Fulbright takes researcher to Sweden to study new transistor materials

Joan Redwing at Lund University

By: Liam Jackson [Penn State News Article]

January 19, 2017

UNIVERSITY PARK, Pa. — Cell phones, laptops and other portable electronic devices rely on the semiconductor material silicon to provide computing power and speed, but that won't always be the case.

"The semiconductor industry is reaching the end of the road in terms of the performance they can get out of silicon, so they are looking at other materials that can help," said Joan Redwing, Penn State professor of materials science and engineering, chemical engineering, and electrical engineering. "There's an interest in developing transistors that can operate at lower power to reduce the battery requirements of current portable devices."

Potential replacements for silicon are III-V semiconductor nanowires made out of materials such as gallium antimonide, which Redwing spent three months researching at Lund University in Sweden, as part of the competitive Fulbright Scholar Program.

Nanowires are strands of material ranging from a few to hundreds of nanometers wide. They are formed in a controlled environment in which atoms are slowly deposited onto a base, known as a substrate, that contains small metal nanoparticles. A chemical reaction takes place that allows molecules to dissolve into the metal nanoparticle and attach themselves to one another, resulting in a crystalline nanowire. At this microscopic scale — for reference, a piece of paper is roughly 100,000 nanometers thick and DNA is only a handful of nanometers in diameter — there are many factors that affect how the nanowire grows.

Redwing, who has more than 15 years of experience researching nanowire materials in her laboratory, partnered with scientists from NanoLund, a highly regarded research center in Sweden that is similar to Penn State's Materials Research Institute. She collaborated primarily with students and scientists in the research group overseen by Lars-Erik Wernersson, professor of electrical and information technology.

"I was interested in working with a group that's very focused on making devices out of nanowires," said Redwing, who is also the director of Penn State's Materials Innovation Platform, called the 2D Crystal Consortium. "There were people at Lund who worked on growth of nanowires, people focused on device fabrication and testing, and another group looking at how to integrate devices into systems."

The team investigated what factors might lead to "point defects" during the growth of gallium antimonide nanowires.

"In these materials, you have a crystalline lattice, and all atoms are at a particular location in the lattice. A point defect would be a missing atom, or an impurity. It's a very small-scale defect," Redwing said.

They completed a series of experiments, varying conditions such as temperature and the ratio of gallium to antimony. Their ultimate goal is to use the nanowires in transistors to identify whether different concentrations and types of point defects lead to reduced device performance.

That project is ongoing at Lund University, and Redwing will continue to collaborate on interpreting the team's findings.

"It was great to experience the research and cultural environment of Sweden," she said. "I had a really good experience, and I would highly recommend that other researchers in engineering or the sciences look into the Fulbright Scholars Program."