Takatoshi Ikegami

531 nm Green Lasing of InGaN Based Laser Diodes on Semi-Polar {2021} Free-Standing GaN Substrates

Lasing in pure green region around 520 nm of InGaN based laser diodes (LDs) on semi-polar {2021} free-standing GaN substrates was demonstrated under pulsed operation at room temperature. The longest lasing wavelength reached to 531 nm and typical threshold current density was 8.2 kA/cm2 for 520 nm LDs. Utilization of a novel {2021} plane enabled a fabrication of homogeneous InGaN quantum wells (QWs) even at high In composition, which is exhibited with narrower spectral widths of spontaneous emission from LDs than those on other planes. The high quality InGaN QWs on the {2021} plane advanced the realization of the green LDs.

Continuous-Wave Operation of 520 nm Green InGaN-Based Laser Diodes on Semi-Polar {2021} GaN Substrates

Room-temperature continuous-wave operation of 520 nm InGaN-based green laser diodes on semi-polar {2021} GaN substrates was demonstrated. A threshold current of 95 mA corresponding to a threshold current density of 7.9 kA/cm2 and a threshold voltage of 9.4 V were achieved by improving the quality of epitaxial layers on {2021} GaN substrates using lattice-matched quaternary InAlGaN cladding layers and also by adopting a ridge-waveguide laser structure.

High-Power (over 100 mW) Green Laser Diodes on Semipolar

Continuous-wave operation of InGaN green laser diodes (LDs) on semipolar {2021} GaN substrates with output powers of over 100 mW in the spectral region beyond 530 nm is demonstrated. Wall plug efficiencies (WPEs) as high as 7.0–8.9% are realized in the wavelength range of 525–532 nm, which exceed those reported for c-plane LDs. The longest lasing wavelength has reached 536.6 nm under cw operation. These results suggest that the InGaN green LDs on the {2021} plane are better suited as light sources for applications requiring wavelengths over 525 nm.

\{20\bar{2}1\}

Green laser diodes (LDs) on the {2021} plane exhibit lower threshold current densities, nearly half of those on the c-plane in the green region between 520–530 nm. The threshold current of a typical {2021} green LD lasing at 525.5 nm under room temperature cw operation is 51.1 mA, which corresponds to a threshold current density of 4.3 kA/cm2. The threshold voltage is 6.38 V. The characteristics temperature T0 is measured to be 175 K. The perpendicular θ⊥ and parallel θ|| beam divergence angles at half power of the {2021} green LDs are 24 and 11°, respectively. From the viewpoint of the device characteristics, especially the threshold current density, we conclude that the green LDs on the {2021} plane GaN substrates have the essential advantage for obtaining efficient green LDs.

GaN Substrates Operating at Wavelengths beyond 530 nm

True green GaInN laser diodes with a lasing wavelength above 525 nm under continuous wave operation have been successfully fabricated on semipolar {2021} GaN substrates by improving both the diode structure and epitaxial growth conditions. At a case temperature of 55 °C, their lifetime was estimated to be over 5000 h for an optical output power of 50 mW and over 2000 h at 70 mW.