MMaterialsgateNEWS 2017/07/05

Related MaterialsgateCARDS

Keeping the heat out

Insights into the thermal behavior of metal nitride nanowires could open new avenues in optical electronics.

Most electronic devices currently contain silicon-based chips. Other semiconducting materials show potential, but need further research to become commercially viable. Researchers at KAUST have thoroughly analyzed one such material—metal-nitride nanowires—bringing them a step closer to being useful.

When metal-nitride semiconductors are arranged into nano-sized wires they become extra sensitive to light, opening possibilities for optical electronics. One notable challenge however is that although metal-nitride nanowires perform well at low temperatures, thermal effects can greatly affect their performance at room temperature. To address this problem, Nasir Alfaraj with his Ph.D. supervisor Xiaohang Li and coworkers at KAUST have produced the most detailed study yet of these thermal effects1.

The researchers prepared gallium-nitride (GaN)-based nanowires in a p-i-n structure—a sandwich with layers of so-called p-type and n-type versions of the semiconductor surrounding an unaltered layer. N-type semiconductors are doped with materials that provide extra electrons, while p-types are doped with materials with fewer electrons, leaving “holes” in the crystal structure. Both electrons and holes act as charge carriers, giving semiconductor devices their useful electronic properties.

“GaN-based p-i-n nanowires are suitable for fabricating signal attenuators, high-frequency digital switches and high-performance photodetectors,” said Alfaraj. “Yet, their performance is negatively affected when electrons and holes recombine, especially close to room temperature.”

More specifically, when an electric field acts across a nanowire, the balance of electrons and holes can be affected, pumping heat away from the device in the form of thermal radiation. The devices effectively act as mini refrigerators, and their performance declines as they cool.

To quantify this effect, Alfaraj and co-workers directed a titanium-sapphire laser onto their nanowires and measured the photoluminescent emissions that came out of the sample. They were then able to calculate the “photoinduced entropy” of the system: a thermodynamic quantity that represents the unavailability of a system's energy for conversion into work due to luminescence refrigeration.

At system temperatures above 250 K, the electron-hole nonradiative recombination processes become dominant–electrons fall into holes, causing a rise in photoinduced entropy and reducing the device performance.

“We plan to investigate photoinduced entropy in other materials, such as aluminum-gallium-nitride and zinc-oxide nanowires,” said Alfaraj. “We will also compare different nanowire diameters and investigate other structures, such as thin films.”

These studies will assist engineers in making metal-nitride nanowire devices that are thermally stable and suitable for everyday use.

Source: King Abdullah University of Science & Technology (KAUST) – 02.07.2017.

Investigated and edited by:

Dr.-Ing. Christoph Konetschny, Inhaber und Gründer von Materialsgate
Büro für Material- und Technologieberatung
The investigation and editing of this document was performed with best care and attention.
For the accuracy, validity, availability and applicability of the given information, we take no liability.
Please discuss the suitability concerning your specific application with the experts of the named company or organization.

You want additional material or technology investigations concerning this subject?

Materialsgate is leading in material consulting and material investigation.
Feel free to use our established consulting services

MMore on this topic

Credit: Rob Felt, Georgia Tech

A simple technique for producing oxide nanowires directly from bulk materials could dramatically lower the cost of producing the one-dimensional (1D) nanostructures.

That could open the door for a broad range of uses in lightweight structural composites, advanced sensors, electronic devices - and thermally-stable and strong battery membranes able to withstand temperatures of more than 1,000 degrees Celsius. The technique uses a solvent reaction with a bimetallic alloy - in which one of the metals is reactive - to form bundles of nanowires (nanofibers) upon reactive metal dissolution. The process is conducted at ambient temperature and pressure without the use of catalysts, toxic chemicals or costly processes such as chemical vapor deposition. The produced nanowires can be used to improve the electrical, thermal and mechanical properties of functional... more read more

Researchers from Brown University and North Carolina State University have found that nanowires made of zinc oxide are highly anelastic, meaning they return to shape slowly after being bent, rather that snapping right back.

The findings, published in the journal Nature Nantechnology, add one more to the growing list of interesting properties found in nanoscale wires, tiny strands thousands of times thinner than a human hair. "What's surprising here is the magnitude of the effect," said Huajian Gao, the Walter H. Annenberg Professor of Engineering and a coauthor of a new paper describing the research. "Anelasticity is present but negligible in many macroscale materials, but becomes prominent at the nanoscale. We show an anelastic effect in nanowires that is four orders of magnitude larger than what is observed in even the most anelastic bulk materials." The findings are significant... more read more

The latest research from the Niels Bohr Institute shows that LEDs made from nanowires will use less energy and provide better light.

The researchers studied nanowires using X-ray microscopy and with this method they can pinpoint exactly how the nanowire should be designed to give the best properties. The results are published in the scientific journal, ACS Nano. Nanowires are very small - about 2 micrometers high (1 micrometer is a thousandth of a millimetre) and 10-500 nanometers in diameter (1 nanometer is a thousandth of a micrometer). Nanowires for LEDs are made up of an inner core of gallium nitride (GaN) and a layer of indium-gallium-nitride (InGaN) on the outside, both of which are semiconducting materials. "The light in such a diode is dependent on the mechanical strain that exists between the two materials... more read more

Berkeley Lab team shows metal-alloy catalysts give more control in nanowire fabrication.

A novel approach to growing nanowires promises a new means of control over their light-emitting and electronic properties. In a recent issue of Nano Letters, scientists from the U.S. Department of Energy's Lawrence Berkeley National Lab (Berkeley Lab) demonstrated a new growth technique that uses specially engineered catalysts. These catalysts, which are precursors to growing the nanowires, have given scientists more options than ever in turning the color of light-emitting nanowires. The new approach could potentially be applied to a variety of materials and be used for making next-generation devices such as solar cells, light emitting diodes, high power electronics and more, says Shaul... more read more

MaterialsgateNEWSLETTER

Partner of the Week

Search in MaterialsgateNEWS

Books and products

MaterialsgateFAIR:
LET YOURSELF BE INSPIRED