A low-cost surface emitting green laser

January 17, 2020 //By Julien Happich
green lasers
Designing conically-shaped core-shell InGaN/AlGaN multiple quantum disk (MQD) heterostructure nanocrystals within epitaxially-grown GaN nanowires, an international team of physicists from Canada, Korea and the USA has achieved a low-threshold surface-emitting semiconductor laser that outputs a green light when pumped electrically.

The results puplished under the title "An electrically pumped surface-emitting semiconductor green laser" in Science Advances detail an all-epitaxially grown device that exploits the photonic band edge modes formed in dislocation-free gallium nitride nanocrystal arrays, instead of using conventional distributed Bragg reflectors (DBRs).

Fig. 1: Schematics of the nanocrystal
surface-emitting laser (NCSEL) in
operation. Credit: Science Advances.

So far, room temperature surface-emitting green laser diodes relied on dual dielectric distributed Bragg reflectors (DBRs) and water bonding to a copper plate for low thermal resistance, but such devices exhibited a very large threshold current density at room temperature, and their light emission was limited to 400 and 460nm (violet blue).

Fig. 2: Schematic illustration of the full NCSEL fabrication, including passivation, planarization,
photolithography, and contact metallization techniques. Credit: Science Advances.

In contrast, the 10μm-diameter device operates at around 523nm and exhibits a threshold current of about 400A/cm2, over one order of magnitude lower compared to previously reported blue laser diodes. First explored through simulation, the so-called nanocrystal surface-emitting laser (NCSEL) was carefully engineered from InGaN/AlGaN (indium gallium nitride/aluminum gallium nitride) nanocrystal arrays of precisely controlled size, spacing and surface morphology.

The efficient strain relaxation in the conical core-shell InGaN/AlGaN multiple quantum disks within the nanowires ensured the nanostructures were free of dislocations.

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