Ultrafast electrons and lasers reveal unexpectedly strong radiation signals in common semiconductors

In a groundbreaking study, Stanford University researchers collaborated with the Department of Energy's SLAC National Accelerator Laboratory to explore an unexpected phenomenon in common semiconductors. By utilizing ultrafast electrons and lasers, they discovered unexpectedly strong radiation signals that significantly deviate from what was previously observed.

This finding, published in the journal Nature Photonics, offers new insights into the behavior of materials and potentially paves the way for advanced sensing technologies.

Typically, radiation detection relies on trade-offs between signal strength and speed. Strong signals can be weak and slow to develop, while fast signals tend to be weaker. Diana Jeong, an instructor of radiology at Stanford University, aimed to investigate optical signal strengths induced by ionization across various material classes to find a better balance between these factors.

She hypothesized that ultrafast laser pulses could detect a light signal immediately following ionization, providing a potential solution to this trade-off.

The researchers employed the Megaelectronvolt Ultrafast Electron Diffraction (MeV-UED) instrument at SLAC's Linac Coherent Light Source (LCLS), a powerful electron camera capable of studying atomic and molecular dynamics. Instead of using electrons to image samples, they deposited high-energy electrons into the semiconductors to detect the resulting changes with synchronized laser pulses across different wavelengths. This unique approach allowed them to probe the optical response of materials within an ultrafast timeframe.

The team focused on II-VI semiconductors, common materials used in electronic applications such as infrared detectors and photovoltaic solar cells. These semiconductors convert high-energy radiation from electrons into measurable changes in their optical properties. The experiment revealed that the charge carriers generated from the electrons were densely packed in local pockets, rather than being evenly distributed throughout the sample.

This unexpected finding shifted the band gap of the materials, altering their ability to absorb and transmit light.

These insights could have significant implications for the development of advanced sensing technologies. The dense pockets of energy could enable the creation of new imaging systems capable of real-time disease monitoring and diagnosis. Jeong believes that similar effects would likely be observed in lower-energy systems, such as imaging tools used in physician offices.

By understanding how high-energy electrons affect materials and generate strong signals, researchers can develop innovative sensing platforms that form images immediately upon detection.