Density functional theory studies of electronic and optical properties: Bulk, monolayer, and bilayer GeSe

The control over the thickness of layered structures is a crucial approach for tailoring the electronic, optical, and mechanical properties of two-dimensional transition metal chalcogenide semiconductors, which serve as a promising foundation for the future advanced energy-harvesting technologies. Here, we systematically investigated the layer-dependent properties of germanium selenide (GeSe) by performing theoretical density functional theory (DFT) calculations across bulk, monolayer and bilayer structures. The results reveal significant variations in the bandgap corresponding to changes in the layer number, underscoring the pivotal role of layer engineering in modulating the electronic structures of GeSe. The electronic band structure of GeSe was investigated by employing two different approaches: the generalized gradient approximation (GGA) with Perdew-Burke-Ernzerhof (PBE) and HSE06 functional, while also considering the influence of spin-orbit coupling (SOC). The inclusion of SOC resulted in a notable reduction in the electronic bandgap of bulk GeSe. This study investigates the optical properties, exploring how layer thickness influences parameters, including optical conductivity, absorption coefficient and refractive index. This comprehensive theoretical investigation provides crucial insights into the layer-dependent behavior of monochalcogenides GeSe, laying the groundwork for the development and optimization of GeSe-based future optoelectronic devices.