At room temperature, cleaved-facet nitride diode lasers produce 160 mW at 410 nm
Advancing the drive toward blue-output diode lasers, Shuji Nakamura and colleagues at Nichia Chemical Industries Ltd. (Kaminaka, Japan) have created indium gallium nitride/gallium nitride/aluminum gallium nitride (InGaN/GaN/AlGaN) diode lasers on GaN substrates, which are easily cleaved and have a high thermal conductivity. Previous InGaN lasers developed by Nichia have demonstrated lifetimes of 10,000 hours but have been grown on a sapphire substrate, which is difficult to cleave and does not efficiently dissipate heat.
In this case, a GaN substrate was first grown on a sapphire substrate by metal-organic chemical-vapor deposition (MOCVD) followed by hydride vapor-phase epitaxy. The 150-µm-thick GaN substrate was then removed, and an InGaN multiple-quantum-well-structure diode laser was grown on it by MOCVD. The diode with cleaved-mirror facets produced up to 160 mW under room-temperature continuous-wave operation at about 410 nm. Because of the high threshold-current density, the lifetime at a constant output power of 5 mW was only approximately 180 hours. The researchers expect longer lifetimes if the threshold current can be reduced to 1-4 kA/cm2.