Femtosecond Carrier Thermalization in Dense Fermi Seas

Abstract

We study the effects of excess thermalized electron and hole populations on femtosecond carrier thermalization in optically excited GaAs quantum wells. In modulation-doped samples we find that the presence of 3\ifmmode\times\else\texttimes\fi{}${10}^{11}$ ${\mathrm{cm}}^{\ensuremath{-}2}$ electrons produces an extraordinarily fast carrier thermalization (faster than 10 fs); however, the presence of the same density of holes yields a thermalization time close to that of undoped samples (\ensuremath{\cong}60 fs). These results give the first direct evidence that electron-electron interactions yield the dominant contributions to carrier thermalization in GaAs and also show that the electron distribution function itself influences thermalization dynamics.