Naoko Miyashita

Current-injection spiral-shaped microcavity disk laser diodes with unidirectional emission

A spiral-shaped microcavity heterojunction laser diode fabricated with InGaN multiple quantum wells is demonstrated to operate under current injection conditions and emit unidirectionally. Room-temperature laser operation was achieved for microcavity disk radii ranging from 50 to 350 μm and threshold current densities as low as 4.6 kA/cm2. Unidirectional laser emission is clearly revealed in the far-field pattern with the lateral divergence angle ranging from 60° to 75°. Output power of more than 25 mW was obtained for emission wavelengths near 400 nm.

Continuous-wave operation of ultraviolet InGaN/InAlGaN multiple-quantum-well laser diodes

We demonstrate ultraviolet InGaN/InAlGaN multiple-quantum-well laser diodes operating under continuous-wave (cw) conditions. The laser diodes were grown on sapphire substrates by metalorganic chemical vapor deposition. Under pulsed bias conditions, we have achieved threshold current densities as low as 5 kA/cm2 for laser diodes with emission wavelengths between 368 nm and 378 nm and have demonstrated lasing at 363.2 nm at room temperature, the shortest wavelength yet reported for a semiconductor laser diode. The cw operation up to a heat sink temperature of 40 °C was demonstrated on a series of narrow ridge-waveguide devices processed with chemically assisted ion beam etched mirrors and high reflective coating on both facets. The shortest wavelength emission under cw operation conditions was 373.5 nm with output powers of more than 1 mW.

Ultraviolet AlGaN multiple-quantum-well laser diodes

We demonstrate ultraviolet emission from current-injection AlGaN multiple-quantum-well laser diodes grown on sapphire substrates by metalorganic chemical vapor deposition. Lasing was obtained in gain-guided laser diode test structures with uncoated facets and cavity length ranging from 400 to 1500 μm. Under pulsed bias conditions, threshold current densities as low as 23 kA/cm2 have been achieved for laser diodes with emission wavelengths between 359.7 and 361.6 nm. The maximum output power was 45 mW per facet with differential quantum efficiencies of 1.3%.

Two-section InGaN multiple-quantum-well laser diode with integrated electroabsorption modulator

Q-switching is demonstrated in a two-section InGaN multiple-quantum-well (MQW) laser diode consisting of an electroabsorption modulator and amplifier (gain) section. The modulator and gain sections are optically coupled and share the same InGaN MQW active region, but they are electrically separated by a narrow dry-etched trench. Applying a reverse bias voltage to the modulator section controls the absorption in the modulator portion of the device by compensating the piezoelectric field in the InGaN quantum wells. Changes in the absorption coefficient as large as 5000 cm−1 were realized with a moderate reverse bias of 7.2 V. By forward biasing, the amplifier section at a constant current of 225 mA and by controlling the reverse bias modulator voltage, the output power of the two-section laser diode could be switched between <0.5 mW (off state) and more than 3 mW (on state) with a laser emission wavelength near 401 nm.

CW InGaN Multiple-Quantum-Well Laser Diodes on Copper Substrates

Continuous-wave (cw) InGaN multiple-quantum-well laser diodes grown on sapphire substrates by metalorganic chemical vapor deposition (MOCVD) were successfully transferred onto copper using an excimer laser lift-off technique. For the laser diodes on copper substrates improved device performance was observed with room-temperature cw threshold currents as low as 68 mA and threshold voltages of 5.9 V. Differential quantum efficiencies of 0.7 W/A were obtained with a laser emission wavelength near 400 nm. GaN-based laser structures transferred onto copper substrates show a significantly reduced thermal resistance resulting in a more than twofold increase in cw output power to more than 100 W. High quality cleaved facets have been obtained for freestanding GaN laser membranes after sapphire substrate removal.

