, and in particular high-power UV laser diodes (emitting below 330nm) have not yet been reported. Moreover, the threshold operating voltages of reported UV laser diodes (>330nm) are quite high, surpassing 25V in lasing mode with high series resistance due to poor hole injection efficiency."
"These limitations in device performance are attributed to several factors such as the presence of a high density of defects (dislocations) and inefficient p-type doping of the Al-rich AlGaN layers, and the lack of efficient thermal dissipation channels for existing device schemes. A new device scheme is therefore urgently needed."