THERMOELECTRIC PROPERTIES OF A VERY-LOW-MOBILITY 2-DIMENSIONAL ELECTRON-GAS

Experimental data on the thermoelectric coefficients of a very-low-mobility (=0.13 m2/V s) two-dimensional electron gas in a GaAs/Ga1-xAlxAs quantum well are presented. The measurements span a temperature range of 1200 K, and have been made in magnetic fields up to 8 T (at which point 1). As with high-mobility samples, phonon drag is found to be dominant at low temperatures, showing that the sample mobility is not relevant to this quantity. Data on the thermopower Sxx(B) and the Nernst-Ettingshausen coefficient Syx(B) are compared with recent theoretical predictions. In the absence of magnetic field, B=0, the phonon mean free path (mfp) is initially determined from the measured thermal conductivity. Then the calculated value of Sxx(0) (thermopower in zero field) is in good agreement with measured values when T<10 K but becomes up to an order of magnitude too small when T>20 K. To avoid this problem when B 0 the phonon mfp is redetermined from the measured values of Sxx(0) with the diffusion part subtracted. Then the calculated magnetothermopower Sxx(B) is in good agreement with the data. The calculated drag contribution Syxg(B) to the Nernst-Ettingshausen coefficient Syx(B), however, is only 5.4% of that measured. When the theoretical value of the contribution to Syx(B) due to phonon drag is increased by a factor of (0.054)-1=18.5 for all B and T, very good agreement with the data is again obtained over the whole regime investigated experimentally. © 1994 The American Physical Society.