Strain engineering of the electronic and thermoelectric properties of titanium trisulphide monolayers

Abstract

The goal of this work is to evaluate the effect of mechanical strain on a number of electronic and thermoelectric properties of TiS3 monolayers. We have used density-functional theory (DFT) calculations at the hybrid HSE06 level to evaluate the response of the electronic band gap and mobilities, as well as the thermopower, the electrical conductivity, the electronic contribution to the thermal conductivity and the power factor. Our calculations indicate that the band gaps can be increased by 44.25%, reaching a value of 1.55 eV from that of the undeformed case of 1.07 eV. The behaviour of HSE06 band gaps agrees well with that calculated at the G0W0 level of theory. We evaluate the variation of electron mobilities with strain and discuss the possible causes of the existent disagreement between experiments and simulations. In addition, our calculations predict small changes in the Seebeck coefficient, whose Sy component can be enhanced by up to 11% with a compression of 5% along the y-axis. On the other hand, the electrical conductivity experiences higher variations, nearly doubling its value from the undeformed case under the semiconductor regime of doping and mechanical deformation. Finally, our predicted power factors can be enhanced by nearly twice under the same conditions by which the electrical conductivity is also improved, indicating that the latter drives the optimisation of the former.