news digest ♦ Power Electronics
However, the researchers say that calculations for piezoelectricity of GaN nanowires as a function of size were carried out in this work for the first time, and the results are clearly more promising as GaN shows a more prominent increase.
“Our calculations reveal that the increase in piezoelectric coefficient is a result of the redistribution of electrons in the nanowire surface, which leads to an increase in the strain-dependent polarisation with respect to the bulk materials,” Espinosa said.
The findings may have important implications in the field of energy harvesting as well as for fundamental science.
For energy harvesting, where piezoelectric elements are used to convert mechanical energy to electrical energy to power electronic devices, these results point to a reduction in size of the piezoelectric elements down to the nanometre scale. Energy harvesting devices built from small- diameter nanowires should in principle be able to produce more electrical energy from the same amount of mechanical energy than their bulk counterparts.
In terms of fundamental science, these results support previous conclusions that are important on the nanoscale scale. The scientists say that by tailoring the size of nanostructures, their mechanical, electrical and thermal properties can be tuned as well.
“Our focus remains on understanding the fundamental principles governing the behaviour of nanostructures as a function of their size,” say the researchers. “One of the most important issues that needs to be addressed is to obtain experimental confirmation of these results, and establish up to what size the giant piezoelectric effects remain significant.”
Espinosa and Agrawal hope their work will spur new interest in the electromechanical properties of nanostructures, both from theoretical and experimental standpoints, in order to clear the path for the design and optimisation of future nanoscale devices.
If you want to find out more about this research, see the paper, “Giant Piezoelectric Size Effects
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www.compoundsemiconductor.net January / February 2011
in Zinc Oxide and Gallium Nitride Nanowires. A First Principles Investigation” by Ravi Agrawal and Horacio D. Espinosa published online in Nano Letters on January 11, 2011(DOI: 10.1021/ nl104004d).
Cree Launches Industry’s First Commercial SiC Power MOSFET
Destined to replace silicon in high voltage (≥ 1200V) power electronic devices, Cree’s CMF20120D delivers 1200V blocking voltage and is claimed to have the lowest switching losses in its class.
Cree, a major supplier of LEDs, has introduced what it claims is the industry’s first fully-qualified commercial silicon carbide power MOSFET.
The firm says the device establishes a new benchmark for energy efficient power switches and can enable design engineers to develop high voltage circuits with extremely fast switching speeds and ultralow switching losses.
The SiC MOSFET can be used today for solar inverters, high-voltage power supplies and power conditioning in many industrial power applications. Over the next several years, SiC power switches and diodes could also expand into motor drive control, electric vehicles and wind energy applications. The market for power semiconductors in these applications is estimated at approximately $4 billion today, reaching nearly $6 billion by 2015.
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