Phonon-drag effect in GaAs-Al(x)Ga(1-x)As heterostructures at very low temperatures

The thermoelectric power of high-mobility GaAs-AlxGa(l-x)As heterojunctions has been investigated in the temperature range from 0.1 to 10 K in order to study the phonon-drag effect. The phonon-drag contribution to the Seebeck coefficient can be well described by the classical T3 dependence below 2.5 K. At very low temperatures (T smaller than 0.6 K), the phonon drag becomes vanishingly small and a linear temperature dependence of the diffusion thermoelectric power was resolved. In addition, the thermoelectric power was measured in magnetic fields up to 7 T and different temperature dependences were found for the maxima of the thermoelectric power oscillations at different Landau levels. (IAF)