CW InGaN multiple-quantum-well laser diodes on copper and diamond substrates by laser lift-off

Abstract Continuous-wave (cw) InGaN multiple-quantum-well laser diodes grown on sapphire substrates by metalorganic chemical vapor deposition were successfully transferred onto copper and diamond using excimer laser lift-off. Room-temperature cw threshold currents as low as 87 mA with threshold voltages of 5.8 V were obtained for laser diodes on diamond substrates. GaN-based laser structures transferred onto Cu substrates show a significantly reduced thermal resistance resulting in a more than 2× increase in cw output power of more than 100 mW. High-quality cleaved facet have been obtained for free-standing GaN laser membranes after sapphire substrate removal.

Continuous-wave InGaN laser diodes on copper and diamond substrates

InGaN-based optoelectronics were integrated with dissimilar substrate materials using a novel thin-film laser lift-off (LLO) process. The LLO process was employed to integrate InGaN-based laser diodes (LDs) with Cu and diamond substrates. Separation of InGaN-based thin-film devices from their typical sapphire growth substrates was accomplished using a pulsed excimer laser in the ultraviolet regime incident through the transparent substrate. Characterization of the LDs before and after the sapphire substrate removal revealed no measurable degradation in device performance. Reduced threshold currents and increased differential quantum efficiences were measured for LDs on Cu due to a 50% reduction of the thermal impedence. Light output for LDs on Cu was two times greater than comparable LDs on sapphire with a maximum output of 100 mW. Increased light output for LDs on diamond was also measured with a maximum output of 80 mW.

Spiral‐shaped microcavity laser: a new class of semiconductor laser

A spiral‐shaped microcavity structure is used to achieve uni‐direcitonal laser emission from a microresonator. This was previously demonstrated with an InGaN MQW microdisk laser emitting near 400 nm and is demonstrated here with room‐temperature laser operation of an AlGaAs heterostructure with pulsed threshold current densities as low as 400 A/cm2, emission wavelength near 730 nm, and output power of more than 4 mW. Continuous‐wave operation of an AlGaAs microdisk laser is also demonstrated for a disk radius of 50 μm.

Ultraviolet InGaN, AlGaN, and InAIGaN multiple-quantum-well laser diodes

Design and performance characteristics of InGaN, AlGaN and InAlGaN multiple quantum well (MQW) laser diodes emitting in the ultraviolet spectral region are reported. The nitride laser diodes were grown on quasi-bulk GaN and c-plane sapphire substrates by metalorganic chemical vapor deposition. By reducing the indium content in the InGaN MQW, we have realized laser diodes on GaN substrates emitting at wavelength as short as 366.9 nm with pulsed threshold current densities around 8kA/cm2. Improved performance characteristic with differential quantum efficiencies of 7.7% and light output powers of close to 400mW were obtained. We also demonstrate room-temperature pulsed operation of AlGaN and InAlGaN MQW laser diodes grown on sapphire substrates emitting at a record short wavelength of 357.9nm. Light output powers greater than 80mW under pulsed current-injection conditions and differential quantum efficiencies of 4.2% have been achieved.

Advances in InAlGaN laser diode technology toward the development of UV optical sources

We report on ultraviolet (UV) InGaN and GaN multiple quantum well (MQW) laser diodes grown on c-plane sapphire substrates by metal organic chemical vapor deposition. By reducing the indium content in the InGaN/InAlGaN MQW, we have systematically pushed the room-temperature laser emission to a record low wavelength of 363.2nm. Pulsed threshold current densities around 5 kA/cm2 have been achieved for laser diodes with emission wavelength between 368 nm and 378 nm. Light output powers greater than 400mW under pulsed current-injection conditions (pulse duration 500 ns, repetition frequency 1 kHz) and differential quantum efficiencies of 4.8% have been achieved. We also demonstrate room-temperature continuous-wave operation of ridge-waveguide devices with threshold currents of 85 mA for an emission wavelength of 377.8 nm and output power of more than 3 mW.