Shin-ichi Nagahama

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.

High‐power InGaN single‐quantum‐well‐structure blue and violet light‐emitting diodes

High‐power blue and violet light‐emitting diodes(LEDs) based on III–V nitrides were grown by metalorganic chemical vapor deposition on sapphire substrates. As an active layer, the InGaN single‐quantum‐well‐structure was used. The violet LEDs produced 5.6 mW at 20 mA, with a sharp peak of light output at 405 nm, and exhibited an external quantum efficiency of 9.2%. The blue LEDs produced 4.8 mW at 20 mA and sharply peaked at 450 nm, corresponding to an external quantum efficiency of 8.7%. These values of the output power and the quantum efficiencies are the highest ever reported for violet and blue LEDs.

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 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.

Blue InGaN-based laser diodes with an emission wavelength of 450 nm

Blue InGaN single-quantum-well-structure laser diodes (LDs) with an emission wavelength of 450 nm were grown on an epitaxially laterally overgrown GaN substrate by a metalorganic chemical vapor deposition method. The threshold current density and voltage were 4.6 kA cm−2 and 6.1 V, respectively. The estimated lifetime was approximately 200 h under room-temperature continuous-wave operation at an output power of 5 mW. When the number of InGaN well layers of the LDs with emission wavelengths longer than 435 nm varied from one to three, the lowest threshold current density was obtained when the number of well layers was one.

510–515 nm InGaN-Based Green Laser Diodes on c-Plane GaN Substrate

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.

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.