Nitride-Based UV Lasers

The ultraviolet (UV) laser diode (LD) is attracting much attention for various novel applications such as in medical engineering, sterilization and high density optical storage. Group III nitrides are one of the most promising candidates to realize UV LD. The external quantum efficiency of group-Ill nitride-based light-emitting diodes (LEDs) with emission wavelength shorter than 360 nm is still far inferior to that of nitride-based visible-short-wavelength LEDs. Simulation results show that there is no theoretical barrier which hiders the realization of short wavelength UV LDs (Chow, 2005). At the moment, however, the shortest emission wavelength of nitride-based LD is limited to 343nm on SiC (Edmond, 2004) and 350.9 nm on a sapphire substrate (Iida, 2004). In order to overcome the barrier for emission wavelength and to realize much shorter wavelength UV LDs, in addition to the control of conductivity for both n-type and p-type layers, the growth of low-dislocation-density high-Al-content AlGaN with low internal loss is essential.