Nanowire AlGaN/GaN core-shell UV LEDs 5x brighter than GaN counterparts
As described in the Nanotechnology journal, in a paper titled “UV LEDs Based on p-i-n Core-Shell AlGaN/GaN Nanowire Heterostructures Grown by N-polar Selective Area Epitaxy”, the brighter LEDs are fabricated from nanowires with a so-called “p-i-n” structure, a tri-layer design that injects electrons and holes into the nanowire. The addition of aluminium to the shell helps confine electrons to the nanowire core, boosting the electroluminescence fivefold.
The authors attribute the improved characteristics to the localization of spontaneous recombination to the NW core, reducing carrier overflow losses through the NW shell, and eliminating current shunting.
“The role of the aluminium is to introduce an asymmetry in the electrical current that prevents electrons from flowing into the shell layer, which would reduce efficiency, and instead confines electrons and holes to the nanowire core,” first author Matt Brubaker explains on the NIST website.
The nanowire test structures were about 440nm long with a shell thickness of about 40nm. The final LEDs, including the shells, were almost 10 times larger. Researchers found that the amount of aluminium incorporated into fabricated structures is dependent on nanowire diameter.
According to group leader Kris Bertness, at least two companies are developing micro-LEDs based on nanowires, and NIST has a Cooperative Research and Development Agreement with one of them to develop dopant and structural characterization methods. The researchers have had preliminary discussions with scanning-probe companies about using NIST LEDs in their probe tips, and NIST plans to demonstrate prototype LED tools soon.
The NIST team also holds U.S. Patent 8,484,756 on an instrument that combines microwave scanning probe microscopy with an LED for non-destructive, contactless testing of material quality for important semiconductor nanostructures such as transistor channels and individual grains in solar cells. The probe could also be used for biological research on protein unfolding and cell structure.
NIST – www.nist.gov
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