# Optimal band gap for improved thermoelectric performance of two-dimensional Dirac materials

## TL;DR

This study identifies an optimal band gap range for 2D Dirac materials to maximize thermoelectric efficiency, showing gapped materials outperform gapless ones and that reducing lattice thermal conductivity enhances performance.

## Contribution

It demonstrates the existence of an optimal band gap for thermoelectric performance in 2D Dirac materials and highlights the potential for high ZT values with minimal lattice thermal conductivity.

## Key findings

- Gapless 2D Dirac materials have poorer thermoelectric performance.
- An optimal band gap range of 6kBT to 18kBT maximizes ZT.
- Maximum ZT can surpass commercial thermoelectrics with zero lattice thermal conductivity.

## Abstract

Thermoelectric properties of two-dimensional (2D) Dirac materials are calculated within linearized Boltzmann transport theory and relaxation time approximation. We find that the gapless 2D Dirac material exhibits poorer thermoelectric performance than the gapped one. Furthermore, there exists an optimal band gap for maximizing the figure of merit (ZT) in the gapped 2D Dirac material. The optimal band gap ranges from 6kBT to 18kBT, where kB is the Boltzmann constant and T is the operating temperature in kelvin. This result, which is similar to that for bulk semiconductors, indicates the importance of having narrow gaps to achieve the best thermoelectrics in 2D systems. Larger maximum ZTs can also be obtained by suppressing the lattice thermal conductivity. In the most ideal case where the lattice thermal conductivity is zero (leaving the electron thermal conductivity alone), the maximum ZT in the gapped 2D Dirac material is many times ZT of commercial thermoelectric materials.