Atomic defects in semiconductors can now be detected using ultrafast lasers

Physicists at Michigan State University (MSU) have developed a new method for analyzing semiconductors at the atomic level. This approach combines high-resolution microscopy with ultrafast lasers to detect semiconductor “defects” like never before.

Led by Tyler Cocker, the Jerry Cowen Endowed Chair in Experimental Physics at MSU, this research aims to overcome a long-standing challenge. The need for instruments capable of probing the constituent materials of devices has become critical as instruments become smaller and more powerful.

“This is particularly relevant for components with nanoscale structures,” Cocker explained. The importance of this technique extends to cutting-edge developments in semiconductor technology, including computer chips with nanoscale features and materials engineered to be just a single atom thick.

Discovery of nuclear 'pits'

The new method detects silicon atoms intentionally mixed into gallium arsenide, which is important in radar systems, high-efficiency solar cells and modern telecommunications equipment. These silicon “defects” play a key role in tuning the speed of electrons through semiconductors.

Although theoretical physicists have studied this type of defect for decades, experimental detection of individual atoms has remained difficult until now. “The silicon atom basically looks like a deep pit for electrons,” Cocker explained.

The MSU team used a scanning tunneling microscope (STM) coupled with laser pulses at terahertz frequencies. These pulses “move up and down” a trillion times per second, resulting in a combination that creates a probe sensitive to defects.

When the STM tip encounters a silicon defect on the gallium arsenide surface, it produces a distinct, intense signal in the measurement data. Moving the tip just one atom away makes the signal disappear.

“This was the flaw people had been looking for for forty years, and we could see it ringing like a bell,” Cocker said, highlighting the importance of his observations.

Implications for the future

As semiconductor devices continue to shrink, understanding and controlling defects at the atomic level is becoming critical to performance and stability.

Cocker's team is already using its method to investigate atomically thin materials such as graphene nanoribbons. “We have a number of open projects where we're using the technique with more materials and more exotic materials,” he said.

“We’re basically incorporating it into everything we do and using it as a standard technique.”

This approach is relatively simple and versatile, making it an attractive tool for researchers around the world. Furthermore, other groups combining STM and terahertz light in different ways greatly expand the potential for more discoveries in a variety of materials.

“It's really helpful when you discover something like this, because there's already decades of theoretical research about it,” said Vedran Jelic, first author of the study.

This research was supported by the Office of Naval Research, the Office of Army Research, and the Air Force Office of Scientific Research. As the electronics industry continues to move toward smaller and more efficient devices, techniques like these will play a key role in shaping the future of semiconductor technology.

The team's findings were published in the journal Nature Photonics,


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Amal Jose Chacko Amal writes code on a typical business day and dreams of photographing amazing buildings and reading a book by the fire. He loves everything related to technology, whether it is consumer electronics, photography, cars, chess, football or F1.

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