Van der Waals heterostructure configuration effect on exciton and thermoelectric characteristics

TL;DR

This study investigates how different stacking configurations of 2D van der Waals heterostructures influence their electronic, excitonic, and thermoelectric properties using advanced ab initio calculations, revealing significant effects on band gaps and hot electron behavior.

Contribution

It provides a comprehensive analysis of the impact of heterostructure stacking on electronic and thermoelectric characteristics, highlighting the importance of atomic layering in tuning material properties.

Findings

Layering same or different atoms drastically alters band alignment and exciton binding energy.

Certain configurations enhance thermoelectric performance due to low heat conductivity and increased density of states.

High configuration heterostructures facilitate hot electron relaxation, affecting thermal stability.

Abstract

A GW calculation based on a truncated Coulomb interaction with an added small q limit was applied to 2D van der Waals heterolayered structures, and the Kane dispersion model was used to determine the accurate band gap edge. All ab initio calculations were performed with the gpaw package. Our findings show that layering the same or different types of atoms with a vacuum in between has an enormous impact on band alignment, effective mass of holes and electrons, exciton binding energy, thermoelectric characteristics, density of hot electrons, and electronic band gaps.Thus, layered interactions of the same kind constrain the configuration to have a direct band gap, whereas different kinds allow for an indirect gap, resulting in an indirect exciton with a greater binding energy due to the band confinement effect. Furthermore, the heterostructure of the highest configuration facilitates the relaxation of hot electrons by forming unoccupied states. This leads to a high density of hot electrons dispersing over unoccupied states, which lessens their sensitivity to temperature; in other words, thermal drop prolongs electron-hole pairing. $\mathrm{MoSe_{2}-MoS_{2}}$ and $\mathrm{MoSeSe-MoSSe}$ have an improved Seebeck coefficient among the various possible configurations because of their low heat conductivity, ability to produce a higher density of states and empty states, improved optical gap, and multiple excitation peaks that resemble the experimental photoluminescence spectrum.