British experts use semipolar GaN growth of high efficiency LED

A team of researchers at Sheffield University in the United Kingdom recently published the latest in LEDs in semiconductors using the Physics Physics Letters on semipolar GaN or sapphire substrates .

Using microcolumn array templates made of GaN grown on M-Plane sapphire substrates, researchers are able to grow LEDs with higher quantum efficiency on semipolar GaN (11-22) overgrowth.

The research team's green LEDs grown on semipolar materials show that the blue shift of the emission wavelength decreases as the drive current increases compared to commercial LEDs grown on C-Plane sapphire substrates. The observed shift in blue shift also applies to yellow-green and yellow LEDs, so the researchers found that there is an effect in the growth of LEDs that effectively suppresses quantum yield while limiting star-dazzle.

(A) green (b) yellow-green (c) yellow (d) at 5mA, 20mA and 100mA, respectively Amber LED electroluminescence

The researchers measured the light source output as a linear increase in current rise on the wafer while its external quantum efficiency showed a significant improvement over the efficiency-droop of a commercial C-Plane LED. Electroluminescence Polarization measurements show that the polarization ratio of semi-polar LEDs is about 25%.

The researchers claim preliminary results show that overgrowth technology is a more cost-effective way to achieve high-performance semipolar GaN emitters over longer wavelengths.

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