The DFT Study of Electronic and Optical Properties of the Surface Functional SiGe, GeSn and GeSn Nanostructures

The electronic and optical properties of Si, Ge, and Sn nanostructures are widely studied for various applications, including drug delivery, cell imaging, biosensing and biomedical. This work considers the effect on electronic and optical properties of SiGe, SiSn and GeSn nanostructures by varying the surface functional and the structure size. The considered structures are about spherical-shaped, with a zinc-blende crystal structure, and H, O+H, OH, and NH2-capped. The optimized structures and their absorption energies are calculated by density functional theory (DFT) and time-dependent density functional theory TD-DFT techniques. In all calculations, the B3LYP and 6-31g basis are used for investigation of electronic and optical properties for SiGe nanostructures, while the LanL2DZ is used for SiSn and GeSn nanostructures. The results show that the optical gap depends not only on the size but also on the terminations on the nanostructure surface. This dependence allows for the possibility of electronic and optical gap engineering.