World highest wall plug efficiency 638-nm red high-power broad area laser diode

Laser displays require red, green, and blue Broad Area Laser Diodes (BA-LDs) for their light sources. The requirements for the LDs are high output with high wall plug efficiency (W.P.E.) Blue and green LDs consist of AlInGaN/GaN. The former has been reported with W.P.E. above 50%. The latter has low one around 24%, but the luminosity of the green light is quite high compared to blue and red, so the W.P.E doesn’t become a big problem so far. The red color shows lower luminosity as the wavelength gets longer. Therefore, short wavelengths such as 638 nm are chosen for red LD for the display. The highest one of 42% at CW operation, 25°C, was reported by other two researchers so far in this wavelength BA-LDs. We developed the 638-nm BA-LD. The LD chip had a similar stripe geometry to the reported one with a cavity length of 1.5 mm and dual stripe geometry with a stripe width of 75 μm each. A window-mirror structure was also implemented, and the chip was mounted on a Φ9 TO-can in a junction-down configuration. As a result, the peak W.P.E of 42.3% was achieved, 0.3 points higher than the previous report. The power dissipation related to the threshold current accounts for a large part of the total dissipation. Each stripe width of 60 μm was chosen to reduce the threshold current, and the LD showed the world’s highest of 44.9% under this condition. This value was approximately 7% (2.9 points) higher than the reported value.