Optical and Structural Properties of Metal Chalcogenide Semiconductor Nanostructures

Metal chalcogenides have received a considerable attention during last few years owing to their excellent physiochemical properties such as semiconductivity, low-temperature superconductivity, ionic conductivity, intercalation, and optical properties. To expand the applications of these structures in areas such as electronics, catalysis, separation, ion exchange, and gas storage, new novel chalcogenides materials are being developed by modifying their structure and chemical components. By doing so, properties such as band gap, luminescence, pore size, surface area, and thermal stability can be improved considerably. Semiconductor nanostructures have excellent optical and electronic properties, which are very different from the bulk semiconductors. Bulk semiconductors represent the overlapping of infinite number of atomic orbitals and continuous energy levels, which result in the formation of conduction and valence bands. On the other hand, the intrinsic semiconductors have completely separated conduction and valence bands. Whereas in the case of semiconductor nanostructure materials, it has been reported that band gap energy increases with the decrease in the size of the material within some critical range. Especially when the size becomes less than the excitation Bohr radius, continuum energy levels will not be formed due to lesser number of atoms. So, instead of continuum energy levels, electrons and holes are confined in three-dimensional nanocrystallites, resulting in the breakdown of continuum energy bands in to discrete atomic-like energy states. The critical radius of these nanostructures can vary from 2 to 60 nm or so depending on their identity group (IV, III-V, II-VI, or IV-VI). It shows that size plays an important role in the optoelectronic properties of semiconductor nanostructures. Along with the size of semiconductor nanostructures, their structure also influences both the physical and chemical properties. Nanocrystal surfaces often have trap sites caused by structural defects, such as vacancies or lattice mismatches, unsaturated bonds, and other surface discontinuities. So, in this chapter, we discuss and review in detail the optical properties and structural defects of chalcogenides nanostructures and their modern applications in different challenging fields.