Improvement in Thermoelectric Performance of SnS Due to Electronic Structure Modification Under Biaxial Strain

Abstract

Ab-initio calculations using the full potential linearized augmented plane-wave technique and the semi-classical Boltzmann theory are used to study thermoelectric properties of unstrained SnS and at 1%, 2% and 3% applied biaxial tensile (BT) strain. The studies are carried out at 800 K for p-type and n-type carriers. For an increase in BT strain, lattice constants of SnS change causing changes in the band structure and increase in the band gap which in turn modifies thermoelectric coefficients. In the case of unstrained SnS, the maximum thermopower (S) obtained is 426 μV/K at carrier concentration 5.40 × 1018 cm−3 for p-type carriers and 435 μV/K at carrier concentration 1.68 × 1018 cm−3 for n-type carriers. At 3% applied BT strain, S is increased to 696 μV/K at carrier concentration 4.61 × 1017 cm−3 for p-type carriers and 624 μV/K at carrier concentration 3.21 × 1017 cm−3 for n-type carriers. The power factor (PF) increases ∼ 2 times at 3% BT strain as compared to unstrained SnS, and it is 6.20 mW K−2 m−1 for p-type carriers. For n-type carriers, PF at 3% applied BT is slightly less than the PF for unstrained SnS, which is 6.81 mW K−2 m−1. For both types of carriers, the figure of merit (ZT) is found to be ∼ 1.5 for unstrained SnS. For p-type carriers ZT is enhanced 1.4 times at 3% applied BT strain as compared to that of unstrained SnS. However, for n-type carriers, ZT does not change drastically with increase in BT strain.