Current status of GaN-based multiple quantum well laser diodes

We have improved the characteristics of GaN-based multiple quantum well (MQW) laser diodes (LDs) grown on sapphire substrates in terms of crystal defect reduction by the lateral epitaxial growth (LEG) method, smoothing the LDs' facets fabricated by the cleaving technique, and promoting thermal dissipation by junction-down bonding. The threshold current has been reduced to 36 mA. The relative intensity noise (RIN) value was -130 dB/Hz, which corresponds to next-generation DVD systems. Output power up to 150 mW was obtained with no kink. After that, we applied GaN substrates for improving the LDs' characteristics further. The threshold current has been reduced to 31 mA. The slope efficiency was 1.5 W/A, which is higher than that for sapphire substrates with LEG layer.