# Modulation of Semiconductor Superlattice Thermopower Through Symmetry and Strain

## TL;DR

This paper introduces a strain engineering method to significantly enhance the thermopower of Si/Ge superlattices by manipulating structural symmetry and strain, surpassing traditional limits.

## Contribution

It demonstrates how symmetry and strain can be used to tune superlattice bands, leading to a fivefold thermopower enhancement in doped Si/Ge SLs.

## Key findings

- New bands form due to structural symmetry.
- Epitaxial strain significantly modulates thermopower.
- Achieved ~5-fold thermopower increase in strained Si/Ge SLs.

## Abstract

In doped semiconductors and metals, the thermopower decreases with increasing carrier concentration, in agreement with the Pisarenko relation. Here, we demonstrate a new strain engineering approach to increase the thermopower of [001] Si/Ge superlattices (SLs) beyond this relation. Using two independent theoretical modeling approaches, we show that new bands form due to the structural symmetry, and, the SL bands are highly tunable with epitaxial substrate strain. The band shifts lead to a modulated thermopower, with a peak $\sim$5-fold enhancement in strained Si/Ge SLs in the high doping regime.