Abstract
Ultrafast optical reflectivity measurements of silicon, germanium, and gallium arsenide have been carried out using an advanced set-up providing intense subpicosecond pulses (35 fs FWHM, lambda = 400 nm) as a pump and broadband 340–780 nm ultrafast pulses as a white supercontinuum probe. Measurements have been performed for selected pump fluence conditions below the damage thresholds, that were carefully characterized. The obtained fluence damage thresholds are 30, 20.8, 9.6 mJ/hbox {cm}^2 for Si, Ge and GaAs respectively. Ultrafast reflectivity patterns show clear differences in the Si, Ge, and GaAs trends both for the wavelength and time dependences. Important changes were observed near the wavelength regions corresponding to the E_1, E_1+Delta singularities in the joint density of states, so related to the peculiar band structure of the three systems. For Ge, ultrafast reflectivity spectra were also collected at low temperature (down to 80 K) showing a shift of the characteristic doublet peak around 2.23 eV and a reduction of the recovery times.
Highlights
Ultrafast optical reflectivity measurements of silicon, germanium, and gallium arsenide have been carried out using an advanced set-up providing intense subpicosecond pulses (35 fs FWHM, = 400 nm) as a pump and broadband 340–780 nm ultrafast pulses as a white supercontinuum probe
Ultrafast optical measurements of the carrier dynamics can lead to deeper understanding of the fundamental mechanisms of the excitation and relaxation phenomena at typical 10−14 to 10−9 seconds time scales
New ultrafast optical reflectivity experiments on silicon, germanium and gallium arsenide singlecrystals have been presented in this work
Summary
We present a set of ultrafast pump–probe reflectivity experiments on Si, Ge and GaAs bulk single-crystals at selected pump fluences (pump wavelength 400 nm) coupled with a broadband optical probe, for typical 0–300 ps delay times between pump and probe pulses. To the best of our knowledge, there are no previous pump–probe reflectivity works on germanium, but time-resolved dielectric function data in the visible range[21] and models for the interpretation have been proposed[22,23] All those previous studies on Si, Ge, GaAs have been performed generally using different pump and probe wavelengths, pulsewidths, fluences, so a general picture of their ultrafast properties under conditions similar to the present work is still lacking. Measurements were extended at low temperatures for Ge (80, 150 K) where we expect distinct variations of the reflectivity features
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