Theoretical modeling of the thermoelectric figure of merit in Si/Si_1-xGex 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 recently in various systems. This work presents theoretical modeling of the thermoelectric properties in Si/Si_1-xGe_x quantum well structures. The model is based on solving the Boltzmann transport equation for both electronic and phonon transport in the in-plane direction of the quantum well. 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. Some important issues related to device applications, such as temperature dependent properties and the influence of the carrier mobility, are also discussed.