Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Scientists demonstrate effect of confining dielectrics on semiconductor nanowire conductivity

07.05.2009
Finding has potential to optimize the performance of nanowire electronic and optoelectronic devices

Researchers at the Harvard School of Engineering and Applied Sciences (SEAS), in collaboration with researchers from Worcester Polytechnic Institute (WPI), have demonstrated, for the first time, that the activation energy of impurities in semiconductor nanowires is affected by the surrounding dielectric and can be modified by the choice of the nanowire embedding medium.

The finding, published in the April 6 issue of Applied Physics Letters, helps to confirm the "dielectric confinement effect", a key phenomenon in doping and conduction in nanostructures proposed by L. V. Keldysh in 1979. The dielectric confinement effect influences conductivity by changing the activation energy of dopants. Understanding the phenomenon has implications for improving the design of semiconductor nanowires as electronic devices, such as in the case of gas or liquid substance detectors.

"The demonstrated effect sets in as circuit dimensions shrink, which makes the material more sensitive to external conditions," explains lead author Venkatesh Narayanamurti, John A. and Elizabeth S. Armstrong Professor of Engineering and Applied Sciences and Professor of Physics.

Surfaces act like partial mirrors reflecting inner charges, and thus, an image charge in the mirror affects the energy of the real charge. When the surface is far, the mirror image is far and its influence is negligible. But as structures enter the nanometer scale the mirror draws in, making it possible to manipulate the conduction from the outside.

In the experiments, co-author Joonah Yoon, a graduate student at SEAS, coated GaN nanowires with silicon oxide to modify the strength of the surface mirror. The dopant activation energies were obtained from the temperature dependence of the nanowire conductivity. The dominant term of the activation energies extracted out of the data was found to vary inversely with the radii of the nanowires, confirming a previous theoretical prediction.

Further, detailed calculations using finite element method, carried out by graduate student Alexi Girgis of WPI, were used to iteratively solve the wave functions and energies of conduction electrons and accounted for the induced surface charges. The inverse radius dependence turned out to be a good approximation only for certain range of wire sizes.

"Our key finding was that devices made with nanowires, such as nanowire field-effect transistors, require imaginative design of the materials, the surrounding dielectric, and the operating voltage bias to take into account dielectric confinement effects," says Narayanamurti.

Previously, the effects of dielectric confinement have been investigated theoretically for the role they play in defining the optical properties of nanostructures, such as exciton binding energies, while the impact on electrical characteristics has largely been neglected partly due to the misconception that the relevant length scale still falls into the "classical" regime.

The present work opens up the general prospect of dielectric confinement engineering, or a way to exploit and optimize the performance of nanowire electronic and optoelectronic devices.

Additional co-authors included Ilan Shalish, former Research Associate in the Narayanamurti group at SEAS and presently a faculty member at Electrical and Computer Engineering Department at Ben Gurion University in Israel and L. Ramdas Ram-Mohan, Professor of Physics and Electrical and Computer Engineering at WPI. The authors acknowledge the support of the NSF funded Nanoscale Science and Engineering Center (NSEC) at Harvard, and the Center for Computational Nanoscience at WPI.

Michael Patrick Rutter | EurekAlert!
Further information:
http://www.harvard.edu

More articles from Physics and Astronomy:

nachricht A 100-year-old physics problem has been solved at EPFL
23.06.2017 | Ecole Polytechnique Fédérale de Lausanne

nachricht Quantum thermometer or optical refrigerator?
23.06.2017 | National Institute of Standards and Technology (NIST)

All articles from Physics and Astronomy >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Can we see monkeys from space? Emerging technologies to map biodiversity

An international team of scientists has proposed a new multi-disciplinary approach in which an array of new technologies will allow us to map biodiversity and the risks that wildlife is facing at the scale of whole landscapes. The findings are published in Nature Ecology and Evolution. This international research is led by the Kunming Institute of Zoology from China, University of East Anglia, University of Leicester and the Leibniz Institute for Zoo and Wildlife Research.

Using a combination of satellite and ground data, the team proposes that it is now possible to map biodiversity with an accuracy that has not been previously...

Im Focus: Climate satellite: Tracking methane with robust laser technology

Heatwaves in the Arctic, longer periods of vegetation in Europe, severe floods in West Africa – starting in 2021, scientists want to explore the emissions of the greenhouse gas methane with the German-French satellite MERLIN. This is made possible by a new robust laser system of the Fraunhofer Institute for Laser Technology ILT in Aachen, which achieves unprecedented measurement accuracy.

Methane is primarily the result of the decomposition of organic matter. The gas has a 25 times greater warming potential than carbon dioxide, but is not as...

Im Focus: How protons move through a fuel cell

Hydrogen is regarded as the energy source of the future: It is produced with solar power and can be used to generate heat and electricity in fuel cells. Empa researchers have now succeeded in decoding the movement of hydrogen ions in crystals – a key step towards more efficient energy conversion in the hydrogen industry of tomorrow.

As charge carriers, electrons and ions play the leading role in electrochemical energy storage devices and converters such as batteries and fuel cells. Proton...

Im Focus: A unique data centre for cosmological simulations

Scientists from the Excellence Cluster Universe at the Ludwig-Maximilians-Universität Munich have establised "Cosmowebportal", a unique data centre for cosmological simulations located at the Leibniz Supercomputing Centre (LRZ) of the Bavarian Academy of Sciences. The complete results of a series of large hydrodynamical cosmological simulations are available, with data volumes typically exceeding several hundred terabytes. Scientists worldwide can interactively explore these complex simulations via a web interface and directly access the results.

With current telescopes, scientists can observe our Universe’s galaxies and galaxy clusters and their distribution along an invisible cosmic web. From the...

Im Focus: Scientists develop molecular thermometer for contactless measurement using infrared light

Temperature measurements possible even on the smallest scale / Molecular ruby for use in material sciences, biology, and medicine

Chemists at Johannes Gutenberg University Mainz (JGU) in cooperation with researchers of the German Federal Institute for Materials Research and Testing (BAM)...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Plants are networkers

19.06.2017 | Event News

Digital Survival Training for Executives

13.06.2017 | Event News

Global Learning Council Summit 2017

13.06.2017 | Event News

 
Latest News

New 3-D model predicts best planting practices for farmers

26.06.2017 | Agricultural and Forestry Science

New research reveals impact of seismic surveys on zooplankton

26.06.2017 | Life Sciences

Correct connections are crucial

26.06.2017 | Health and Medicine

VideoLinks
B2B-VideoLinks
More VideoLinks >>>