Valley polarization dynamics of photoinjected carriers at the band edge in room-temperature silicon studied by terahertz polarimetry

TL;DR

This study investigates the dynamics of valley polarization in silicon at room temperature using terahertz polarimetry, revealing electron valley relaxation times exceeding 1.5 ps, which supports silicon's potential for valleytronics applications.

Contribution

The paper demonstrates room-temperature valley polarization dynamics in silicon using optical pump-THz probe spectroscopy, providing experimental evidence for electron valley relaxation times and advancing silicon-based valleytronics.

Findings

Electron valley relaxation time exceeds 1.5 ps at room temperature.

Valley polarization can be probed via polarization rotation of THz pulses.

Good agreement with theoretical intervalley phonon scattering models.

Abstract

Sixfold-degenerate valleys in Si have attracted considerable attention for valleytronics application. Using optical pump-terahertz (THz) probe spectroscopy, we study the dynamics of valley polarization in bulk Si(001) at room temperature. Linearly polarized pump pulses excite electrons and holes with asymmetric distributions in momentum space, leading to in-plane anisotropic conductivity. By varying the polarization directions of the pump light relative to the in-plane crystalline axes, the valley polarization of electrons and the momentum asymmetry of holes are separately probed through observing the polarization rotation of THz pulses. We demonstrate that the valley relaxation time of electrons near the conduction band minimum exceeds 1.5 ps at room temperature, in good agreement with theoretically calculated intervalley phonon scattering with f process. This work paves the way for Si-based room-temperature valleytronics.