EXPERIMENTAL AND THEORETICAL INVESTIGATION OF THE DRIFT VELOCITY AND VELOCITY DISTRIBUTION FUNCTION IN GAAS ALGAAS HETEROSTRUCTURES/

We have investigated the temperature dependence and electron concentra tion dependence of the drift velocity in AlGaAs/GaAs heterostructures for electric fields up to 2 kV cm-1. The saturation behaviour of the d rift velocity at different temperatures could be well described by ass uming LO-phonon emission as well as intersubband scattering processes. An increase of the saturation drift velocity with increasing electron concentration was found which can be explained by screening effects. All experimental data were compared with theoretical calculations base d on a Boltzmann integral as well as a balance equation method. In add ition, the electron distribution function was measured directly using the Smith-Purcell effect. We observed a clear cut-off of the distribut ion function at the LO-phonon energy and a shift to higher velocity va lues with increasing applied electric field. Distinct deviations of th e emission spectra from a drifted hot Fermi distribution were found.