Ge–Si and Si–Ge core–shell nanocrystals: Theoretical study

The electronic and optical properties of Ge−Si and Si−Ge core–shell nanocrystals (NCs) were investigated using pure and time-dependent density functional theory calculations. The Si and Ge NCs with diameter of about 2 nm are considered for constructing of the Ge−Si and Si−Ge core–shell NCs, respectively. The dependency of the optical and electronic properties of Ge−Si and Si−Ge core–shell NCs was studied with defined structural parameters as the ratio of the core radius (R₁) to the NC radius (R₂). It is found that the single particle energy gap, optical gap and exciton binding energy of the different core–shell NCs are strongly dependent on the structural parameter of R₁ / R₂. It is shown that the energy gap, optical gap and lowest exciton binding energy of the both core–shell NCs can be modulated with structural parameter variations. The results presented in this work can be used for development and tuning of the electronic and optoelectronic properties of nanodevices based on Si and Ge core–shell NCs. - Highlights: • Optical properties of Ge−Si and Si−Ge core–shell nanocrystals were investigated. • Optical properties of the core–shell NCs were studied with core radius changes. • The exciton binding energy and HOMO–LUMO gap of the core shells were discussed