Evidence of phonon drag in the thermopower of a GaAs-Ga0.68Al0.32As heterojunction

We report the first experimental demonstration that phonon drag is present in the thermopower of a two-dimensional electron gas at a GaAs-${\mathrm{Ga}}_{0.68}$ ${\mathrm{Al}}_{0.32}$As heterojunction in both zero and high magnetic fields. The experiment involves polishing the rear surface of the GaAs plate on which the junction is grown in order to increase the phonon mean free path. This results in an increase of the thermopower by about a factor of 2 even though the electrical resistivities are unaffected.