AlN nanowall-based UV LEDs boast 60% internal quantum efficiency

September 12, 2017 // By Julien Happich
Researchers from the University of Michigan (US) and the McGill University (Canada) have demonstrated large area AlN nanowall light emitting diodes emitting at 214nm with an internal quantum efficiency as high as 60%.

The AlN nanowall LED stacks were built on top of GaN nanowall structures which were first created on an n-type GaN template on a sapphire substrate using e-beam lithography and dry etching techniques. Grown through molecular beam epitaxy (MBE), the AlN nanowall LEDs then consisted of Si-doped AlN, non-doped AlN, and Mg-doped AlN segments, with each layer being approximately 40nm thick. A 3nm p-GaN layer was deposited on the top surface to serve as p-contact with Ti/Au n-metal.

An AlN nanowall LED heterostructure grown on
a GaN template on a sapphire substrate.

Prior to growing the AlN nanowall LEDs, a 300 nm thick SiOx layer was first deposited on the GaN nanowall structures for surface passivation and electrical isolation, then p-Metal Ni/Au contacts were deposited through selectively etched areas.

The paper "Molecular beam epitaxial growth and characterization of AlN nanowall deep UV light emitting diodes" published in the Applied Physics Letters details various experiments with wall widths varying from 100nm to 1μm, noting a consistent blueshift in the emission wavelengths which the researchers explain by the reduced tensile strain distribution.