Cleaning nanowires to get out more light

March 06, 2018

A technique for reducing the loss of light at the surface of semiconductor nanostructures has been demonstrated by scientists at KAUST.

Some materials can efficiently convert the electrons in an electrical current into light. These so-called semiconductors are used to create light-emitting diodes or LEDs: small, light, energy-efficient, long-lasting devices that are increasingly prevalent in both lighting and display applications.

The color, or wavelength, of the emitted light can be determined by choosing the appropriate material. Gallium arsenide, for example, emits predominantly infrared light. For shorter wavelengths that move into the blue or ultraviolet region of the spectrum, scientists have turned to gallium nitride. Then, to tune down the emission wavelength, aluminum can be added, which alters the spacing between the atoms and increases the energy bandgap.

However, numerous factors prevent all the radiation created in the semiconductor escaping the device to act as an efficient light source. Firstly, most semiconducting materials have a high refractive index, which makes semiconductor-air interfaces highly reflected--at some angles all light bounces backwards in a process known as total internal reflectivity. A second limitation is that imperfections at the surface act as traps that reabsorb the light before it can escape.

Postdoc Haiding Sun and his KAUST colleagues, including his supervisor, Assistant Prof. Xiaohang Li, Prof. Boon Ooi and Assistant Prof. Iman Roqan, have developed LEDs that are made up of a tight array of dislocation-free nanometer-scale aluminum-gallium-nitride nanowires on a titanium-coated silicon substrate. More light can be efficiently extracted due to the presence of the air gaps between nanowires via scattering. The trade-off however is that arrays of nanowires have a larger surface area than a planar structure. "Because of the large surface-to-volume ratio of nanowires, their optical and electrical properties are highly sensitive to their surroundings," says Sun. "Surface states and defects will lead to low-efficiency light-emitting devices."

Sun and the team show that treating the nanowires in a diluted potassium-hydroxide solution can suppress the surface reabsorption by removing dangling chemical bonds and preventing oxidization. Their results showed that a 30 second treatment led to a 49.7 percent enhancement in the ultraviolet light output power as compared with an untreated device.

"We aim to improve our device's performance in several ways," says Sun. "For example, we will optimize the nanowire growth conditions, we will use quantum-well structures in the active region and we will use different metal substrates to improve the light-extraction efficiency."
-end-


King Abdullah University of Science & Technology (KAUST)

Related Nanowires Articles from Brightsurf:

A new, highly sensitive chemical sensor uses protein nanowires
Writing in NanoResearch, a team at UMass Amherst reports that they have developed bioelectronic ammonia gas sensors that are among the most sensitive ever made.

Giving nanowires a DNA-like twist
Argonne National Laboratory played a critical role in the discovery of a DNA-like twisted crystal structure created with a germanium sulfide nanowire, also known as a 'van der Waals material.' Researchers can tailor these nanowires in many different ways -- twist periods from two to twenty micrometers, lengths up to hundreds of micrometers, and radial dimensions from several hundred nanometers to about ten micrometers.

Shell increases versatility of nanowires
Nanowires promise to make LEDs more colorful and solar cells more efficient, in addition to speeding up computers.

Scientists synthesize new nanowires to improve high-speed communication
Scientists from the Institute of Process Engineering, City University of Hong Kong and their collaborators synthesized highly crystalline ternary In0.28Ga0.72Sb nanowires to demonstrate high carrier mobility and fast IR response.

Dose of vitamin C helps gold nanowires grow
Rice University scientists discover a method to turn stubby gold nanorods into gold nanowires of impressive length.

Silver nanowires promise more comfortable smart textiles
In a paper to be published in the forthcoming issue in NANO, researchers from the Nanjing University of Posts and Telecommunications have developed a simple, scalable and low-cost capillary-driven self-assembly method to prepare flexible and stretchable conductive fibers that have applications in wearable electronics and smart fabrics.

Artificial synapses made from nanowires
Scientists from J├╝lich together with colleagues from Aachen and Turin have produced a memristive element made from nanowires that functions in much the same way as a biological nerve cell.

Nanowires could make lithium ion batteries safer
From cell phones and laptops to electric vehicles, lithium-ion batteries are the power source that fuels everyday life.

Scientists have a new way to gauge the growth of nanowires
In a new study, researchers from the US Department of Energy's Argonne and Brookhaven National Laboratories observed the formation of two kinds of defects in individual nanowires, which are smaller in diameter than a human hair.

Cleaning nanowires to get out more light
A simple chemical surface treatment improves the performance of nanowire ultraviolet light-emitting diodes.

Read More: Nanowires News and Nanowires Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.