Fundamentals of 2D Semiconducting Materials

A new field of two-dimensional (2D) physics has been opened by 2D atomic crystals represented by graphene in recent years. Despite a relatively short research history, the exceptional electrical and optical characteristics of 2D semiconductors make them highly attractive for electronic and optoelectronic purposes. The electronic and optical properties of 2D semiconducting materials (SCMs) are significantly influenced by the molecular orbital (MO) delocalization and stacking effects. These effects play a crucial role in determining the performance and efficiency of these materials in various applications, including electronics, optoelectronics, and energy devices. The phenomenon of MO delocalization in 2D SCMs refers to the spread of electronic wavefunctions over multiple atoms within the material. In these materials, the interaction between adjacent layers leads to the formation of new electronic states called interlayer coupling or interlayer hybridization. This delocalization affects the electronic band structure of the material, including the position of the conduction and valence bands, the bandgap, and the effective masses of charge carriers. Moreover, the consideration of stacking effects is of utmost importance for 2D SCMs. The stacking arrangement of layers can influence the electronic properties, such as the bandgap, optical properties, and the anisotropy of charge transport of 2D SCMs. These effects can alter the exciton dynamics, light-matter interactions, and emission characteristics of these materials.