Reiko Soejima

InGaN Laser Diode Grown on 6H–SiC Substrate Using Low-Pressure Metal Organic Vapor Phase Epitaxy

InGaN multiple quantum well (MQW) laser diodes were fabricated on (0001)Si oriented 6H–SiC substrate using low-pressure metal organic vapor phase epitaxy (LP-MOVPE). The laser oscillation was observed above the threshold current of 800 mA at a peak wavelength of 414.3 nm under pulsed current injection at room-temperature. The pulse duration was 300 ns and the repetition frequency was 1 kHz. The threshold current density and differential efficiency were estimated to be 16 kA/cm2 and 0.03 W/A, respectively. The full width at half maximum (FWHM) of the lasing emission lines was between 0.03 nm and 0.21 nm. Streak-shaped far field patterns were clearly observable. The lifetime of the laser diode was more than 5 hours.

Interwell inhomogeneity of carrier injection in InGaN/GaN/AlGaN multiquantum well lasers

A simulation of current flow for an InGaN/GaN/AlGaN multiquantum well (MQW) laser showed that generation of the optical gain is inhomogeneous across the MQW due to inhomogeneous carrier injection. Laser diodes with three and five wells in MQW were compared to experimentally investigate inhomogeneous carrier injection. We found that external quantum efficiency was significantly improved by a reduction in the number of wells from five to three. The result was explained quantitatively by the fact that the five-well laser had a larger internal loss and a poorer internal quantum efficiency due to the inhomogeneous carrier injection.

Room-Temperature Continuous Wave Operation of InGaN Laser Diodes with Vertical Conducting Structure on SiC Substrate

We demonstrated for the first time room-temperature continuous wave operation of InGaN laser diodes with a vertical conducting structure fabricated on a SiC substrate. The threshold current and voltage were 84 mA and 12 V, respectiely, under pulsed operation. The threshold current corresponds to a threshold current density of 5.6 kA/cm2, which is the lowest ever reported with InGaN laser diodes on a SiC substrate. Under continuous wave operation, the threshold current and voltage were 115 mA and 10.5 V, respectiely. The peak lasing wavelength was 408.2 nm. Longitudinal modes of the optical cavity were clearly obsered. The laser oscillation was obsered up to 40°C under CW operation.

CONTINUOUS WAVE OPERATION AT ROOM TEMPERATURE OF INGAN LASER DIODES FABRICATED ON 4H-SIC SUBSTRATES

We demonstrated continuous wave operation at room temperature of InGaN laser diodes fabricated on 4H-SiC substrates. The threshold current and voltage were 60 mA and 8.3 V, respectively. The threshold current corresponds to a threshold current density of 4 kA/cm2. No difference in the threshold current or voltage was observed between 4H-SiC and 6H-SiC substrates. The laser oscillation was observed up to 80°C for CW operation. The peak lasing wavelength was 404.4 nm. The lifetime was 57 hours under automatic power controlled conditions with a constant output power of 1 mW at 25°C.

InGaN Laser Diodes Grown on SiC Substrate Using Low-Pressure Metal-Organic Vapor Phase Epitaxy

We report the crystal growth and the characteristics of InGaN multiple quantum well (MQW) laser diodes grown on a 6H-SiC substrate using a low-pressure metalorganic vapor phase epitaxy (LP-MOVPE). We discuss the buffer layer, the control of InGaN and AlGaN alloy composition, the magnesium doping of GaN and AlGaN, and the characteristics of the MQW structure. We also demonstrate the room-temperature pulsed operation of the laser diode. The threshold voltage was reduced to 15 V by improving the p-contact resistance. The threshold current was reduced to 500 mA by changing the MQW structure and employing high reflection coating.

Continuous-Wave Operation at 250 K of InGaN Multiple Quantum Well Laser Diodes Grown on 6H-SiC with Vertical Conducting Structure.

We demonstrated continuous-wave operation at 250 K of InGaN multiple quantum well laser diodes that were grown on 6H-SiC and had a vertical conducting structure in which p-type and n-type electrodes were formed at the top and the bottom of the chip, respectively. The threshold current, threshold voltage, and threshold current density were 380 mA, 12.6 V, and 12 kA/cm2, respectively. The laser diodes were operated at room temperature with a duty ratio up to about 20% at a repetition frequency of 1 kHz.

Properties of GaN epitaxial layer grown by MOVPE on MgAl{sub 2}O{sub 4} substrate

The authors propose a MgAl{sub 2}O{sub 4} substrate for GaN-based laser diodes. They grew GaN epitaxial layers using metal-organic vapor phase epitaxy on a MgAl{sub 2}O{sub 4} substrate. The GaN on the MgAl{sub 2}O{sub 4} showed a narrow X-ray diffraction peak of 310 arcsec, a photoluminescence dominated by the band-edge emission, and good electronic properties. The optical cavity was fabricated by cleaving the GaN on the MgAl{sub 2}O{sub 4}, and the stimulated emission from the cavity using optical pumping was observed. They also fabricated a light emitting diode (LED) with a AlGaN/InGaN double-heterostructure. The electroluminescence was dominated by the band-edge emission of InGaN with a narrow FWHM of 13.5 nm. The characteristics of LED on the MgAl{sub 2}O{sub 4} were comparable to that on a Al{sub 2}O{sub 3} substrate. MgAl{sub 2}O{sub 4} is feasible as a substrate for laser applications.