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Time-resolved terahertz spectroscopy was used to visualize propagation of electron-hole plasma in strongly photoexcited GaAs and InP. The observed unprecedented speed and distance of the plasma propagation largely exceed the so far observed transport properties of charges in semiconductors (see figure). The observed phenomena stem from fundamental interactions of electron-hole system with light and we predict that they should occur in most semiconductors with direct bandgap under suitable conditions.
Description
Temporal evolution of the electron-hole plasma after photoexcitation by an ultrashort laser pulse. The slopes of the curves correspond to the speed of plasma front (which is compared to the speed of light c).
(1) At high temperatures, the laser pulse is first absorbed (t≲0.5 ps); subsequently, hot electron-hole plasma cools down to form an inversion of population (t≲2 ps, plateau phase); finally, stimulated emission and reabsorption of photons occurs leading to the observed plasma expansion.
(2) At low temperatures, a coherent interaction leads to a soliton formation and propagation of the coupled electron-photon system at high speed.
(1) At high temperatures, the laser pulse is first absorbed (t≲0.5 ps); subsequently, hot electron-hole plasma cools down to form an inversion of population (t≲2 ps, plateau phase); finally, stimulated emission and reabsorption of photons occurs leading to the observed plasma expansion.
(2) At low temperatures, a coherent interaction leads to a soliton formation and propagation of the coupled electron-photon system at high speed.
Contact person: Petr Kužel.