Hiroyuki Kiyoku

InGaN/GaN/AlGaN-based laser diodes with modulation-doped strained-layer superlattices grown on an epitaxially laterally overgrown GaN substrate

InGaN multi-quantum-well-structure laser diodes with Al0.14Ga0.86N/GaN modulation doped strained-layer superlattice cladding layers grown on an epitaxially laterally overgrown GaN (ELOG) substrate was demonstrated to have a lifetime of more than 1150 h under room-temperature continuous-wave operation. After 4 μm etching of the ELOG substrate, the etch pit density was about 2×108 cm2 in the region of the 4-μm-wide stripe window, but almost zero in the region of the 7-μm-wide SiO2 stripe.

Room‐temperature continuous‐wave operation of InGaN multi‐quantum‐well structure laser diodes

Continuous‐wave (cw) operation of InGaN multi‐quantum‐well structure laser diodes (LDs) was demonstrated at room temperature (RT). The threshold current and voltage of the LD were 130 mA and 8 V, respectively. The threshold carrier density was 9 kA/cm2. The lifetime of the LDs under RT cw operation was 1 s due to large heat generation. Mode hopping of the emission wavelength of the LDs was observed. The average wavelength drift due to temperature increase was 0.066 nm/K between 20 and 70 °C, because of the temperature dependence of the gain profile due to band‐gap narrowing of the InGaN active layer.

InGaN/GaN/AlGaN-Based Laser Diodes with Modulation-Doped Strained-Layer Superlattices

InGaN multi-quantum-well-structure laser diodes with Al0.14Ga0.86N/GaN modulation doped strained-layer superlattice cladding layers grown on an epitaxially laterally overgrown GaN substrate were demonstrated to have an estimated lifetime of more than 10000 h under continuous-wave operation at 20° C. Under operation at a high temperature of 50° C, the lifetime was longer than 1000 h. With the operating current increasing to above the threshold, a self-pulsation with a high frequency of 3.5 GHz was observed. The carrier lifetime was estimated to be 1.8 ns from the pulsed modulation of the LDs.

Continuous-wave operation of InGaN/GaN/AlGaN-based laser diodes grown on GaN substrates

InGaN multi-quantum-well-structure laser diodes (LDs) grown on GaN substrates were demonstrated. The LDs showed a small thermal resistance of 30 °C/W and a lifetime longer than 780 h despite a large threshold current density of 7 kA/cm2. In contrast, the LDs grown on a sapphire substrate exhibited a high thermal resistance of 60 °C/W and a short lifetime of 200 h under room-temperature continuous-wave operation.

ROOM-TEMPERATURE CONTINUOUS-WAVE OPERATION OF INGAN MULTI-QUANTUM-WELL STRUCTURE LASER DIODES WITH A LIFETIME OF 27 HOURS

The continuous-wave (cw) operation of InGaN multi-quantum-well structure laser diodes (LDs) was demonstrated at room temperature (RT) with a lifetime of 27 h. The threshold current and the voltage of the LDs were 80 mA and 5.5 V, respectively. The threshold current density was 3.6 kA/cm2. Longitudinal modes with a mode separation of 0.042 nm were observed under cw operation at RT. When the temperature of the LDs was varied, large mode hopping of the emission wavelength was observed between adjacent quantum well or quantum dot subbands. The carrier lifetime and the threshold carrier density were estimated to be 10 ns and 2×1020/cm3, respectively.

InGaN Multi-Quantum-Well-Structure Laser Diodes with Cleaved Mirror Cavity Facets

InGaN multi-quantum-well (MQW)-structure laser diodes (LDs) fabricated from III–V nitride materials were grown by metalorganic chemical vapor deposition on sapphire substrate with (11*BAR*2*BAR*0) orientation (A face). The mirror facet for a laser cavity was formed by cleaving the substrate along the (1*BAR*1*BAR*02) orientation (R-face). As an active layer, the InGaN MQW structure was used. The InGaN MQW LDs showed a sharp peak of light output at 415.6 nm that had a full width at half-maximum of 0.05 nm under pulsed current injection of 1.17 A at room temperature. The laser threshold current density was 9.6 kA/cm2.

InGaN multi‐quantum‐well structure laser diodes grown on MgAl2O4 substrates

InGaN multi‐quantum‐well (MQW) structure laser diodes fabricated from III‐V nitride materials were grown by metalorganic chemical vapor deposition on (111) MgAl2O4 substrates. The mirror facet for a laser cavity was formed by polishing III‐V nitride films grown on (111) MgAl2O4 substrates. As an active layer, the InGaN MQW structure was used. The laser threshold current density was 8 kA/cm2. At a current above laser threshold, stimulated emission was observed with a sharp peak of light output at 410 nm that had a full width at half‐maximum of 2.1 nm under pulsed current injection at room temperature.

High-Power, Long-Lifetime InGaN/GaN/AlGaN-Based Laser Diodes Grown on Pure GaN Substrates

Epitaxially laterally overgrown GaN on sapphire was used to reduce the number of threading dislocations originating from the interface of the GaN epilayer with the sapphire substrate. The GaN layer above the SiO2 mask area surrounding the window, corresponding to the lateral overgrowth, was nearly free of the threading dislocations. A high density of threading dislocations was observed in the vicinity of GaN grown in the window regions. InGaN multi-quantum-well-structure laser diodes (LDs) grown on pure GaN substrates, which were fabricated by removing the sapphire substrate, were demonstrated. The LDs with an output power of 5 mW exhibited a lifetime of more than 290 h and an estimated lifetime of 10,000 h despite a relatively large threshold current density. The far-field pattern of the LDs with a cleaved mirror facet revealed single-mode emission without any interference effects.

High-Power, Long-Lifetime InGaN Multi-Quantum-Well-Structure Laser Diodes

The continuous-wave operation of InGaN multi-quantum-well structure laser diodes (LDs) was demonstrated at room temperature with a high output power of 50 mW, a high operating temperature of 100° C and a long lifetime of 300 hours. The characteristic temperature of the threshold current was as high as 170 K. The emission wavelength of the LDs was 416 nm.

Room-temperature continuous-wave operation of InGaN multi-quantum-well-structure laser diodes with a long lifetime

The continuous-wave operation of InGaN multi-quantum-well-structure laser diodes (LDs) was demonstrated at room temperature with a lifetime of 24–40 min. The threshold current and the voltage of the LDs were 80 mA and 6.5 V, respectively. The laser emission was a fundamental single-mode emission with a peak wavelength of 400.23 nm and a full width at half-maximum of 0.002 nm. The beam full width at half-power values for the parallel and the perpendicular near-field patterns were 1.6 and 0.8 μm, respectively. Those of the far-field patterns were 6.8° and 33.6°, respectively. The carrier lifetime and the threshold carrier density were estimated to be 5 ns and 1×1020/cm3, respectively.