We succeeded in developing InGaN-based green laser diodes (LDs) with a wavelength of 515 nm under continuous-wave (cw) operation by improving the growth condition of epitaxial layers and structures of LDs. The LD structures were grown on conventional c-plane free-standing GaN substrates by metal organic chemical vapor deposition (MOCVD). The threshold current and threshold voltage at 515 nm were 53 mA and 5.2 V, respectively. The lifetime of 510–513 nm LDs was estimated to be over 5000 h under cw operation with an optical output power of 5 mW at 25 °C.
InGaN multi-quantum-well-structure laser diodes (LDs) with an emission wavelength of longer than 420 nm were grown on both an epitaxially laterally overgrown GaN (ELOG) substrate and an ELOG on a free-standing GaN substrate by a metaorganic chemical vapor deposition method. The wavelength dependence of InGaN LD characteristics was investigated. It was found that there was a strong relationship between the threshold current density and the emission wavelength of LDs. The LDs with the emission wavelength of 450 nm grown on the ELOG on a free-standing GaN substrate were demonstrated. The threshold current density and voltage of these LDs were 2.8 kA/cm2 and 4.5 V, respectively. The estimated lifetime was approximately 5000 h under 50°C continuous-wave operation at an output power of 5 mW.
The ultraviolet laser diodes (LDs) whose active layers consisted of binary GaN were grown on epitaxially laterally overgrown GaN substrates by a metalorganic chemical vapor deposition method. For the first time, we observed the lasing emission from binary GaN active layer by current injection. The emission wavelength of GaN single quantum well LDs was 366.9 nm under pulsed current injection and 369.0 nm under continuos-wave (cw) operation at room temperature. The threshold current density and voltage of these LDs under the 25°C cw operation were 3.5 kA/cm2 and 4.6 V, respectively. The estimated lifetime was approximately 2000 h under 25°C cw operation at an output power of 2 mW.
InGaN multi-quantum-well-structure laser diodes (LDs), whose emission wavelengths are in the pure blue region, were grown on epitaxially laterally overgrown GaN on a free-standing GaN substrate by the metaorganic chemical-vapor deposition method. The wavelength dependence of the InGaN LD characteristics was investigated. These results indicated that there is a strong relationship between the threshold current density and the emission wavelength of LDs. LDs with an emission wavelength of 460 nm were demonstrated. The threshold current density and voltage of these LDs were 3.3 kA/cm2 and 4.6 V, respectively. The estimated lifetime was approximately 3000 h under 50 °C continuous-wave operation at an output power of 5 mW.
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