First-Principles Calculations of Heteroanionic Monochalcogenide Alloy Nanosheets with Direction-dependent Properties for Anisotropic Optoelectronics

Exploring beyond monoelemental and binary two-dimensional (2D) nanomaterials is an important step to further engineer and functionalize well-known 2D nanomaterials for the next-generation technologies. In this work, using state-of-the-art first-principles electronic structure calculations and statistical sampling of structural configurations, we examine the influence of anionic exchange in two monolayer group IV (namely, Ge- and Sn-based) monochalcogenides. Using chemical bonding analysis, we demonstrate the link between anisotropic lattice properties and band structure-derived characteristics. We also show how this structural anisotropy and iono-covalency chemical bonding may both strongly influence the direction-dependent optical responses and have a milder effect on direction-dependent thermoelectric power factor in these monolayer group IV alloys. This allows one to consider the linear Vegard’s relation for anionic engineering of monolayer group IV alloys and further explore strong (and weak) anisotropy in their direction-dependent material properties.