Optimization of Electron-Phonon Coupling and Electronic Transport in Semiconductor Superlattices

Efficient thermoelectric (TE) materials require to maintain low thermal conductivity and high electronic transport properties to attain the phonon-glass-electron-crystal regime. Phonon engineering approaches in superlattices (SL) have been demonstrated to significantly hinder thermal conductivity. However, investigation of electron-phonon interaction (EPI) is a key factor to design devices with high electronic performance. In this work, we investigate electron-phonon coupling and electronic transport in Si/Ge SLs by employing first principle DFT calculations in conjunction with semi-classical Boltzmann transport theory. Computation of EPI requires fine sampling of Brillouin zone and, therefore, becomes expensive even for small systems. In order to reduce computational cost, we employ an assumption that the scattering rates are proportional to the electronic density of states (DOS). [1] We establish that the constants of proportionality linearly depend on SL period, composition and strain by rigorous computations. This relationship allows us to predict EPI rates for arbitrary Si/Ge SL and to determine the parameters to optimize electronic transport and therefore, thermoelectric performance of short period SL.
[1] JAP 122, no. 17 175102 (2017).