Thermopower of a 2D Electron Gas in SuspendedAlGaAs/GaAs Heterostructures

We present thermopower measurements on a high electron mobility two-dimensional electron gas (2DEG) in a thin suspended membrane. We show that the small dimension of the membrane substantially reduces the thermal conductivity compared with bulk material so that it is possible to establish a strong thermal gradient along the 2DEG even over a distance of a few micrometers. We find that the zero-field thermopower is significantly affected by the micropatterning. In contrast to 2DEGs incorporated in a bulk material, the diffusion contribution to the thermopower remains dominant up to temperature of 7?K, until the phonon drag becomes strong and governs the thermopower. We also find that the coupling between electrons and phonons in the phonon-drag regime is due to screened deformation potentials, in contrast to the piezoelectric coupling found for bulk phonons.