High-power GaN-based edge-emitting laser diodes

This report describes the latest developments in gallium nitride (GaN)-based edge-emitting laser diodes (LDs). We have been engaged in the development of blue LDs for display applications for many years. The epitaxial layers of the LDs were grown on c-plane free-standing GaN substrates by metal organic chemical vapor deposition (MOCVD), and a ridge type structure was formed at the top of the p-type layers. The fabricated LDs were mounted on a heatsink using a junction-down method in a TO-9 (ø9mm) package. We optimized the epitaxial layers and device structure, which led to an improvement of the optical output power and wall-plug efficiency (WPE) of the LDs. The WPE of the blue LD reached 53.2%, with an optical output power of 7.11W at a current of 3.5A under continuous-wave (CW) operation. This WPE is the highest reported for blue LDs to date. Additionally, we have been developing blue LDs for processing applications. Improving optical output power significantly is essential for applications such as copper welding and cutting. The cavity lengths and the ridge width of the LDs were modified, and by implementing these changes in a low thermal resistance package, we successfully increased the optical output power significantly. The WPE of the blue LD developed for copper processing reached 41.6%, with an optical output power of 26.8W at a current of 16.5A under CW operation. This is the highest optical output power from a single LD chip to our knowledge.