Energy loss rates for hot electrons and holes in GaAs quantum wells.

We report the first direct determination in a semiconductor of hot electron and hot hole energy loss rates due to collisions with phonons. The rate for electrons is found to be a factor of 25 smaller than for holes in GaAs/A1GaAs quantum wells. This large difference results from an anamalously low electron energy loss rate, which we attribute to non-equalibrium optical phonon populations rather than to reduced dimensionality or dynamic screening.