<< Back to Program

Plenaries

Keynotes

Posters

TOPICS

XFEL Ultrafast

  • Thursday 4
  • 16:00
  • - 16:20
  • 1402
  • Talk # 3
  • Session # 2

From Bulk to Nanostructures: Understanding Carrier-Phonon Dynamics in Semiconductors

Begoña Abad1, Grazia Raciti1, Riccardo Dettori2, Raja Sen3, Aswathi K. Sivan1, Jose M. Sojo Gordillo1, Arianna Nigro1, Nathalie Vast4, Riccardo Rurali5, Claudio Melis2, Jelena Sjakste4, Ilaria Zardo1

  • 1- Department of Physics, University of Basel, 4056 Basel, Switzerland
  • 2- Department of Physics, University of Cagliari, CA 09042 Monserrato, Italy
  • 3- SATIE, CNRS, ENS Paris-Saclay, Universite Paris-Saclay, 91190 Gif-sur-Yvette, France
  • 4- Laboratoire des Solides Irradies, CEA/DRF/IRAMIS, Ecole Polytechnique, CNRS, Institut Polytechnique de Paris, 91128 Palaiseau, France
  • 5- Institut de Ciencia de Materials de Barcelona, ICMAB–CSIC, Campus UAB, Bellaterra, 08193, Spain

Presenting Author:

  • Grazia
  • Raciti

grazia.raciti@unibas.ch

Improving the performance of semiconductor devices requires a deep understanding of microscopic energy transfer mechanisms occurring on picosecond or even femtosecond timescales [1]. Pump-probe spectroscopy is a powerful method to investigate carrier and phonon dynamics in materials [2]. In these experiments, an ultrafast pump pulse excites the system, while a time-delayed probe pulse monitors the sample response after excitation, with a temporal resolution limited only by the laser pulse duration.

We present a pump-probe setup capable of performing both transient reflectivity (TR) and time-resolved Raman spectroscopy (TRRS), providing complementary insights into the energy flow between charge carriers and lattice. While reflectivity measurements track changes in the reflected probe intensity induced by the pump excitation, TRRS can directly probe the evolution of active Raman optical phonon modes after the pump pulse excitation.

We apply this approach to investigate energy relaxation in semiconductor systems. In bulk Germanium, we observe that the temperature, Raman frequency, and linewidth of the phonon mode show completely different decay dynamics. We attributed these differences to the thermal strain induced by the pump excitation. We also observe Brillouin oscillations, arising from the strain pulse propagating through the Ge, whose damping rate matches the one of the Raman broadening. These findings are supported by density functional theory and molecular dynamics simulations. We extend this study to Ge/SiGe quantum wells, where electron confinement modifies carrier relaxation and phonon scattering processes. Our results reveal how reduced dimensionality and interfaces affect carrier-phonon interactions.

We demonstrate that the combination of TR and TRRS techniques offers deeper insight into the different dynamic processes occurring in the material systems. This knowledge is relevant for the development of optoelectronic, thermoelectric, and quantum technologies.

References
[1] A. Othonos, “Probing ultrafast carrier and phonon dynamics in semiconductors,” Journal of Applied Physics, 1998.
[2] Maiuri et al., “Ultrafast Spectroscopy: State of the Art and Open Challenges,” J. Am. Chem. Soc., 2020.