UV LEDs are used in a growing number of applications such as polymer curing, water purification and medical disinfection. Researchers at NIST have been trying to make nanowire-based LEDs for scanning-probe tips intended for electronics and biology applications. Lately, researchers have been experimenting with nanowire cores made of silicon-doped GaN, which has extra electrons, surrounded by shells made of magnesium-doped GaN, which has a surplus of “holes” for missing electrons. When an electron and a hole combine, energy is released as light, a process known as electroluminescence.
The research was published in the Nanotechnology Journal with title “UV LEDs Based on p-i-n Core-Shell AlGaN/GaN Nanowire Heterostructures Grown by N-polar Selective Area Epitaxy.” As described article, 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 aluminum to the shell helps confine electrons to the nanowire core, boosting the electroluminescence fivefold.
“The role of the aluminum 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,” explained first author Matt Brubaker.
The nanowire test structures were about 440 nanometers (nm) long with a shell thickness of about 40 nm. The final LEDs, including the shells, were almost 10 times larger. Researchers found that the amount of aluminum incorporated into fabricated structures depends on nanowire diameter.
Group leader Kris Bertness said 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.