Transparent nanoscale semiconductor has highest ever conductivity

6th May 2017
Minnesota team says wide bandgap BaSnO3 film is ideal material for improving electronics and solar cells


A team of researchers, led by the University of Minnesota, has discovered a new nanoscale thin film material with the highest-ever conductivity in its class. They say the new material could lead to smaller, faster, and more powerful electronics, as well as more efficient solar cells.

The discovery is reported in Nature Communications -  'Wide Bandgap BaSnO3 Films with Room Temperature Conductivity Exceeding 104 Scm-1' 

According to the researchers, what makes this new material unique is a combination of high conductivity and wide bandgap, which means light can easily pass through making it optically transparent. In most cases, materials with wide bandgap have either low conductivity or poor transparency.

"The high conductivity and wide bandgap make this an ideal material for making optically transparent conducting films which could be used in a wide variety of electronic devices, including high power electronics, electronic displays, touchscreens and even solar cells in which light needs to pass through the device," said Bharat Jalan, a University of Minnesota chemical engineering and materials science professor and the lead researcher on the study.

Most transparent conductors in today's electronics use indium, but the price of indium has gone up tremendously in the past few years adding to the cost of display technology. 

In this study, the researchers developed their transparent conducting thin film using a novel synthesis method, in which they grew a BaSnO3 thin film (barium stannate), but replaced elemental tin source with a chemical precursor of tin.

The chemical precursor of tin has properties that enhanced the chemical reactivity and greatly improved the metal oxide formation process. Both barium and tin are significantly cheaper than indium and are abundantly available.

"We were quite surprised at how well this unconventional approach worked the very first time we used the tin chemical precursor," said University of Minnesota chemical engineering and materials science graduate student Abhinav Prakash, the first author of the paper. "It was a big risk, but it was quite a big breakthrough for us."

Jalan and Prakash said this new process allowed them to create this material with unprecedented control over thickness, composition, and defect concentration and that this process should be highly suitable for a number of other material systems where the element is hard to oxidise. The new process is also reproducible and scalable.

They further added that it was the structurally superior quality with improved defect concentration that allowed them to discover high conductivity in the material. They said the next step is to continue to reduce the defects at the atomic scale.

"Even though this material has the highest conductivity within the same materials class, there is much room for improvement in addition, to the outstanding potential for discovering new physics if we decrease the defects. That's our next goal," Jalan said.

The research was funded by the National Science Foundation (NSF), Air Force Office of Scientific Research (AFOSR), and U.S. Department of Energy.

In addition to Jalan and Prakash, the research team included Peng Xu, University of Minnesota chemical engineering and materials science graduate student; Cynthia S. Lo, Washington University assistant professor; Alireza Faghaninia, former graduate student at Washington University; Sudhanshu Shukla, researcher at Lawrence Berkeley National Laboratory and Nanyang Technological University; and Joel W. Ager III, Lawrence Berkeley National Laboratory and University of California Berkeley adjunct professor

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