Measuring how strain affects semiconductors may pave way for faster electronics

Washington, November 4 : Researchers at the University of Wisconsin-Madison have come up with a way to measure how strain affects thin films of silicon, which they say may pave the way for faster flexible electronics.

Research leader Max Lagally, the Erwin W. Mueller and Bascom Professor of Materials Science and Engineering, highlights the fact that scientists have long known that inducing strain into the silicon, the industry standard semiconductor for electronic devices, increases the speed of such devices, but they have not fully understood why this happens.

The researcher insists that the new approach can enable scientists to directly measure the effects of strain on the electronic structure of silicon.

Standard strained silicon has so many dislocations and defects that strain measurements are not accurate, which is why the researchers start with their own specially fabricated silicon nanomembranes.

They can induce uniform strain in these extremely thin, flexible silicon sheets.

"Imagine if you were to attach a ring and a hook on all four corners and pull equally on all four corners like a trampoline, it stretches out like that," says Lagally.

All that enables the researchers to avoid the defects and variations that make it difficult to study standard strained silicon. Uniform strain allows accurate measurement of its effect on electronic properties.

For their study, the researchers drew on the powerful X-ray source at the UW-Madison Synchrotron Radiation Center (SRC), which helped measure conduction bands in strained silicon.

The group required a wavelength-tunable X-ray source to study the energy levels, and thus they used a monochromator that helped them choose a precise wavelength, giving their readings the required high-energy resolution.

Measuring nanomembranes with different percentages of strain, in turn, enabled the team to determine the direction and magnitude of shifts in the conduction bands.

Lagally says that the study shed light on divergent theories and uncovered some surprising properties. Understanding these properties and the energy shifts in strained materials, according to the researcher, could lead to the improvement of fast, flexible electronic devices.

The researchers hope to use their techniques to study strain in other semiconductor materials, as well as to make measurements over smaller areas to study the effects of localized strain, as part of their future research projects.

"The ability to make membranes of various materials, to strain them, and make these measurements will enable us to determine strain-dependent band structure of all kinds of semiconductor materials," says Lagally.

The group's findings have been published in the online edition of Physical Review Letters, and will soon appear in the print edition of the journal.

ANI