Campus researchers publish findings on superacid semiconductor treatment

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A campus research team has discovered a method to dramatically increase the energy efficiency of semiconductors in electronics.

Its research — which began a year ago and was published in Science magazine Friday — focused on decreasing the power consumption of electronic switches and increasing the efficiency of LED optics, according to UC Berkeley doctoral student Matin Amani, a co-author of the study.

Semiconductors are the building blocks for electronics, used in computer chips, LED lights and solar panels, among other devices. Semiconducting material alternates from an insulating state to a conducting state, creating electronic switches and storing energy to release as light.

Monolayer semiconductor material is typically 0.7 nanometers thick, compared to the approximate 50,000-nanometer thickness of a single human hair. Any defect can dramatically affect a device’s performance, causing heat to be generated instead of light.

Ali Javey, the principal investigator and campus electrical engineering and computer sciences professor, said the team explored different chemical treatments to fix the defects. They looked at hundreds of molecules and measured the photoluminescence yield — the ratio of the light generated to the energy put in.

A trend emerged showing that strong, nonoxidizing acids enhanced the semiconductor’s properties. The team then began looking at superacids, which give protons to a substance but do not remove electrons.

Amani, one of the three lead authors along with visiting doctoral student Der-Hsien Lien and postdoctoral fellow Daisuke Kiriya, said the superacid patches up gaps in the semiconductor material so that a particle can travel long enough to emit energy as light.

The team treated the monolayer semiconductor MoS2 with a superacid chemical treatment, improving the photoluminescence yield from 1 percent efficiency to 100 percent efficiency, according to Javey.

“We went from material that was pretty defective to material that, in a semiconductor’s point of view, is perfect, despite the fact that is it so thin,” Javey said. “This is a major breakthrough because for any electronic device … what we care about is its performance, determined by the quality of the semiconductor.”

The team’s findings are the first step in the development of tunneling transistors, or electronic switches. This method requires defect-free materials for particles to flow from one semiconductor to another.

“Perfect materials don’t occur in nature — their research is helping to maintain a perfect material, even down to the atomic level,” said EECS postdoctoral student Tania Roy, who is unaffiliated with the research and studies tunneling transistors.

The goal of tunneling transistors — like the team’s research — is to increase energy efficiency.

“We need (tunneling transistors) for low-power, low-voltage electronics because we are all trying to save power,” Roy said.

The treatment now needs to be tested in prototypes before the new technology can be used in future devices.

Contact Amelia Mineiro at [email protected].