Ab Initio Study of Coupling between Electronic and Phononic Contribution to Stress-Dependent Thermal Conductivity of Au, Si, and SiC

Abstract

This work presents an understanding of strain-thermal conductivity correlation in a metal (Au), in a semiconductor (Si), and in a ceramic (SiC) using ab initio density functional theory and utilizing a modified nonequilibrium Green's function (NEGF) approach. Separately, electronic and phononic contributions to thermal conductivity values are calculated as a function of applied tensile strain and temperature. Analyses show that electron thermal conductivity shows a significant decrease with increase in Fermi gap (metal to semiconductor to ceramic). The electronic thermal conduction has less than 5% contribution to overall thermal conductivity in the case of Si and SiC with the value being of the same order as phononic thermal conductivity in the case of Au. Phonons are dominant carriers of heat transport in Si and SiC, with such contribution reducing with increase in temperature and increase in strain. Similar reduction is observed in the case of electronic thermal conduction in Si and SiC. In the case of Au, such contribution increases only with temperature increase. Electronic contribution being at frequencies approximately three orders of magnitude higher (timescale of femtoseconds) than the phononic contribution (timescale of picoseconds) is a significant part of metallic thermal conduction. However, electronic thermal conduction in Au does not show a significant dependence on deformation, indicating that the deformation coupling may only be important in semiconductors and ceramics. The analyses here present scenario in which one must consider electronic thermal conductivity contributions while analyzing mechanical deformation. © 2012 American Society of Civil Engineers.