InGaN Laser Diodes Grown by Molecular Beam Epitaxy
Despite its potential advantages over metallorganic chemical vapor deposition, molecular beam epitaxy has until recently been considered unsuitable for the production of InGaN-based emitters such as blue-violet laser diodes for next-generation optical data storage. Now a group of scientists at the Institute of High Pressure Physics in Warsaw, Poland, has used plasma-assisted molecular beam epitaxy to successfully fabricate 408-nm multiple-quantum-well laser diodes with device parameters comparable to early emitters grown by metallorganic chemical vapor deposition.
Last year, a team at Sharp Laboratories of Europe Ltd. in Oxford, UK, reported room-temperature pulsed operation from 400-nm InGaN-based laser diodes produced by molecular beam epitaxy, in which ammonia served as the nitrogen source. The use of ammonia, however, is accompanied by hazards and technological challenges, note the researchers behind the current work, who collaborated with a colleague at the National Research Council's Institute for Microstructural Sciences in Ottawa.
The researchers. led by Czeslaw Skierbiszewski, instead employed RF plasma-activated purified nitrogen gas as their source. High-pressure-grown bulk GaN with a dislocation density <100 cm22 served as the substrate, and the lasers were fabricated at growth temperatures of 710 and 590 °C in a custom reactor at the institute. The active region of the devices comprised five InGaN/InGaN:Si quantum wells.
In tests at room temperature under pulsed current injection, the lasers displayed multimode operation at a wavelength of 408 nm with a full width half maximum of approximately 0.4 nm. The threshold current was 900 mA at 9 V, and the maximum output power was 0.83 W under a current of 3.6 A and bias of 9.6 V.
The scientists suggest that the application of facet coatings will reduce the current and voltage at threshold. They also suggest that an optimized device design will offer sufficiently high internal quantum efficiencies for CW operation.
MORE FROM PHOTONICS MEDIA