Kazuhide Sumiyoshi

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.

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Vertical GaN Schottky barrier diodes (SBDs) were fabricated on freestanding GaN substrates with low dislocation density. High quality n-GaN drift-layer with an electron mobility of 930 cm2 V-1 s-1 was obtained by optimizing the growth conditions by reducing the intensity of yellow luminescence using conventional photoluminescence measurements. The specific on-resistance (RonA) and the breakdown voltage (VB) of the SBDs were 0.71 mΩ cm2 and over 1100 V, respectively. The figure of merit (VB2/RonA) was 1.7 GW/cm2, which is the highest value among previously reported SBDs for both GaN and SiC.

GaN Substrates Operating at Wavelengths beyond 530 nm

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.

Extremely Low On-Resistance and High Breakdown Voltage Observed in Vertical GaN Schottky Barrier Diodes with High-Mobility Drift Layers on Low-Dislocation-Density GaN Substrates

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.

Low Threshold Current Density InGaN Based 520–530 nm Green Laser Diodes on Semi-Polar {2021} Free-Standing GaN Substrates

Vertical GaN Schottky barrier diodes (SBDs) were fabricated on free-standing GaN substrates with low dislocation density. Vertical GaN-SBDs with a forward current of 5A and a blocking voltage of 600V exhibit the most superior reverse recovery characteristics among GaN, SiC, and Si diodes. We also confirmed stable forward and reverse aging characteristics for 1000 hours at 150 °C.