Electronic properties of semiconducting Ca2Si silicide: From bulk to nanostructures by means of first principles calculations

Abstract

Results of our ab initio calculations have revealed changes in electronic properties in Ca2Si semiconducting silicide when reducing dimensionality from bulk to slabs and, eventually, to nanowires. In the case of the bulk, Ca2Si is found to be a direct band-gap semiconductor with the band-gap value of 0.30, 0.60, and 0.79 eV by using the generalized gradient approximation, the modified Becke–Johnson exchange potential and the screened hybrid functional, respectively. We have also identified that among Ca2Si(001), (010), and (100) surfaces the (100) one has the lowest surface energy. Ca2Si slabs with (010) or (100) surfaces are predicted to be semiconductors, while (001) surface provides metallic properties due to surface states. The role of the surface states in the band-gap variation is also discussed. In the case of Ca2Si nanowires with <001>, <010>, and <100> axes and different morphologies only the 〈001〉 orientation guarantees semiconducting properties because of absence of {001} facets which induce metallic properties as for the corresponding slab.