OSCILLATIONS IN THE DIFFUSION THERMOPOWER OF A 2-DIMENSIONAL ELECTRON-GAS

The phonon drag thermopower of a two-dimensional electron gas at a GaAs/Ga1-xAlxAs heterojunction has been strongly attenuated by growing the sample on a heavily doped substrate and by working in the liquid He-3 temperature range. As a consequence the diffusion thermopower dominates at T < 0.5 K, at least at zero magnetic field. The tow-field oscillations in the resistivity and thermopower have been investigated. The former behave essentially as predicted. The amplitude of the oscillations in the Nernst-Ettingshausen coefficient shows the field and temperature dependence expected for diffusion, although the absolute magnitude is about a factor of 2 too large. The amplitude of the longitudinal thermopower oscillations does not behave as expected for diffusion, although the oscillations exhibit the predicted change in phase as a function of magnetic field.