Development of highly efficient blue and green edge-emitting laser diodes

This report shows the latest developments of Gallium nitride (GaN)-based blue (455nm) and green (525nm) edge-emitting laser diodes (LDs). The epitaxial layers were grown on c-plane free-standing GaN substrates by metal-organic chemical vapor deposition (MOCVD), and a ridge-type structure for refractive-index waveguide was fabricated. Each LD chip was mounted on a heat sink in a TO-Φ9 mm CAN package by a junction down method for improving thermal dissipation. Optimization of epitaxial layers and device structures has led to improve the wall-plug efficiency (WPE) of LDs. The WPE and the optical output power of the blue LD have reached to 52.4% and 5.99 W at the current of 3.0 A under continuous wave (CW) operation, respectively. We also confirmed that the WPE and the optical output power of the green LD were 24.2 % and 1.90 W at the CW current of 1.9 A, respectively. Each WPE is the highest value ever reported of blue and green LDs. On top of this, the lifetime tests of both LDs over 1000 hours indicate the long lifetime more than 30,000 hours defined by the time when an optical output power is expected to be lower than the half of initial value.