376 nm High-Power UV-A Laser Diodes With GaN Waveguide

Early studies suggest that absorption coefficient of GaN exceeds 100 cm−1 at wavelengths below 380 nm, indicating GaN might not be suitable as a waveguide (WG) material for laser diodes (LDs) in this range. However, in those studies, material defects (rather than GaN band edge absorption) could contribute significantly to the measured absorption loss. In this work, III-Nitride LDs emitting at 376 nm using unintentionally doped GaN WG was demonstrated for high-power operation. Devices with a cavity length of $750 \; \mu $ m and a ridge width of $10 \; \mu $ m exhibited a threshold current of 625 mA and a slope efficiency of 1.13 W/A under pulsed conditions. The highest output power of 3.4 W was obtained at an injection current of 3.5 A. These promising results suggest that GaN band edge absorption may not be as significant at 376 nm or even shorter wavelengths, allowing more flexibility in epitaxial design.