350-nm band edge-emitting laser diodes enabled by low-dislocation-density AlGaN templates
Realization of efficient laser diodes with ultra-violet (UV) emission from ~260-360 nm would enable many applications including fluorescence-based biological agent detection, sterilization, and portable water purification. While InGaN-based laser diodes are well developed down to ~370 nm, achieving shorter UV wavelengths requires higher Al-content AlGaN alloys with increasing challenges in achieving p-type doping, strain-management, and low threading-dislocation-density (TDD) AlGaN templates. Given these challenges, few groups have reported AlGaN-based edge-emitting laser diodes (LDs) with emission <; 355 nm.[1, 2] Most recently, random lasing via Anderson localization in AlGaN nanowire structures has demonstrated a novel approach to realizing deep-UV laser diodes.[3].
Entirely Crack-Free Ultraviolet GaN/AlGaN Laser Diodes Grown on 2-in. Sapphire Substrate
We have succeeded in fabricating ultraviolet (UV) GaN/AlGaN laser diodes without any crack generation on a whole 2-in. sapphire substrate using a hetero-facet-controlled epitaxial lateral overgrowth (hetero-FACELO) method. The UV laser diodes lased in the peak wavelength range from 355.4 to 361.6 nm under a pulsed current operation at room temperature. We have also investigated both parameters, material gain and optical-internal loss in GaN/AlGaN multiple quantum wells (MQWs). The actual threshold currents of the UV laser diodes were practically in agreement with the estimated threshold current from these parameters. This layer structure is one of the solutions for the purpose of high-yield production of UV photonic devices.
Lasing at exciton transition in optically pumped gallium nitride nanopillars.
We report the observation of room temperature lasing action in optically pumped GaN nanopillars. The nanopillars were fabricated by patterned etching and crystalline regrowth from a GaN substrate. When nanopillars were optically excited, a narrow emission peak emerged from the broad spontaneous emission background. The increasing rate is nine times faster than that of the spontaneous emission background, showing the onset of lasing action. The lasing occurs right at the center of spontaneous emission rather than the often reported redshifted wavelength. A spectroscopic ellipsometry analysis indicates that the gain of lasing action is provided by exciton transition.