Structural arrangement and improved thermoelectric figure of merit in hexagonal SiX (X = N, P, As, Sb, Bi) monolayers: understanding from first-principles calculations

Materials with thermoelectric (TE) efficiencies comparable to Carnot efficiency are desirable for applications in devices that use TE effects to produce electricity from heat. The figure of merit of a TE material is a measure of its efficiency. This quantity is determined by the intricate interplay of electronic and thermal transport parameters. Layered materials at low dimensions, such as 2D monolayers, have been in focus with regard to the quest for new TE materials. Group III-VI semiconductors in their 2D monolayers have exhibited fascinating TE properties. Naturally, it is expected that isoelectronic IV-V semiconductors will possess similar novelty. In this work, we have investigated the electronic, dynamical and TE properties of IV-V monolayer SiN, SiP, SiAs, SiSb and SiBi using first-principles electronic structure methods in conjunction with the semiclassical Boltzmann transport theory. Unlike previous studies, here the focus was to compute and analyse the effects of structural arrangements on TE properties. We found that upon consideration of an alternative stacking arrangement in the systems, significant changes occur in the transport phenomena, leading to a large figure of merit and thus TE efficiency. A comprehensive comparative analysis is presented to interpret the results. This work bears significance in the fact that it demonstrates a very important structure-property relationship aspect for these compounds that has been overlooked so far, and this approach may lead to the discovery of new TE materials with desirable efficiencies.