Mechanism of the enhanced thermoelectric power in (111)-oriented n-type PbTe/Pb1-xEuxTe multiple quantum wells

A theoretical investigation of the recently observed enhanced thermoelectri c power S in (111)-oriented n-type PbTe/Pb1-xEuxTe multiple-quantum-wells ( x similar or equal to 0.09) has been carried out, including both longitudin al acoustic phonon deformation potential scattering and polar optical phono n scattering of the two-dimensionally confined electrons in the quantum wel ls. An enhancement in S is observed experimentally and predicted theoretica lly, despite the lifting of the conduction band valley degeneracy, and an e xcellent agreement between the experimental and theoretical results has bee n obtained over a wide temperature range(80-400 K). In the low temperature regime (similar to 100 K), the polar optical phonons are found to be more e ffective in scattering carriers in the oblique L-point valleys than in scat tering carriers in the longitudinal L-point valley, making the resulting S somewhat suppressed in this temperature regime. Tn the high temperature reg ime (greater than or equal to 300 K), the polar optical phonon scattering g enerally contributes to increasing S due to the particular shape of the dis tribution function associated with it. It is emphasized that our theoretica l model requires virtually no fitting parameters. The excellent agreement b etween the theoretical and experimental results suggests the validity of ou r model of enhanced thermoelectric figure of merit in two-dimensional struc tures and the reliability of the values of the parameters for the superlatt ice deduced from other independent measurements, such as Hall carrier conce ntrations and band energy gaps. [S0163-1829(99)07243-4].