First-principles calculations of electronic, optical and thermoelectric properties of the Ge2SeS/GeSe van der Waals heterostructure

In this research, we systematically investigate the electronic structure, optical and thermoelectric properties of the Ge2SeS/GeSe van der Waals (vdW) heterostructure in comparison to the Ge2SeS and GeSe monolayers by using density functional theory (DFT) implemented in Quantum ESPRESSO. We have constructed two configurations of the Ge2SeS/GeSe heterostructure by stacking the Ge2SeS monolayer on top of the GeSe monolayer (Stacking A1 and A2). According to our calculations, the calculated indirect electronic band gaps of both Stacking A1 and Stacking A2 are Eg = 0.80 eV and 0.88 eV, respectively. The transfer of charges from the Ge2SeS to the GeSe monolayer for both configurations has been predicted. By Bader charge analysis, the charge transfers for Stacking A1 and A2 are approximately 0.013 e and 0.020 e, respectively. The coefficient of absorption for the Ge2SeS/GeSe heterostructure is higher than that for Ge2SeS and GeSe monolayers in both regions of the spectrum (visible, and UV). Moreover, the Ge2SeS/GeSe heterostructure has a very good absorbing capability of light in the visible region up to 85 × 104 cm−1. Our calculations yielded a high thermoelectrical electronic figure of merit (ZTe) of 12.64 and 2.27 for Stacking A1 and A2, respectively. As a result, our findings show that the Ge2SeS/GeSe heterostructure is a promising material for thermoelectric and optoelectronic applications.