Theoretical modeling of the thermoelectric figure of merit in Si/Si_1-xGe_x quantum well structures

In bulk form, Si_1-xGe_x is a promising thermoelectric material for high temperature applications. Evidence for the enhancement of the thermoelectric figure of merit in quantum well structures has been shown experimentally in the PbTe system. A model based on solving the Boltzmann transport equation for both the electronic and phonon transport in the in-plane direction of the quantum well is presented for thermoelectric phenomena in Si/Si_1-xGe_x quantum well multilayers. The electronic transport is based on a detailed consideration of the band structure of Si and Si_1-xGe_x in the presence of quantum confinement, and the phonon transport is solved by assuming that the interfaces reflect and transmit phonons on a partially diffuse and partially specular basis. It is shown that significant enhancement of the thermoelectric figure of merit in quantum well structures can be achieved in such a system. The temperature dependent transport properties are also discussed.