A research team at Sheffield University in the UK recently published the latest results in growing LEDs on semi-polar gallium nitride (GaN) or sapphire substrates in the journal Applied Physics Letter. .
Using micropillar array templates made of GaN grown on M-Plane sapphire substrates, researchers can grow LEDs with higher quantum benefits on semi-polar GaN (11-22) overgrown on them.
Compared to commercial LEDs grown on C-Plane sapphire substrates, the green light led by the research team on semi-polar materials shows that the blue shift of the emission wavelength decreases as the drive current increases. The situation observed in the blue shift is also applicable to the yellow-green and yellow-light LEDs. Therefore, the researchers found that the LEDs grown have an effect of effectively suppressing the quantum and limiting the starburst.
(a) green (b) yellow-green (C) yellow (d) amber LED electroluminescence image taken at 5 mA, 20 mA, and 100 mA, respectively
The researchers measured the source output as a linear increase with current on the wafer, while its external quantum efficiency showed a significant improvement in efficiency-droop compared to commercial C-Plane LEDs. Electroluminescence polarization measurements show that the polarization ratio of the semi-polar LED is about 25%.
The researchers claim that preliminary results show that overgrowth technology is a more potentially cost-effective way to achieve high-performance semi-polar GaN emitters in longer wavelength regions.
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