Researchers at the University of Basel have taken a closer look at how energy moves through one of the most established semiconductor materials, germanium, using a combination of ultrafast measurement techniques that capture processes unfolding on trillionths of a second. The work provides a clearer, time-resolved picture of how electronic excitation translates into heat inside a solid, a question that sits at the center of modern device performance and reliability.
The Basel team, led by Professor Ilaria Zardo from the Department of Physics and the Swiss Nanoscience Institute, focused on observing these interactions directly in germanium. While germanium has been studied for decades, capturing the full energy-transfer pathway between electrons and phonons in real time has remained technically challenging. The researchers addressed this by combining time-resolved Raman spectroscopy, which tracks changes in lattice vibrations, with transient reflection spectroscopy, which monitors how the material’s optical properties evolve after excitation.
Raciti, G., Abad, B., Dettori, R., Sen, R., K. Sivan, A., Sojo‐Gordillo, J. M., Vast, N., Rurali, R., Melis, C., Sjakste, J., & Zardo, I. (2026). Unraveling Energy Flow Mechanisms in Semiconductors by Ultrafast Spectroscopy: Germanium as a Case Study. Advanced Science. https://doi.org/10.1002/advs.202515470
Semiconductors underpin almost every electronic system, from consumer devices to sensors and data infrastructure. When electrons inside these materials are excited—by light or electrical signals—they do not act alone. Their motion disturbs the crystal lattice, creating collective atomic vibrations known as phonons. These vibrations govern how energy is redistributed and ultimately dissipated as heat. Understanding this sequence in detail is essential for designing devices that operate faster, heat less, and recover more efficiently after excitation.
Professor Ilaria Zardo from University of Basel stated,
“If we imagine that the time gap between two laser pulses (which is actually 1 microsecond) lasts 10 days, then the sample’s response that we record in the semiconductor lasts just a second.”
The Basel team, led by Professor Ilaria Zardo from the Department of Physics and the Swiss Nanoscience Institute, focused on observing these interactions directly in germanium. While germanium has been studied for decades, capturing the full energy-transfer pathway between electrons and phonons in real time has remained technically challenging. The researchers addressed this by combining time-resolved Raman spectroscopy, which tracks changes in lattice vibrations, with transient reflection spectroscopy, which monitors how the material’s optical properties evolve after excitation.
Using laser pulses lasting just 30 femtoseconds, the researchers excited the germanium sample and then recorded how energy moved through the system on picosecond timescales. This approach allowed them to resolve individual steps in the transfer of energy from the electronic system into specific lattice vibrations. According to first author Dr. Grazia Raciti, the paired techniques made it possible to observe not only the presence of phonons, but also how their frequency, intensity, and lifetime changed as the material relaxed.
Capturing such processes required exceptional sensitivity and stability. Measurements ran continuously for up to 48 hours, with the material excited once every microsecond. Although the delay between pulses is relatively long, the relevant physical response occurs in a time window that is orders of magnitude shorter. As Dr. Begoña Abad Mayor, a member of the research team, explains, the experiment effectively observes events that would last a single second if a ten-day interval represented the time between laser pulses. Within this narrow window, the team detected changes smaller than one percent in signal intensity and shifts of less than 0.2 inverse centimeters in vibrational frequency.
To interpret these results, the experimental work was supported by advanced computational modeling. Simulations helped link the observed signals to specific physical mechanisms, allowing the researchers to distinguish between different pathways through which energy is redistributed and converted into heat. This combined experimental–theoretical framework strengthens confidence in the conclusions and provides a reference point for studying other semiconductor systems.
The findings contribute to a more detailed understanding of energy dissipation in crystalline semiconductors, an issue that becomes increasingly important as devices shrink and operate at higher speeds. Excess heat limits performance and lifetime, particularly in densely integrated electronics. By resolving how and how quickly energy flows from excited electrons into the lattice, the work offers insights that could inform the development of improved materials, phononic components, and thermal management strategies.
While the study focuses on germanium, the methodology itself is broadly applicable. Similar approaches could be used to examine newer semiconductor materials, including those proposed for next-generation electronics and optoelectronics. As devices continue to push physical limits, the ability to observe energy flow step by step may become a key tool in engineering materials that balance speed, efficiency, and thermal stability.
Adrian graduated with a Masters Degree (1st Class Honours) in Chemical Engineering from Chester University along with Harris. His master’s research aimed to develop a standardadised clean water oxygenation transfer procedure to test bubble diffusers that are currently used in the wastewater industry commercial market. He has also undergone placments in both US and China primarely focused within the R&D department and is an associate member of the Institute of Chemical Engineers (IChemE).
