Effect of strain on the thermoelectric properties of silicon: An ab initio study

TL;DR

This study uses first-principles calculations to explore how biaxial strain affects the thermoelectric properties of silicon, revealing potential enhancements in powerfactor under specific doping and temperature conditions.

Contribution

It provides a detailed analysis of strain effects on silicon's thermoelectric properties and introduces an analytical model to explain band-structure related phenomena.

Findings

Powerfactor enhancement in low-temperature, low-doping regimes for certain strains.

Slight powerfactor increase in high-temperature, high-doping regimes for hole-doped silicon under tensile strain.

Band-structure effects explain the decrease in thermopower due to strain-induced band lifting.

Abstract

On the basis of detailed first-principles calculations the anisotropic thermoelectric transport properties of biaxially strained silicon were studied with focus on a possible enhancement of the powerfactor. Electron as well as hole doping were examined in a broad doping and temperature range. In the low-temperature and low-doping regime an enhancement of the powerfactor was obtained for compressive and tensile strain in the electron-doped case and for compressive strain in the hole-doped case. In the thermoelectrically more important high-temperature and high- doping regime a slight enhancement of the powerfactor was only found for the hole-doped case under small biaxial tensile strain. The results are discussed in terms of band-structure effects. An analytical model is presented to understand the fact that the thermopower decreases if degenerate bands are energetically lifted due to a strain- induced redistribution of states.