Abstract
Transient reflectivity measurements at different probing wavelengths reveal detection mechanisms of coherent phonon and phonon-plasmon coupled modes of n-doped GaAs to be strongly depth-dependent due to the carrier depletion at the surface.
Highlights
Transient reflectivity measurements offer a general and sensitive approach to monitor coherent optical phonons.the mechanism of the reflectivity modulation by the coherent lattice oscillation remains hardly explored.Cho and coworkers measured the transient reflectivity response of GaAs for a few probe polarization angles with near infrared light [1,2], and attributed the detection of the LO phonon and LO phonon-‐plasmon coupled (LOPC) mode signals to the linear (Pockels) and non-‐linear (Franz-‐Keldysh) electro-‐optic effects
By analysing the probe-‐polarization-‐angle dependence of the coherent amplitudes, we demonstrate that different microscopic processes are operative in the detection of the LO and LOPC modes at different depths
We have investigated the depth-‐dependent detection mechanisms of the coherent LO and LOPC modes of n-‐GaAs in transient reflectivity measurements
Summary
Transient reflectivity measurements offer a general and sensitive approach to monitor coherent optical phonons. Cho and coworkers measured the transient reflectivity response of GaAs for a few probe polarization angles with near infrared light [1,2], and attributed the detection of the LO phonon and LO phonon-‐plasmon coupled (LOPC) mode signals to the linear (Pockels) and non-‐linear (Franz-‐Keldysh) electro-‐optic effects. Their conclusions were inconsistent, with the weak electro-‐optic effect in GaAs [3,4] and with the depth-‐dependent phonon-‐plasmon coupling in doped GaAs [4,5]. By analysing the probe-‐polarization-‐angle dependence of the coherent amplitudes, we demonstrate that different microscopic processes are operative in the detection of the LO and LOPC modes at different depths
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