Terahertz pulses used to excite phonons in semiconductor materials

Terahertz pulses used to excite phonons in semiconductor materials
by Riko Seibo
Tokyo, Japan (SPX) May 03, 2024

A new technique using terahertz frequency lasers has shown promising results in inducing atomic excitation in semiconductor materials, specifically in two-dimensional transition metal dichalcogenides (TMDs). Researchers at Yokohama National University, in collaboration with the California Institute of Technology, have successfully demonstrated this process, which is critical for advancing semiconductor technology

The findings, which were highlighted in an Editor's Pick article in Applied Physics Letters, show that ultrafast broadband terahertz pulses can effectively induce coherent phonon dynamics in TMD materials. Coherent phonons are vibrations of atoms in a crystal lattice that play a key role in determining the properties of materials.

"Our study addresses the fundamental question of how coherent phonons are induced by ultrafast terahertz frequency lasers-or low-energy photons-in TMD materials," explained Satoshi Kusaba, an assistant professor at the Graduate School of Engineering Science of Yokohama National University and first author of the study.

Traditionally, coherent phonons in semiconductors are excited by ultrashort pulsed lasers in the visible to near-infrared spectrum. The novelty of this study lies in the use of terahertz radiation, which occupies the spectrum between microwaves and infrared light.

"The most important finding from our study is that terahertz excitation can induce coherent phonons in TMDs through a distinct sum-frequency excitation process," said Haw-Wei Lin, a PhD candidate at the California Institute of Technology at the time of research and co-first author of this study. "This mechanism, which is fundamentally different from resonant and linear absorption processes, involves the combined energy of two terahertz photons matching that of the phonon mode."

This breakthrough allows for precise control over the atomic motions within materials, which could be pivotal for developing new electronic devices that operate on low power consumption but with high-speed computing capabilities. The researchers are optimistic that their technique will pave the way for advancements in valleytronics and specialized light sources, using TMDs.

Research Report:Terahertz sum-frequency excitation of coherent optical phonons in the two-dimensional semiconductor WSe2