Electronic structure of and quantum size effect in III-V and II-VI semiconducting nanocrystals using a realistic tight binding approach

We analyze the electronic structure of group III-V semiconductors obtained within full potential linearized augmented plane wave FP-LAPW method and arrive at a realistic and minimal tight-binding model, parametrized to provide an accurate description of both valence and conduction bands. It is shown that the cation sp3anion sp3d5 basis along with the next nearest neighbor model for hopping interactions is sufficient to describe the electronic structure of these systems over a wide energy range, obviating the use of any fictitious s* orbital, employed previously. Similar analyses were also performed for the II-VI semiconductors, using the more accurate FP-LAPW method compared to previous approaches, in order to enhance reliability of the parameter values. Using these parameters, we calculate the electronic structure of III-V and II-VI nanocrystals in real space with sizes ranging up to about 7 nm in diameter, establishing a quantitatively accurate description of the bandgap variation with sizes for the various nanocrystals by comparing with available experimental results from the literature.