Researchers from the University of Sheffield a new fabrication process for green InGaN microLEDs that achieves high brightness compact microLED arrays.

Emission microscopy of efficient InGaN green microLEDs (University of Sheffield)

Today most green InGaN microLEDs are produced by combining a standard photolithography technique with subsequent dry-etching processes on a standard III-nitride LED wafer. The researchers found a way to avoid the dry-etching processes which damage the surface the resulting LEDs. In the new process, the InGaN stack is direectly grown within pre-patterned micro-hole arrays through a thin (500nm) SiO2 layer serving as a GaN template over the epitaxial wafer.

The researchers use metalorganic vapour-phase epitaxy (MOVPE) to fabricate the individual microLEDs which are selectively overgrown within each micro-hole. The micro-hole masks offer a natural surface passivation around each microLED which can greatly simplify the device fabrication. All the μLEDs in the array share a common n-contact, while all the p-contacts are left open, which can then be contacted either individually or across large areas.

The researcher produced a few thousand 3.6 μm micro-LEDs, arrayed across a 0.1 mm2 surface and calculated that an individual 3.6 μm microLED could be brightly lit at an ultra-low driving current of 0.3 μA under a 2.5V bias. A 640x480 pixels display built around such LEDs would only draw 0.23W.

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