Phonon-drag thermopower and weak localization

Previous experimental work on a two-dimensional (2D) electron gas in a Si-o n-sapphire device led to the conclusion that both conductivity and phonon d rag thermopower S-g are affected to the same relative extent by weak locali zation. The present paper presents further experimental and theoretical res ults on these transport coefficients for two very low-mobility 2D electron gases in delta-doped GaAs/Ga(x)A(1-x) As quantum wells. The experiments wer e carried out in the temperature range 3-7 K, where phonon drag dominates t he thermopower and, in contrast to the previous work, the changes observed in the thermopower due to weak localization were found to be an order of ma gnitude less than those in the conductivity. A theoretical framework for ph onon drag thermopower in 2D and 3D semiconductors is presented that account s for this insensitivity of Sg to weak localization. It also provides trans parent physical explanations of many previous experimental and theoretical results. [S0163-1829(98)01144-8].