Ultrafast long-distance expansion of electron-hole plasma in direct bandgap semiconductors

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Transport of charge carriers inside crystals is determined by their energy band structure which only permits velocities smaller than ~c/100 in known materials. We demonstrated that ultrafast and long-distance propagation of electron-hole plasma (velocities up to c/10, reaching more than 100 μm) is possible as a quite general result of fundamental electron-photon interaction in direct bandgap semiconductors upon strong pulse photoexcitation with low photon excess energy above the bandgap.

Propagation of electron-hole plasma in GaAs.
Description
Propagation of plasma as measured by THz pulse probing of photocarriers in GaAs shows that assistance of light can dramatically enhance the charge propagation rates.
(1) In incoherent regime the plasma propagation is due to stimulated emission and reabsorption of photons; (2) In coherent regime at low temperature the electron – photon interaction leads to Rabi dynamics and soliton formation and propagation; (3) for comparison: group velocity of light in GaAs.

 Contact person: Petr Kužel.