Effect of dislocations on phonon drag thermopower in GaN/AlGaN heterojunctions

The phonon drag contribution, Sg, to the thermopower in GaN/AlGaN heterojunctions is studied, for the first time, over the temperature range 2 < T < 100 K. The two-dimensional electrons are considered to interact via screened deformation and piezoelectric potentials, whereas the phonons are assumed to be scattered by sample boundaries, impurities, dislocations and other phonons. Numerical results for Sg are presented with the intrinsic phonon parameters obtained from thermal conductivity data. Sg is found to be of the order of a few mV/K. The effect of dislocations is not only to reduce Sg but also to modify its behaviour.