Relativistic Doppler reflection as a probe for the initial relaxation of a non-equilibrium electron-hole plasma in silicon

19th International Conference on Electron Dynamics in Semiconductors, Optoelectronics and Nanostructures

Thomson, Mark D.^1 ; Meng, Fanqi^1 ; Sernelius, Bo E.^2 ; Roskos, Hartmut G.^1

Physikalisches Institut, Goethe-University, Frankfurt am Main

D-60438, Germany^1

Department of Physics, Chemistry and Biology, Linköping University, Linköping

58183, Sweden^2

关键词: Broadband terahertz pulse;    Carrier relaxation;    Counterpropagating;    Energy relaxation;    Equilibrium value;    Low carrier density;    Non-equilibrium electrons;    Pump-probe delays;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/647/1/012016/pdf
DOI  :  10.1088/1742-6596/647/1/012016

来源: IOP

【 摘 要 】

This paper reviews the status of investigations of the relativistic Doppler reflection of a broadband terahertz pulse at a counter-propagating plasma front of photo-excited charge carriers in undoped silicon. When a THz pulse with 20-THz bandwidth impinges onto a moving plasma front with a carrier density in the range of 1019per cm3, one observes a spectral up-shift, which is, however, much less pronounced than expected from simulations assuming a Drude plasma characterized by a single carrier relaxation time τ of the order of 15-100 fs. Qualitative agreement between simulations and experiments can be achieved if τ is chosen to be less than 5 fs. In order to explore carrier relaxation in more detail, optical-pump/THz-probe experiments in the conventional co-propagation geometry were performed. If the pump-probe delay is long enough for monitoring of the equilibrium value of the scattering time, τ ranges from 200 fs at low carrier density to 20 fs in the 1019-cm-3density range. For small (sub-picosecond) pump-probe delay, the data reveal a significantly faster scattering, which slows down during energy relaxation of the charge carriers.