Effect of electron-phonon coupling on the thermoelectric efficiency of single-quantum-dot devices

The thermoelectric properties of single-quantum-dot (QD) devices have been studied theoretically taking into account the electron-phonon coupling in the QD. The thermoelectric transport coefficients and the thermoelectric efficiency have been calculated in the sequential tunneling regime. It is shown that the thermoelectric properties depend on temperature and on intrinsic properties of the QD: the electron energy spectrum, the phonon energy, and the electron-phonon coupling strength. Different regimes have been identified. In the weak electron-phonon coupling regime, it is explicitly shown that the interplay between quantum confinement and electron-phonon coupling determines the electron thermal conductance and the thermoelectric efficiency of the device. The figure of merit ZT decreases rapidly with increasing temperature and electron-phonon coupling strength. When the electron-phonon coupling is strong, it becomes evident that the thermoelectric coefficients and the thermoelectric efficiency depend primarily on phonons.