- Researchers use nanowires and a special type of shell to build ultraviolet light-emitting diodes.
- They produce 5 times higher light intensity than LEDs based on conventional shell design.
Ultraviolet light-emitting diodes (UV LEDs) are used in an increasing number of applications such as water purification, spectroscopy, photopolymer curing, and medical disinfection.
Deep UV LEDs based on nanowires have gained a lot of attention recently, as they can provide new functionalities related to their nanoscale size and discrete nature. For instance, single-nanowire LEDs can be used to build new systems for sub-diffraction optical lithography, which could be scaled up into pixelated arrays for wafer-level lithography.
Recently, researchers at National Institute of Standards and Technology used a special type of shell to develop nanowire-based UV LEDs that produce 5 times higher light intensity than LEDs based on a conventional shell design.
How Did They Do It?
Lately, the team has been working on nanowire cores made of silicon-doped Gallium Nitrate (contains extra electrons) enclosed by shells made of magnesium-doped Gallium Nitrate (contains a surplus ‘holes’ for missing electrons). When a hole merges with an electron, a significant amount of energy is ejected in the form of light; this process is called electroluminescence.
In 2017, they revealed Gallium Nitrate LEDs that involved injecting electrons into the shell layer to merge with holes and ultimately produce high-intensity light. The new LEDs work in a similar manner, except this time researchers added a small amount of aluminum to the shell layer.
The aluminum minimizes the losses occurred due to electron overflow and light reabsorption. More specifically, it brings an asymmetry within the electrical current, preventing electrons from moving into the shell layer. This confines the holes and electrons to the core of the nanowire, which results in five times higher light intensity.
Nanowire-based LED | Incorporating a small amount of aluminum to shell layer (black) confines holes and electrons into the core of the nanowire (multicolored area), generating intense light | Courtesy of researchers
The researchers used a so-called “p-i-n” structure to fabricate LEDs from nanowires. The structure represents a tri-layer design for injecting electron and holes into the nanowire.
The more the diameter of a nanowire, the more aluminum can be incorporated into fabricated structures. The nanowire developed in this study had a length of 440 nanometers and a shell thickness of 40 nanometers. The resulting LEDs were nearly 10x larger.
Implementing The Technology
The team already holds a patent for a device that integrates LED with microwave scanning probe microscopy for safe, contactless testing of semiconductor nanostructures. It can also be used to study cell structure and protein unfolding.
While the structures explored in this work targeted the approximate composition needed for carrier confinement, a higher fraction of aluminum may help researchers configure wavelength and control emission/polarization in Gallium Nitrate core. However, that remains a subject of future work.
Currently, researchers are working with two private organizations to develop nanowire-based micro-LEDs. One of them has agreed to build dopant and structural characterization techniques. The team will soon demonstrate the prototype LED tools.