Mark Teepe

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.

Ultraviolet semiconductor laser diodes on bulk AlN

Current-injection ultraviolet lasers are demonstrated on low-dislocation-density bulk AlN substrates. The AlGaInN heterostructures were grown by metalorganic chemical vapor deposition. Requisite smooth surface morphologies were obtained by growing on near-c-plane AlN substrates, with a nominal off-axis orientation of less than 0.5°. Lasing was obtained from gain-guided laser diodes with uncoated facets and cavity lengths ranging from 200 to 1500 μm. Threshold current densities as low as 13 kA/cm2 were achieved for laser emission wavelengths as short as 368 nm, under pulsed operation. The maximum light output power was near 300 mW with a differential quantum efficiency of 6.7%. This (first) demonstration of nitride laser diodes on bulk AlN substrates suggests the feasibility of using such substrates to realize nitride laser diodes emitting from the near to deep ultraviolet spectral regions.

Continuous-wave InGaN multiple-quantum-well laser diodes on copper substrates

Continuous-wave (cw) indium-gallium nitride multiple-quantum-well laser diodes (LDs) were transferred from sapphire onto copper substrates using a two-step laser lift-off process. Reduced threshold currents and increased differential quantum efficiencies were measured for LDs on Cu due to a 50% reduction of the thermal impedance. Light output for LDs on Cu was three times greater than comparable LDs on sapphire with a maximum output of 30 mW. CW operation was possible up to heatsink temperatures of 90 °C for LDs on Cu.

ROOM-TEMPERATURE CONTINUOUS-WAVE OPERATION OF INGAN MULTIPLE-QUANTUM-WELL LASER DIODES WITH AN ASYMMETRIC WAVEGUIDE STRUCTURE

Room-temperature continuous-wave (cw) operation is demonstrated with InGaN multiple-quantum-well laser diodes containing an asymmetric waveguide structure. Pulsed threshold current densities as low as 5.2 kA/cm2 have been obtained for ridge-waveguide laser diodes grown on sapphire substrates by metal-organic chemical vapor deposition. For improved thermal management, the sapphire substrate was thinned and the devices were mounted p side up onto a copper heatsink. Under cw conditions at 20 °C, threshold current densities were 8.3 kA/cm2 with threshold voltages of 6.3 V. The emission wavelength was 401 nm with output powers greater than 3 mW per facet. Under cw conditions, laser oscillation was observed up to 25 °C. The room-temperature cw operation lifetimes, for a constant current, exceeded one hour.

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%.

Performance and degradation of continuous-wave InGaN multiple-quantum-well laser diodes on epitaxially laterally overgrown GaN substrates

The performance and degradation characteristics of continuous-wave (cw) InGaN multiple-quantum-well laser diodes are reported. A cw threshold current as low as 62 mA was obtained for ridge-waveguide laser diodes on epitaxially laterally overgrown GaN on sapphire substrates grown by metalorganic chemical vapor deposition. Transmission electron microscopy reveals a defect density <5×107 cm−2 in the active region. The emission wavelength was near 400 nm with output powers greater than 20 mW per facet. Under cw conditions, laser oscillation was observed up to 70 °C. The room-temperature cw operation lifetimes, measured at a constant output power of 2 mW, exceeded 15 h. From the temperature dependence of the laser diode lifetimes, an activation energy of 0.50 eV±0.05 eV was determined.

Ultraviolet InAlGaN Light Emitting Diodes Grown on Hydride Vapor Phase Epitaxy AlGaN/Sapphire Templates

We demonstrate high-efficiency UV InAlGaN multiple-quantum-well light-emitting diodes (LED) deposited by metal–organic chemical vapor deposition (MOCVD) on hydride vapor phase epitaxy (HVPE) grown AlGaN/sapphire templates. The combination of HVPE and MOCVD allows the separate optimization of the growth of high-quality AlGaN/sapphire templates and sophisticated LED heterostructures. High-performance UV LEDs emitting in the range between 373 and 289 nm have been realized. LED devices emitting near 330 nm exhibit cw light output power of more than 11 mW and an external quantum efficiency (EQE) of 1.5%. Under pulsed bias testing, peak light output is more than 55 mW with an EQE of 2.3%.

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.

Continuous-wave operation of InGaN multiple quantum well laser diodes on copper substrates obtained by laser lift-off

In recent years tremendous progress has been made in the development of AlGaInN laser diodes (LDs) and the commercialization of violet laser diodes has just recently begun. An important factor in order to improve laser diode performance and lifetime was the reduction of the dislocation density in the GaN material. In this paper we will report on the performance characteristics of cw laser diodes grown by metal organic chemical vapor deposition on laterally epitaxially overgrown GaN on sapphire substrates (ELOG). The InGaAlN films were processed into ridge-waveguide lasers with CAIBE etched mirrors and a high reflective coating on the backside facet.