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

The phonon drag thermopower of a two-dimensional electron gas at a GaA s/Ga1-xAlxAs heterojunction has been strongly attenuated by growing th e sample on a heavily doped substrate and by working in the liquid He- 3 temperature range. As a consequence the diffusion thermopower domina tes at T < 0.5 K, at least at zero magnetic held. The tow-field oscill ations in the resistivity and thermopower have been investigated. The former behave essentially as predicted. The amplitude of the oscillati ons in the Nernst-Ettingshausen coefficient shows the field and temper ature dependence expected for diffusion, although the absolute magnitu de is about a factor of 2 too large. The amplitude of the longitudinal thermopower oscillations does not behave as expected for diffusion, a lthough the oscillations exhibit the predicted change in phase as a fu nction of magnetic field.