DIRECT OBSERVATION OF THE HOT-ELECTRON DISTRIBUTION FUNCTION IN GAAS ALGAAS HETEROSTRUCTURES/

A new direct experimental technique to study the form of the hot elect ron distribution function is presented. Far infrared emission induced by a weak periodic potential is observed in high-mobility GaAs/AlGaAs heterostructures with extremely low electron density. The electric-fie ld-dependent spectra give for the first time evidence of a nonequilibr ium shape of the electronic distribution in the electric field directi on. The onset of LO-phonon emission is clearly observed. Perpendicular to the applied electric field, a smooth form of the distribution is f ound. The results agree well with theoretical distribution functions o btained from the Boltzmann transport equation.